"""
Google Gmail MCP Tools

This module provides MCP tools for interacting with the Gmail API.
"""

import logging
import asyncio
import base64
import re
import ssl
import mimetypes
from html.parser import HTMLParser
from typing import Annotated, Optional, List, Dict, Literal, Any

from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from email.mime.base import MIMEBase
from email import encoders
from email.utils import formataddr

from pydantic import Field
from googleapiclient.errors import HttpError

from auth.service_decorator import require_google_service
from core.utils import handle_http_errors, validate_file_path, UserInputError
from core.server import server
from auth.scopes import (
    GMAIL_SEND_SCOPE,
    GMAIL_COMPOSE_SCOPE,
    GMAIL_MODIFY_SCOPE,
    GMAIL_LABELS_SCOPE,
)

logger = logging.getLogger(__name__)

GMAIL_BATCH_SIZE = 25
GMAIL_REQUEST_DELAY = 0.1
HTML_BODY_TRUNCATE_LIMIT = 20000

GMAIL_METADATA_HEADERS = [
    "Subject",
    "From",
    "To",
    "Cc",
    "Message-ID",
    "In-Reply-To",
    "References",
    "Date",
]
LOW_VALUE_TEXT_PLACEHOLDERS = (
    "your client does not support html",
    "view this email in your browser",
    "open this email in your browser",
)
LOW_VALUE_TEXT_FOOTER_MARKERS = (
    "mailing list",
    "mailman/listinfo",
    "unsubscribe",
    "list-unsubscribe",
    "manage preferences",
)
LOW_VALUE_TEXT_HTML_DIFF_MIN = 80


class _HTMLTextExtractor(HTMLParser):
    """Extract readable text from HTML using stdlib."""

    def __init__(self):
        super().__init__()
        self._text = []
        self._skip = False

    def handle_starttag(self, tag, attrs):
        self._skip = tag in ("script", "style")

    def handle_endtag(self, tag):
        if tag in ("script", "style"):
            self._skip = False

    def handle_data(self, data):
        if not self._skip:
            self._text.append(data)

    def get_text(self) -> str:
        return " ".join("".join(self._text).split())


def _html_to_text(html: str) -> str:
    """Convert HTML to readable plain text."""
    try:
        parser = _HTMLTextExtractor()
        parser.feed(html)
        return parser.get_text()
    except Exception:
        return html


def _extract_message_body(payload):
    """
    Helper function to extract plain text body from a Gmail message payload.
    (Maintained for backward compatibility)

    Args:
        payload (dict): The message payload from Gmail API

    Returns:
        str: The plain text body content, or empty string if not found
    """
    bodies = _extract_message_bodies(payload)
    return bodies.get("text", "")


def _extract_message_bodies(payload):
    """
    Helper function to extract both plain text and HTML bodies from a Gmail message payload.

    Args:
        payload (dict): The message payload from Gmail API

    Returns:
        dict: Dictionary with 'text' and 'html' keys containing body content
    """
    text_body = ""
    html_body = ""
    parts = [payload] if "parts" not in payload else payload.get("parts", [])

    part_queue = list(parts)  # Use a queue for BFS traversal of parts
    while part_queue:
        part = part_queue.pop(0)
        mime_type = part.get("mimeType", "")
        body_data = part.get("body", {}).get("data")

        if body_data:
            try:
                decoded_data = base64.urlsafe_b64decode(body_data).decode(
                    "utf-8", errors="ignore"
                )
                if mime_type == "text/plain" and not text_body:
                    text_body = decoded_data
                elif mime_type == "text/html" and not html_body:
                    html_body = decoded_data
            except Exception as e:
                logger.warning(f"Failed to decode body part: {e}")

        # Add sub-parts to queue for multipart messages
        if mime_type.startswith("multipart/") and "parts" in part:
            part_queue.extend(part.get("parts", []))

    # Check the main payload if it has body data directly
    if payload.get("body", {}).get("data"):
        try:
            decoded_data = base64.urlsafe_b64decode(payload["body"]["data"]).decode(
                "utf-8", errors="ignore"
            )
            mime_type = payload.get("mimeType", "")
            if mime_type == "text/plain" and not text_body:
                text_body = decoded_data
            elif mime_type == "text/html" and not html_body:
                html_body = decoded_data
        except Exception as e:
            logger.warning(f"Failed to decode main payload body: {e}")

    return {"text": text_body, "html": html_body}


def _format_body_content(text_body: str, html_body: str) -> str:
    """
    Helper function to format message body content with HTML fallback and truncation.
    Detects useless text/plain fallbacks (e.g., "Your client does not support HTML").

    Args:
        text_body: Plain text body content
        html_body: HTML body content

    Returns:
        Formatted body content string
    """
    text_stripped = text_body.strip()
    html_stripped = html_body.strip()
    html_text = _html_to_text(html_stripped).strip() if html_stripped else ""

    plain_lower = " ".join(text_stripped.split()).lower()
    html_lower = " ".join(html_text.split()).lower()
    plain_is_low_value = plain_lower and (
        any(marker in plain_lower for marker in LOW_VALUE_TEXT_PLACEHOLDERS)
        or (
            any(marker in plain_lower for marker in LOW_VALUE_TEXT_FOOTER_MARKERS)
            and len(html_lower) >= len(plain_lower) + LOW_VALUE_TEXT_HTML_DIFF_MIN
        )
        or (
            len(html_lower) >= len(plain_lower) + LOW_VALUE_TEXT_HTML_DIFF_MIN
            and html_lower.endswith(plain_lower)
        )
    )

    # Prefer plain text, but fall back to HTML when plain text is empty or clearly low-value.
    use_html = html_text and (
        not text_stripped or "<!--" in text_stripped or plain_is_low_value
    )

    if use_html:
        content = html_text
        if len(content) > HTML_BODY_TRUNCATE_LIMIT:
            content = content[:HTML_BODY_TRUNCATE_LIMIT] + "\n\n[Content truncated...]"
        return content
    elif text_stripped:
        return text_body
    else:
        return "[No readable content found]"


def _append_signature_to_body(
    body: str, body_format: Literal["plain", "html"], signature_html: str
) -> str:
    """Append a Gmail signature to the outgoing body, preserving body format."""
    if not signature_html or not signature_html.strip():
        return body

    if body_format == "html":
        separator = "<br><br>" if body.strip() else ""
        return f"{body}{separator}{signature_html}"

    signature_text = _html_to_text(signature_html).strip()
    if not signature_text:
        return body
    separator = "\n\n" if body.strip() else ""
    return f"{body}{separator}{signature_text}"


async def _fetch_original_for_quote(
    service, thread_id: str, in_reply_to: Optional[str] = None
) -> Optional[dict]:
    """Fetch the original message from a thread for quoting in a reply.

    When *in_reply_to* is provided the function looks for that specific
    Message-ID inside the thread.  Otherwise it falls back to the last
    message in the thread.

    Returns a dict with keys: sender, date, text_body, html_body -- or
    *None* when the message cannot be retrieved.
    """
    try:
        thread_data = await asyncio.to_thread(
            service.users()
            .threads()
            .get(userId="me", id=thread_id, format="full")
            .execute
        )
    except Exception as e:
        logger.warning(f"Failed to fetch thread {thread_id} for quoting: {e}")
        return None

    messages = thread_data.get("messages", [])
    if not messages:
        return None

    target = None
    if in_reply_to:
        for msg in messages:
            headers = {
                h["name"]: h["value"] for h in msg.get("payload", {}).get("headers", [])
            }
            if headers.get("Message-ID") == in_reply_to:
                target = msg
                break
    if target is None:
        target = messages[-1]

    headers = {
        h["name"]: h["value"] for h in target.get("payload", {}).get("headers", [])
    }
    bodies = _extract_message_bodies(target.get("payload", {}))
    return {
        "sender": headers.get("From", "unknown"),
        "date": headers.get("Date", ""),
        "text_body": bodies.get("text", ""),
        "html_body": bodies.get("html", ""),
    }


def _build_quoted_reply_body(
    reply_body: str,
    body_format: Literal["plain", "html"],
    signature_html: str,
    original: dict,
) -> str:
    """Assemble reply body + signature + quoted original message.

    Layout:
        reply_body
        -- signature --
        On {date}, {sender} wrote:
        > quoted original
    """
    import html as _html_mod

    if original.get("date"):
        attribution = f"On {original['date']}, {original['sender']} wrote:"
    else:
        attribution = f"{original['sender']} wrote:"

    if body_format == "html":
        # Signature
        sig_block = ""
        if signature_html and signature_html.strip():
            sig_block = f"<br><br>{signature_html}"

        # Quoted original
        orig_html = original.get("html_body") or ""
        if not orig_html:
            orig_text = original.get("text_body", "")
            orig_html = f"<pre>{_html_mod.escape(orig_text)}</pre>"

        quote_block = (
            '<br><br><div class="gmail_quote">'
            f"<span>{_html_mod.escape(attribution)}</span><br>"
            '<blockquote style="margin:0 0 0 .8ex;border-left:1px solid #ccc;padding-left:1ex">'
            f"{orig_html}"
            "</blockquote></div>"
        )
        return f"{reply_body}{sig_block}{quote_block}"

    # Plain text path
    sig_block = ""
    if signature_html and signature_html.strip():
        sig_text = _html_to_text(signature_html).strip()
        if sig_text:
            sig_block = f"\n\n{sig_text}"

    orig_text = original.get("text_body") or ""
    if not orig_text and original.get("html_body"):
        orig_text = _html_to_text(original["html_body"])
    quoted_lines = "\n".join(f"> {line}" for line in orig_text.splitlines())

    return f"{reply_body}{sig_block}\n\n{attribution}\n{quoted_lines}"


async def _get_send_as_signature_html(service, from_email: Optional[str] = None) -> str:
    """
    Fetch signature HTML from Gmail send-as settings.

    Returns empty string when the account has no signature configured or the
    OAuth token cannot access settings endpoints.
    """
    try:
        response = await asyncio.to_thread(
            service.users().settings().sendAs().list(userId="me").execute
        )
    except HttpError as e:
        status = getattr(getattr(e, "resp", None), "status", None)
        if status in {401, 403}:
            logger.info(
                "Skipping Gmail signature fetch: missing auth/scope for settings endpoint."
            )
            return ""
        logger.warning(f"Failed to fetch Gmail send-as signatures: {e}")
        return ""
    except Exception as e:
        logger.warning(f"Failed to fetch Gmail send-as signatures: {e}")
        return ""

    send_as_entries = response.get("sendAs", [])
    if not send_as_entries:
        return ""

    if from_email:
        from_email_normalized = from_email.strip().lower()
        for entry in send_as_entries:
            if entry.get("sendAsEmail", "").strip().lower() == from_email_normalized:
                return entry.get("signature", "") or ""

    for entry in send_as_entries:
        if entry.get("isPrimary"):
            return entry.get("signature", "") or ""

    return send_as_entries[0].get("signature", "") or ""


def _format_attachment_result(attached_count: int, requested_count: int) -> str:
    """Format attachment result message for user-facing responses."""
    if requested_count <= 0:
        return ""
    if attached_count == requested_count:
        return f" with {attached_count} attachment(s)"
    return f" with {attached_count}/{requested_count} attachment(s) attached"


def _extract_attachments(payload: dict) -> List[Dict[str, Any]]:
    """
    Extract attachment metadata from a Gmail message payload.

    Args:
        payload: The message payload from Gmail API

    Returns:
        List of attachment dictionaries with filename, mimeType, size, and attachmentId
    """
    attachments = []

    def search_parts(part):
        """Recursively search for attachments in message parts"""
        # Check if this part is an attachment
        if part.get("filename") and part.get("body", {}).get("attachmentId"):
            attachments.append(
                {
                    "filename": part["filename"],
                    "mimeType": part.get("mimeType", "application/octet-stream"),
                    "size": part.get("body", {}).get("size", 0),
                    "attachmentId": part["body"]["attachmentId"],
                }
            )

        # Recursively search sub-parts
        if "parts" in part:
            for subpart in part["parts"]:
                search_parts(subpart)

    # Start searching from the root payload
    search_parts(payload)
    return attachments


def _extract_headers(payload: dict, header_names: List[str]) -> Dict[str, str]:
    """
    Extract specified headers from a Gmail message payload.

    Args:
        payload: The message payload from Gmail API
        header_names: List of header names to extract

    Returns:
        Dict mapping header names to their values
    """
    headers = {}
    target_headers = {name.lower(): name for name in header_names}
    for header in payload.get("headers", []):
        header_name_lower = header["name"].lower()
        if header_name_lower in target_headers:
            # Store using the original requested casing
            headers[target_headers[header_name_lower]] = header["value"]
    return headers


def _parse_message_id_chain(header_value: Optional[str]) -> List[str]:
    """Extract Message-IDs from a reply header value."""
    if not header_value:
        return []

    message_ids = re.findall(r"<[^>]+>", header_value)
    if message_ids:
        return message_ids

    return header_value.split()


def _derive_reply_headers(
    thread_message_ids: List[str],
    in_reply_to: Optional[str],
    references: Optional[str],
) -> tuple[Optional[str], Optional[str]]:
    """Fill missing reply headers while preserving caller intent."""
    derived_in_reply_to = in_reply_to
    derived_references = references

    if not thread_message_ids:
        return derived_in_reply_to, derived_references

    if not derived_in_reply_to:
        reference_chain = _parse_message_id_chain(derived_references)
        derived_in_reply_to = (
            reference_chain[-1] if reference_chain else thread_message_ids[-1]
        )

    if not derived_references:
        if derived_in_reply_to and derived_in_reply_to in thread_message_ids:
            reply_index = thread_message_ids.index(derived_in_reply_to)
            derived_references = " ".join(thread_message_ids[: reply_index + 1])
        elif derived_in_reply_to:
            derived_references = derived_in_reply_to
        else:
            derived_references = " ".join(thread_message_ids)

    return derived_in_reply_to, derived_references


async def _fetch_thread_message_ids(service, thread_id: str) -> List[str]:
    """
    Fetch Message-ID headers from a Gmail thread for reply threading.

    Args:
        service: Gmail API service instance
        thread_id: Gmail thread ID

    Returns:
        Message-IDs in thread order. Returns an empty list on failure.
    """
    try:
        thread = await asyncio.to_thread(
            service.users()
            .threads()
            .get(
                userId="me",
                id=thread_id,
                format="metadata",
                metadataHeaders=["Message-ID"],
            )
            .execute
        )
        messages = thread.get("messages", [])
        if not messages:
            return []

        # Collect all Message-IDs in thread order
        message_ids = []
        for msg in messages:
            headers = _extract_headers(msg.get("payload", {}), ["Message-ID"])
            mid = headers.get("Message-ID")
            if mid:
                message_ids.append(mid)

        return message_ids
    except Exception as e:
        logger.warning(
            f"Failed to fetch thread Message-IDs for thread {thread_id}: {e}"
        )
        return []


def _prepare_gmail_message(
    subject: str,
    body: str,
    to: Optional[str] = None,
    cc: Optional[str] = None,
    bcc: Optional[str] = None,
    thread_id: Optional[str] = None,
    in_reply_to: Optional[str] = None,
    references: Optional[str] = None,
    body_format: Literal["plain", "html"] = "plain",
    from_email: Optional[str] = None,
    from_name: Optional[str] = None,
    attachments: Optional[List[Dict[str, str]]] = None,
) -> tuple[str, Optional[str], int]:
    """
    Prepare a Gmail message with threading and attachment support.

    Args:
        subject: Email subject
        body: Email body content
        to: Optional recipient email address
        cc: Optional CC email address
        bcc: Optional BCC email address
        thread_id: Optional Gmail thread ID to reply within
        in_reply_to: Optional Message-ID of the message being replied to
        references: Optional chain of Message-IDs for proper threading
        body_format: Content type for the email body ('plain' or 'html')
        from_email: Optional sender email address
        from_name: Optional sender display name (e.g., "Peter Hartree")
        attachments: Optional list of attachments. Each can have 'path' (file path) OR 'content' (base64) + 'filename'

    Returns:
        Tuple of (raw_message, thread_id, attached_count) where raw_message is base64 encoded
    """
    # Handle reply subject formatting
    reply_subject = subject
    if in_reply_to and not subject.lower().startswith("re:"):
        reply_subject = f"Re: {subject}"

    # Prepare the email
    normalized_format = body_format.lower()
    if normalized_format not in {"plain", "html"}:
        raise ValueError("body_format must be either 'plain' or 'html'.")

    # Use multipart if attachments are provided
    attached_count = 0
    if attachments:
        message = MIMEMultipart()
        message.attach(MIMEText(body, normalized_format))

        # Process attachments
        for attachment in attachments:
            file_path = attachment.get("path")
            filename = attachment.get("filename")
            content_base64 = attachment.get("content")
            mime_type = attachment.get("mime_type")

            try:
                # If path is provided, read and encode the file
                if file_path:
                    path_obj = validate_file_path(file_path)
                    if not path_obj.exists():
                        logger.error(f"File not found: {file_path}")
                        continue

                    # Read file content
                    with open(path_obj, "rb") as f:
                        file_data = f.read()

                    # Use provided filename or extract from path
                    if not filename:
                        filename = path_obj.name

                    # Auto-detect MIME type if not provided
                    if not mime_type:
                        mime_type, _ = mimetypes.guess_type(str(path_obj))
                        if not mime_type:
                            mime_type = "application/octet-stream"

                # If content is provided (base64), decode it
                elif content_base64:
                    if not filename:
                        logger.warning("Skipping attachment: missing filename")
                        continue

                    file_data = base64.b64decode(content_base64)

                    if not mime_type:
                        mime_type = "application/octet-stream"

                else:
                    logger.warning("Skipping attachment: missing both path and content")
                    continue

                # Create MIME attachment
                main_type, sub_type = mime_type.split("/", 1)
                part = MIMEBase(main_type, sub_type)
                part.set_payload(file_data)
                encoders.encode_base64(part)

                # Use add_header with keyword argument so Python's email
                # library applies RFC 2231 encoding for non-ASCII filenames
                # (e.g. filename*=utf-8''Pr%C3%BCfbericht.pdf).  Manual
                # string formatting would drop non-ASCII characters and cause
                # Gmail to display "noname".
                safe_filename = (
                    (filename or "attachment")
                    .replace("\r", "")
                    .replace("\n", "")
                    .replace("\x00", "")
                ) or "attachment"

                part.add_header(
                    "Content-Disposition", "attachment", filename=safe_filename
                )

                message.attach(part)
                attached_count += 1
                logger.info(f"Attached file: {filename} ({len(file_data)} bytes)")
            except Exception as e:
                logger.error(f"Failed to attach {filename or file_path}: {e}")
                continue
    else:
        message = MIMEText(body, normalized_format)

    message["Subject"] = reply_subject

    # Add sender if provided
    if from_email:
        if from_name:
            # Sanitize from_name to prevent header injection
            safe_name = (
                from_name.replace("\r", "").replace("\n", "").replace("\x00", "")
            )
            message["From"] = formataddr((safe_name, from_email))
        else:
            message["From"] = from_email

    # Add recipients if provided
    if to:
        message["To"] = to
    if cc:
        message["Cc"] = cc
    if bcc:
        message["Bcc"] = bcc

    # Add reply headers for threading
    if in_reply_to:
        message["In-Reply-To"] = in_reply_to

    if references:
        message["References"] = references

    # Encode message
    raw_message = base64.urlsafe_b64encode(message.as_bytes()).decode()

    return raw_message, thread_id, attached_count


def _generate_gmail_web_url(item_id: str, account_index: int = 0) -> str:
    """
    Generate Gmail web interface URL for a message or thread ID.
    Uses #all to access messages from any Gmail folder/label (not just inbox).

    Args:
        item_id: Gmail message ID or thread ID
        account_index: Google account index (default 0 for primary account)

    Returns:
        Gmail web interface URL that opens the message/thread in Gmail web interface
    """
    return f"https://mail.google.com/mail/u/{account_index}/#all/{item_id}"


def _format_gmail_results_plain(
    messages: list, query: str, next_page_token: Optional[str] = None
) -> str:
    """Format Gmail search results in clean, LLM-friendly plain text."""
    if not messages:
        return f"No messages found for query: '{query}'"

    lines = [
        f"Found {len(messages)} messages matching '{query}':",
        "",
        "📧 MESSAGES:",
    ]

    for i, msg in enumerate(messages, 1):
        # Handle potential null/undefined message objects
        if not msg or not isinstance(msg, dict):
            lines.extend(
                [
                    f"  {i}. Message: Invalid message data",
                    "     Error: Message object is null or malformed",
                    "",
                ]
            )
            continue

        # Handle potential null/undefined values from Gmail API
        message_id = msg.get("id")
        thread_id = msg.get("threadId")

        # Convert None, empty string, or missing values to "unknown"
        if not message_id:
            message_id = "unknown"
        if not thread_id:
            thread_id = "unknown"

        if message_id != "unknown":
            message_url = _generate_gmail_web_url(message_id)
        else:
            message_url = "N/A"

        if thread_id != "unknown":
            thread_url = _generate_gmail_web_url(thread_id)
        else:
            thread_url = "N/A"

        lines.extend(
            [
                f"  {i}. Message ID: {message_id}",
                f"     Web Link: {message_url}",
                f"     Thread ID: {thread_id}",
                f"     Thread Link: {thread_url}",
                "",
            ]
        )

    lines.extend(
        [
            "💡 USAGE:",
            "  • Pass the Message IDs **as a list** to get_gmail_messages_content_batch()",
            "    e.g. get_gmail_messages_content_batch(message_ids=[...])",
            "  • Pass the Thread IDs to get_gmail_thread_content() (single) or get_gmail_threads_content_batch() (batch)",
        ]
    )

    # Add pagination info if there's a next page
    if next_page_token:
        lines.append("")
        lines.append(
            f"📄 PAGINATION: To get the next page, call search_gmail_messages again with page_token='{next_page_token}'"
        )

    return "\n".join(lines)


@server.tool()
@handle_http_errors("search_gmail_messages", is_read_only=True, service_type="gmail")
@require_google_service("gmail", "gmail_read")
async def search_gmail_messages(
    service,
    query: str,
    user_google_email: str,
    page_size: int = 10,
    page_token: Optional[str] = None,
) -> str:
    """
    Searches messages in a user's Gmail account based on a query.
    Returns both Message IDs and Thread IDs for each found message, along with Gmail web interface links for manual verification.
    Supports pagination via page_token parameter.

    Args:
        query (str): The search query. Supports standard Gmail search operators.
        user_google_email (str): The user's Google email address. Required.
        page_size (int): The maximum number of messages to return. Defaults to 10.
        page_token (Optional[str]): Token for retrieving the next page of results. Use the next_page_token from a previous response.

    Returns:
        str: LLM-friendly structured results with Message IDs, Thread IDs, and clickable Gmail web interface URLs for each found message.
        Includes pagination token if more results are available.
    """
    logger.info(
        f"[search_gmail_messages] Email: '{user_google_email}', Query: '{query}', Page size: {page_size}"
    )

    # Build the API request parameters
    request_params = {"userId": "me", "q": query, "maxResults": page_size}

    # Add page token if provided
    if page_token:
        request_params["pageToken"] = page_token
        logger.info("[search_gmail_messages] Using page_token for pagination")

    response = await asyncio.to_thread(
        service.users().messages().list(**request_params).execute
    )

    # Handle potential null response (but empty dict {} is valid)
    if response is None:
        logger.warning("[search_gmail_messages] Null response from Gmail API")
        return f"No response received from Gmail API for query: '{query}'"

    messages = response.get("messages", [])
    # Additional safety check for null messages array
    if messages is None:
        messages = []

    # Extract next page token for pagination
    next_page_token = response.get("nextPageToken")

    formatted_output = _format_gmail_results_plain(messages, query, next_page_token)

    logger.info(f"[search_gmail_messages] Found {len(messages)} messages")
    if next_page_token:
        logger.info(
            "[search_gmail_messages] More results available (next_page_token present)"
        )
    return formatted_output


@server.tool()
@handle_http_errors(
    "get_gmail_message_content", is_read_only=True, service_type="gmail"
)
@require_google_service("gmail", "gmail_read")
async def get_gmail_message_content(
    service, message_id: str, user_google_email: str
) -> str:
    """
    Retrieves the full content (subject, sender, recipients, plain text body) of a specific Gmail message.

    Args:
        message_id (str): The unique ID of the Gmail message to retrieve.
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: The message details including subject, sender, date, Message-ID, recipients (To, Cc), and body content.
    """
    logger.info(
        f"[get_gmail_message_content] Invoked. Message ID: '{message_id}', Email: '{user_google_email}'"
    )

    logger.info(f"[get_gmail_message_content] Using service for: {user_google_email}")

    # Fetch message metadata first to get headers
    message_metadata = await asyncio.to_thread(
        service.users()
        .messages()
        .get(
            userId="me",
            id=message_id,
            format="metadata",
            metadataHeaders=GMAIL_METADATA_HEADERS,
        )
        .execute
    )

    headers = _extract_headers(
        message_metadata.get("payload", {}), GMAIL_METADATA_HEADERS
    )
    subject = headers.get("Subject", "(no subject)")
    sender = headers.get("From", "(unknown sender)")
    to = headers.get("To", "")
    cc = headers.get("Cc", "")
    rfc822_msg_id = headers.get("Message-ID", "")

    # Now fetch the full message to get the body parts
    message_full = await asyncio.to_thread(
        service.users()
        .messages()
        .get(
            userId="me",
            id=message_id,
            format="full",  # Request full payload for body
        )
        .execute
    )

    # Extract both text and HTML bodies using enhanced helper function
    payload = message_full.get("payload", {})
    bodies = _extract_message_bodies(payload)
    text_body = bodies.get("text", "")
    html_body = bodies.get("html", "")

    # Format body content with HTML fallback
    body_data = _format_body_content(text_body, html_body)

    # Extract attachment metadata
    attachments = _extract_attachments(payload)

    content_lines = [
        f"Subject: {subject}",
        f"From:    {sender}",
        f"Date:    {headers.get('Date', '(unknown date)')}",
    ]

    if rfc822_msg_id:
        content_lines.append(f"Message-ID: {rfc822_msg_id}")

    in_reply_to = headers.get("In-Reply-To", "")
    references = headers.get("References", "")
    if in_reply_to:
        content_lines.append(f"In-Reply-To: {in_reply_to}")
    if references:
        content_lines.append(f"References: {references}")

    if to:
        content_lines.append(f"To:      {to}")
    if cc:
        content_lines.append(f"Cc:      {cc}")

    content_lines.append(f"\n--- BODY ---\n{body_data or '[No text/plain body found]'}")

    # Add attachment information if present
    if attachments:
        content_lines.append("\n--- ATTACHMENTS ---")
        for i, att in enumerate(attachments, 1):
            size_kb = att["size"] / 1024
            content_lines.append(
                f"{i}. {att['filename']} ({att['mimeType']}, {size_kb:.1f} KB)\n"
                f"   Attachment ID: {att['attachmentId']}\n"
                f"   Use get_gmail_attachment_content(message_id='{message_id}', attachment_id='{att['attachmentId']}') to download"
            )

    return "\n".join(content_lines)


@server.tool()
@handle_http_errors(
    "get_gmail_messages_content_batch", is_read_only=True, service_type="gmail"
)
@require_google_service("gmail", "gmail_read")
async def get_gmail_messages_content_batch(
    service,
    message_ids: List[str],
    user_google_email: str,
    format: Literal["full", "metadata"] = "full",
) -> str:
    """
    Retrieves the content of multiple Gmail messages in a single batch request.
    Supports up to 25 messages per batch to prevent SSL connection exhaustion.

    Args:
        message_ids (List[str]): List of Gmail message IDs to retrieve (max 25 per batch).
        user_google_email (str): The user's Google email address. Required.
        format (Literal["full", "metadata"]): Message format. "full" includes body, "metadata" only headers.

    Returns:
        str: A formatted list of message contents including subject, sender, date, Message-ID, recipients (To, Cc), and body (if full format).
    """
    logger.info(
        f"[get_gmail_messages_content_batch] Invoked. Message count: {len(message_ids)}, Email: '{user_google_email}'"
    )

    if not message_ids:
        raise Exception("No message IDs provided")

    output_messages = []

    # Process in smaller chunks to prevent SSL connection exhaustion
    for chunk_start in range(0, len(message_ids), GMAIL_BATCH_SIZE):
        chunk_ids = message_ids[chunk_start : chunk_start + GMAIL_BATCH_SIZE]
        results: Dict[str, Dict] = {}

        def _batch_callback(request_id, response, exception):
            """Callback for batch requests"""
            results[request_id] = {"data": response, "error": exception}

        # Try to use batch API
        try:
            batch = service.new_batch_http_request(callback=_batch_callback)

            for mid in chunk_ids:
                if format == "metadata":
                    req = (
                        service.users()
                        .messages()
                        .get(
                            userId="me",
                            id=mid,
                            format="metadata",
                            metadataHeaders=GMAIL_METADATA_HEADERS,
                        )
                    )
                else:
                    req = (
                        service.users()
                        .messages()
                        .get(userId="me", id=mid, format="full")
                    )
                batch.add(req, request_id=mid)

            # Execute batch request
            await asyncio.to_thread(batch.execute)

        except Exception as batch_error:
            # Fallback to sequential processing instead of parallel to prevent SSL exhaustion
            logger.warning(
                f"[get_gmail_messages_content_batch] Batch API failed, falling back to sequential processing: {batch_error}"
            )

            async def fetch_message_with_retry(mid: str, max_retries: int = 3):
                """Fetch a single message with exponential backoff retry for SSL errors"""
                for attempt in range(max_retries):
                    try:
                        if format == "metadata":
                            msg = await asyncio.to_thread(
                                service.users()
                                .messages()
                                .get(
                                    userId="me",
                                    id=mid,
                                    format="metadata",
                                    metadataHeaders=GMAIL_METADATA_HEADERS,
                                )
                                .execute
                            )
                        else:
                            msg = await asyncio.to_thread(
                                service.users()
                                .messages()
                                .get(userId="me", id=mid, format="full")
                                .execute
                            )
                        return mid, msg, None
                    except ssl.SSLError as ssl_error:
                        if attempt < max_retries - 1:
                            # Exponential backoff: 1s, 2s, 4s
                            delay = 2**attempt
                            logger.warning(
                                f"[get_gmail_messages_content_batch] SSL error for message {mid} on attempt {attempt + 1}: {ssl_error}. Retrying in {delay}s..."
                            )
                            await asyncio.sleep(delay)
                        else:
                            logger.error(
                                f"[get_gmail_messages_content_batch] SSL error for message {mid} on final attempt: {ssl_error}"
                            )
                            return mid, None, ssl_error
                    except Exception as e:
                        return mid, None, e

            # Process messages sequentially with small delays to prevent connection exhaustion
            for mid in chunk_ids:
                mid_result, msg_data, error = await fetch_message_with_retry(mid)
                results[mid_result] = {"data": msg_data, "error": error}
                # Brief delay between requests to allow connection cleanup
                await asyncio.sleep(GMAIL_REQUEST_DELAY)

        # Process results for this chunk
        for mid in chunk_ids:
            entry = results.get(mid, {"data": None, "error": "No result"})

            if entry["error"]:
                output_messages.append(f"⚠️ Message {mid}: {entry['error']}\n")
            else:
                message = entry["data"]
                if not message:
                    output_messages.append(f"⚠️ Message {mid}: No data returned\n")
                    continue

                # Extract content based on format
                payload = message.get("payload", {})

                if format == "metadata":
                    headers = _extract_headers(payload, GMAIL_METADATA_HEADERS)
                    subject = headers.get("Subject", "(no subject)")
                    sender = headers.get("From", "(unknown sender)")
                    to = headers.get("To", "")
                    cc = headers.get("Cc", "")
                    rfc822_msg_id = headers.get("Message-ID", "")

                    in_reply_to = headers.get("In-Reply-To", "")
                    references = headers.get("References", "")

                    msg_output = (
                        f"Message ID: {mid}\nSubject: {subject}\nFrom: {sender}\n"
                        f"Date: {headers.get('Date', '(unknown date)')}\n"
                    )
                    if rfc822_msg_id:
                        msg_output += f"Message-ID: {rfc822_msg_id}\n"
                    if in_reply_to:
                        msg_output += f"In-Reply-To: {in_reply_to}\n"
                    if references:
                        msg_output += f"References: {references}\n"

                    if to:
                        msg_output += f"To: {to}\n"
                    if cc:
                        msg_output += f"Cc: {cc}\n"
                    msg_output += f"Web Link: {_generate_gmail_web_url(mid)}\n"

                    output_messages.append(msg_output)
                else:
                    # Full format - extract body too
                    headers = _extract_headers(payload, GMAIL_METADATA_HEADERS)
                    subject = headers.get("Subject", "(no subject)")
                    sender = headers.get("From", "(unknown sender)")
                    to = headers.get("To", "")
                    cc = headers.get("Cc", "")
                    rfc822_msg_id = headers.get("Message-ID", "")

                    # Extract both text and HTML bodies using enhanced helper function
                    bodies = _extract_message_bodies(payload)
                    text_body = bodies.get("text", "")
                    html_body = bodies.get("html", "")

                    # Format body content with HTML fallback
                    body_data = _format_body_content(text_body, html_body)

                    in_reply_to = headers.get("In-Reply-To", "")
                    references = headers.get("References", "")

                    msg_output = (
                        f"Message ID: {mid}\nSubject: {subject}\nFrom: {sender}\n"
                        f"Date: {headers.get('Date', '(unknown date)')}\n"
                    )
                    if rfc822_msg_id:
                        msg_output += f"Message-ID: {rfc822_msg_id}\n"
                    if in_reply_to:
                        msg_output += f"In-Reply-To: {in_reply_to}\n"
                    if references:
                        msg_output += f"References: {references}\n"

                    if to:
                        msg_output += f"To: {to}\n"
                    if cc:
                        msg_output += f"Cc: {cc}\n"
                    msg_output += (
                        f"Web Link: {_generate_gmail_web_url(mid)}\n\n{body_data}\n"
                    )

                    output_messages.append(msg_output)

    # Combine all messages with separators
    final_output = f"Retrieved {len(message_ids)} messages:\n\n"
    final_output += "\n---\n\n".join(output_messages)

    return final_output


@server.tool()
@handle_http_errors(
    "get_gmail_attachment_content", is_read_only=True, service_type="gmail"
)
@require_google_service("gmail", "gmail_read")
async def get_gmail_attachment_content(
    service,
    message_id: str,
    attachment_id: str,
    user_google_email: str,
) -> str:
    """
    Downloads an email attachment and saves it to local disk.

    In stdio mode, returns the local file path for direct access.
    In HTTP mode, returns a temporary download URL (valid for 1 hour).
    May re-fetch message metadata to resolve filename and MIME type.

    Args:
        message_id (str): The ID of the Gmail message containing the attachment.
        attachment_id (str): The ID of the attachment to download.
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: Attachment metadata with either a local file path or download URL.
    """
    logger.info(
        f"[get_gmail_attachment_content] Invoked. Message ID: '{message_id}', Email: '{user_google_email}'"
    )

    # Download attachment content first, then optionally re-fetch message metadata
    # to resolve filename and MIME type for the saved file.
    try:
        attachment = await asyncio.to_thread(
            service.users()
            .messages()
            .attachments()
            .get(userId="me", messageId=message_id, id=attachment_id)
            .execute
        )
    except Exception as e:
        logger.error(
            f"[get_gmail_attachment_content] Failed to download attachment: {e}"
        )
        return (
            f"Error: Failed to download attachment. The attachment ID may have changed.\n"
            f"Please fetch the message content again to get an updated attachment ID.\n\n"
            f"Error details: {str(e)}"
        )

    # Format response with attachment data
    size_bytes = attachment.get("size", 0)
    size_kb = size_bytes / 1024 if size_bytes else 0
    base64_data = attachment.get("data", "")

    # Check if we're in stateless mode (can't save files)
    from auth.oauth_config import is_stateless_mode

    if is_stateless_mode():
        result_lines = [
            "Attachment downloaded successfully!",
            f"Message ID: {message_id}",
            f"Size: {size_kb:.1f} KB ({size_bytes} bytes)",
            "\n⚠️ Stateless mode: File storage disabled.",
            "\nBase64-encoded content (first 100 characters shown):",
            f"{base64_data[:100]}...",
            "\nNote: Attachment IDs are ephemeral. Always use IDs from the most recent message fetch.",
        ]
        logger.info(
            f"[get_gmail_attachment_content] Successfully downloaded {size_kb:.1f} KB attachment (stateless mode)"
        )
        return "\n".join(result_lines)

    # Save attachment to local disk and return file path
    try:
        from core.attachment_storage import get_attachment_storage, get_attachment_url
        from core.config import get_transport_mode

        storage = get_attachment_storage()

        # Try to get filename and mime type from message
        filename = None
        mime_type = None
        try:
            # Use format="full" with fields to limit response to attachment metadata only
            message_full = await asyncio.to_thread(
                service.users()
                .messages()
                .get(
                    userId="me",
                    id=message_id,
                    format="full",
                    fields="payload(parts(filename,mimeType,body(attachmentId,size)),body(attachmentId,size),filename,mimeType)",
                )
                .execute
            )
            payload = message_full.get("payload", {})
            attachments = _extract_attachments(payload)

            # First try exact attachmentId match
            for att in attachments:
                if att.get("attachmentId") == attachment_id:
                    filename = att.get("filename")
                    mime_type = att.get("mimeType")
                    break

            # Fallback: match by size if exactly one attachment matches (IDs are ephemeral)
            if not filename and attachments:
                size_matches = [
                    att
                    for att in attachments
                    if att.get("size") and abs(att["size"] - size_bytes) < 100
                ]
                if len(size_matches) == 1:
                    filename = size_matches[0].get("filename")
                    mime_type = size_matches[0].get("mimeType")
                    logger.warning(
                        f"Attachment {attachment_id} matched by size fallback as '{filename}'"
                    )

            # Last resort: if only one attachment, use its name
            if not filename and len(attachments) == 1:
                filename = attachments[0].get("filename")
                mime_type = attachments[0].get("mimeType")
        except Exception:
            logger.debug(
                f"Could not fetch attachment metadata for {attachment_id}, using defaults"
            )

        # Save attachment to local disk
        result = storage.save_attachment(
            base64_data=base64_data, filename=filename, mime_type=mime_type
        )

        result_lines = [
            "Attachment downloaded successfully!",
            f"Message ID: {message_id}",
            f"Filename: {filename or 'unknown'}",
            f"Size: {size_kb:.1f} KB ({size_bytes} bytes)",
        ]

        if get_transport_mode() == "stdio":
            result_lines.append(f"\n📎 Saved to: {result.path}")
            result_lines.append(
                "\nThe file has been saved to disk and can be accessed directly via the file path."
            )
        else:
            download_url = get_attachment_url(result.file_id)
            result_lines.append(f"\n📎 Download URL: {download_url}")
            result_lines.append("\nThe file will expire after 1 hour.")

        result_lines.append(
            "\nNote: Attachment IDs are ephemeral. Always use IDs from the most recent message fetch."
        )

        logger.info(
            f"[get_gmail_attachment_content] Successfully saved {size_kb:.1f} KB attachment to {result.path}"
        )
        return "\n".join(result_lines)

    except Exception as e:
        logger.error(
            f"[get_gmail_attachment_content] Failed to save attachment: {e}",
            exc_info=True,
        )
        # Fallback to showing base64 preview
        result_lines = [
            "Attachment downloaded successfully!",
            f"Message ID: {message_id}",
            f"Size: {size_kb:.1f} KB ({size_bytes} bytes)",
            "\n⚠️ Failed to save attachment file. Showing preview instead.",
            "\nBase64-encoded content (first 100 characters shown):",
            f"{base64_data[:100]}...",
            f"\nError: {str(e)}",
            "\nNote: Attachment IDs are ephemeral. Always use IDs from the most recent message fetch.",
        ]
        return "\n".join(result_lines)


@server.tool()
@handle_http_errors("send_gmail_message", service_type="gmail")
@require_google_service("gmail", GMAIL_SEND_SCOPE)
async def send_gmail_message(
    service,
    user_google_email: str,
    to: Annotated[str, Field(description="Recipient email address.")],
    subject: Annotated[str, Field(description="Email subject.")],
    body: Annotated[str, Field(description="Email body content (plain text or HTML).")],
    body_format: Annotated[
        Literal["plain", "html"],
        Field(
            description="Email body format. Use 'plain' for plaintext or 'html' for HTML content.",
        ),
    ] = "plain",
    cc: Annotated[
        Optional[str], Field(description="Optional CC email address.")
    ] = None,
    bcc: Annotated[
        Optional[str], Field(description="Optional BCC email address.")
    ] = None,
    from_name: Annotated[
        Optional[str],
        Field(
            description="Optional sender display name (e.g., 'Peter Hartree'). If provided, the From header will be formatted as 'Name <email>'.",
        ),
    ] = None,
    from_email: Annotated[
        Optional[str],
        Field(
            description="Optional 'Send As' alias email address. Must be configured in Gmail settings (Settings > Accounts > Send mail as). If not provided, uses the authenticated user's email.",
        ),
    ] = None,
    thread_id: Annotated[
        Optional[str],
        Field(
            description="Optional Gmail thread ID to reply within.",
        ),
    ] = None,
    in_reply_to: Annotated[
        Optional[str],
        Field(
            description="Optional RFC Message-ID of the message being replied to (e.g., '<message123@gmail.com>').",
        ),
    ] = None,
    references: Annotated[
        Optional[str],
        Field(
            description="Optional chain of Message-IDs for proper threading.",
        ),
    ] = None,
    attachments: Annotated[
        Optional[List[Dict[str, str]]],
        Field(
            description='Optional list of attachments. Each can have: "path" (file path, auto-encodes), OR "content" (standard base64, not urlsafe) + "filename". Optional "mime_type". Example: [{"path": "/path/to/file.pdf"}] or [{"filename": "doc.pdf", "content": "base64data", "mime_type": "application/pdf"}]',
        ),
    ] = None,
) -> str:
    """
    Sends an email using the user's Gmail account. Supports both new emails and replies with optional attachments.
    Supports Gmail's "Send As" feature to send from configured alias addresses.

    Args:
        to (str): Recipient email address.
        subject (str): Email subject.
        body (str): Email body content.
        body_format (Literal['plain', 'html']): Email body format. Defaults to 'plain'.
        attachments (Optional[List[Dict[str, str]]]): Optional list of attachments. Each dict can contain:
            Option 1 - File path (auto-encodes):
              - 'path' (required): File path to attach
              - 'filename' (optional): Override filename
              - 'mime_type' (optional): Override MIME type (auto-detected if not provided)
            Option 2 - Base64 content:
              - 'content' (required): Standard base64-encoded file content (not urlsafe)
              - 'filename' (required): Name of the file
              - 'mime_type' (optional): MIME type (defaults to 'application/octet-stream')
        cc (Optional[str]): Optional CC email address.
        bcc (Optional[str]): Optional BCC email address.
        from_name (Optional[str]): Optional sender display name. If provided, the From header will be formatted as 'Name <email>'.
        from_email (Optional[str]): Optional 'Send As' alias email address. The alias must be
            configured in Gmail settings (Settings > Accounts > Send mail as). If not provided,
            the email will be sent from the authenticated user's primary email address.
        user_google_email (str): The user's Google email address. Required for authentication.
        thread_id (Optional[str]): Optional Gmail thread ID to reply within. When provided, sends a reply.
        in_reply_to (Optional[str]): Optional RFC Message-ID of the message being replied to (e.g., '<message123@gmail.com>').
        references (Optional[str]): Optional chain of RFC Message-IDs for proper threading (e.g., '<msg1@gmail.com> <msg2@gmail.com>').

    Returns:
        str: Confirmation message with the sent email's message ID.

    Examples:
        # Send a new email
        send_gmail_message(to="user@example.com", subject="Hello", body="Hi there!")

        # Send with a custom display name
        send_gmail_message(to="user@example.com", subject="Hello", body="Hi there!", from_name="John Doe")

        # Send an HTML email
        send_gmail_message(
            to="user@example.com",
            subject="Hello",
            body="<strong>Hi there!</strong>",
            body_format="html"
        )

        # Send from a configured alias (Send As)
        send_gmail_message(
            to="user@example.com",
            subject="Business Inquiry",
            body="Hello from my business address...",
            from_email="business@mydomain.com"
        )

        # Send an email with CC and BCC
        send_gmail_message(
            to="user@example.com",
            cc="manager@example.com",
            bcc="archive@example.com",
            subject="Project Update",
            body="Here's the latest update..."
        )

        # Send an email with attachments (using file path)
        send_gmail_message(
            to="user@example.com",
            subject="Report",
            body="Please see attached report.",
            attachments=[{
                "path": "/path/to/report.pdf"
            }]
        )

        # Send an email with attachments (using base64 content)
        send_gmail_message(
            to="user@example.com",
            subject="Report",
            body="Please see attached report.",
            attachments=[{
                "filename": "report.pdf",
                "content": "JVBERi0xLjQK...",  # base64 encoded PDF
                "mime_type": "application/pdf"
            }]
        )

        # Send a reply
        send_gmail_message(
            to="user@example.com",
            subject="Re: Meeting tomorrow",
            body="Thanks for the update!",
            thread_id="thread_123",
            in_reply_to="<message123@gmail.com>",
            references="<original@gmail.com> <message123@gmail.com>"
        )
    """
    logger.info(
        f"[send_gmail_message] Invoked. Email: '{user_google_email}', Subject: '{subject}', Attachments: {len(attachments) if attachments else 0}"
    )

    # Prepare the email message
    # Use from_email (Send As alias) if provided, otherwise default to authenticated user
    sender_email = from_email or user_google_email
    raw_message, thread_id_final, attached_count = _prepare_gmail_message(
        subject=subject,
        body=body,
        to=to,
        cc=cc,
        bcc=bcc,
        thread_id=thread_id,
        in_reply_to=in_reply_to,
        references=references,
        body_format=body_format,
        from_email=sender_email,
        from_name=from_name,
        attachments=attachments if attachments else None,
    )

    requested_attachment_count = len(attachments or [])
    if requested_attachment_count > 0 and attached_count == 0:
        raise UserInputError(
            "No valid attachments were added. Verify each attachment path/content and retry."
        )

    send_body = {"raw": raw_message}

    # Associate with thread if provided
    if thread_id_final:
        send_body["threadId"] = thread_id_final

    # Send the message
    sent_message = await asyncio.to_thread(
        service.users().messages().send(userId="me", body=send_body).execute
    )
    message_id = sent_message.get("id")

    if requested_attachment_count > 0:
        attachment_info = _format_attachment_result(
            attached_count, requested_attachment_count
        )
        return f"Email sent{attachment_info}! Message ID: {message_id}"
    return f"Email sent! Message ID: {message_id}"


@server.tool()
@handle_http_errors("draft_gmail_message", service_type="gmail")
@require_google_service("gmail", GMAIL_COMPOSE_SCOPE)
async def draft_gmail_message(
    service,
    user_google_email: str,
    subject: Annotated[str, Field(description="Email subject.")],
    body: Annotated[str, Field(description="Email body (plain text).")],
    body_format: Annotated[
        Literal["plain", "html"],
        Field(
            description="Email body format. Use 'plain' for plaintext or 'html' for HTML content.",
        ),
    ] = "plain",
    to: Annotated[
        Optional[str],
        Field(
            description="Optional recipient email address.",
        ),
    ] = None,
    cc: Annotated[
        Optional[str], Field(description="Optional CC email address.")
    ] = None,
    bcc: Annotated[
        Optional[str], Field(description="Optional BCC email address.")
    ] = None,
    from_name: Annotated[
        Optional[str],
        Field(
            description="Optional sender display name (e.g., 'Peter Hartree'). If provided, the From header will be formatted as 'Name <email>'.",
        ),
    ] = None,
    from_email: Annotated[
        Optional[str],
        Field(
            description="Optional 'Send As' alias email address. Must be configured in Gmail settings (Settings > Accounts > Send mail as). If not provided, uses the authenticated user's email.",
        ),
    ] = None,
    thread_id: Annotated[
        Optional[str],
        Field(
            description="Optional Gmail thread ID to reply within.",
        ),
    ] = None,
    in_reply_to: Annotated[
        Optional[str],
        Field(
            description="Optional RFC Message-ID of the message being replied to (e.g., '<message123@gmail.com>').",
        ),
    ] = None,
    references: Annotated[
        Optional[str],
        Field(
            description="Optional chain of Message-IDs for proper threading.",
        ),
    ] = None,
    attachments: Annotated[
        Optional[List[Dict[str, str]]],
        Field(
            description="Optional list of attachments. Each can have: 'path' (file path, auto-encodes), OR 'content' (standard base64, not urlsafe) + 'filename'. Optional 'mime_type' (auto-detected from path if not provided).",
        ),
    ] = None,
    include_signature: Annotated[
        bool,
        Field(
            description="Whether to append the Gmail signature from Settings > Signature when available. Defaults to true.",
        ),
    ] = True,
    quote_original: Annotated[
        bool,
        Field(
            description="Whether to include the original message as a quoted reply. Requires thread_id. Defaults to false.",
        ),
    ] = False,
) -> str:
    """
    Creates a draft email in the user's Gmail account. Supports both new drafts and reply drafts with optional attachments.
    Supports Gmail's "Send As" feature to draft from configured alias addresses.

    Args:
        user_google_email (str): The user's Google email address. Required for authentication.
        subject (str): Email subject.
        body (str): Email body (plain text).
        body_format (Literal['plain', 'html']): Email body format. Defaults to 'plain'.
        to (Optional[str]): Optional recipient email address. Can be left empty for drafts.
        cc (Optional[str]): Optional CC email address.
        bcc (Optional[str]): Optional BCC email address.
        from_name (Optional[str]): Optional sender display name. If provided, the From header will be formatted as 'Name <email>'.
        from_email (Optional[str]): Optional 'Send As' alias email address. The alias must be
            configured in Gmail settings (Settings > Accounts > Send mail as). If not provided,
            the draft will be from the authenticated user's primary email address.
        thread_id (Optional[str]): Optional Gmail thread ID to reply within. When provided, creates a reply draft.
        in_reply_to (Optional[str]): Optional RFC Message-ID of the message being replied to (e.g., '<message123@gmail.com>').
        references (Optional[str]): Optional chain of RFC Message-IDs for proper threading (e.g., '<msg1@gmail.com> <msg2@gmail.com>').
        attachments (List[Dict[str, str]]): Optional list of attachments. Each dict can contain:
            Option 1 - File path (auto-encodes):
              - 'path' (required): File path to attach
              - 'filename' (optional): Override filename
              - 'mime_type' (optional): Override MIME type (auto-detected if not provided)
            Option 2 - Base64 content:
              - 'content' (required): Standard base64-encoded file content (not urlsafe)
              - 'filename' (required): Name of the file
              - 'mime_type' (optional): MIME type (defaults to 'application/octet-stream')
        include_signature (bool): Whether to append Gmail signature HTML from send-as settings.
            If unavailable (e.g., missing gmail.settings.basic scope), the draft is still created without signature.
        quote_original (bool): Whether to include the original message as a quoted reply.
            Requires thread_id to be provided. When enabled, fetches the original message
            and appends it below the signature. Defaults to False.

    Returns:
        str: Confirmation message with the created draft's ID.

    Examples:
        # Create a new draft
        draft_gmail_message(subject="Hello", body="Hi there!", to="user@example.com")

        # Create a draft from a configured alias (Send As)
        draft_gmail_message(
            subject="Business Inquiry",
            body="Hello from my business address...",
            to="user@example.com",
            from_email="business@mydomain.com"
        )

        # Create a plaintext draft with CC and BCC
        draft_gmail_message(
            subject="Project Update",
            body="Here's the latest update...",
            to="user@example.com",
            cc="manager@example.com",
            bcc="archive@example.com"
        )

        # Create a HTML draft with CC and BCC
        draft_gmail_message(
            subject="Project Update",
            body="<strong>Hi there!</strong>",
            body_format="html",
            to="user@example.com",
            cc="manager@example.com",
            bcc="archive@example.com"
        )

        # Create a reply draft in plaintext
        draft_gmail_message(
            subject="Re: Meeting tomorrow",
            body="Thanks for the update!",
            to="user@example.com",
            thread_id="thread_123",
            in_reply_to="<message123@gmail.com>",
            references="<original@gmail.com> <message123@gmail.com>"
        )

        # Create a reply draft in HTML
        draft_gmail_message(
            subject="Re: Meeting tomorrow",
            body="<strong>Thanks for the update!</strong>",
            body_format="html",
            to="user@example.com",
            thread_id="thread_123",
            in_reply_to="<message123@gmail.com>",
            references="<original@gmail.com> <message123@gmail.com>"
        )
    """
    logger.info(
        f"[draft_gmail_message] Invoked. Email: '{user_google_email}', Subject: '{subject}'"
    )

    # Prepare the email message
    # Use from_email (Send As alias) if provided, otherwise default to authenticated user
    sender_email = from_email or user_google_email
    draft_body = body
    signature_html = ""
    if include_signature:
        signature_html = await _get_send_as_signature_html(
            service, from_email=sender_email
        )

    if quote_original and thread_id:
        original = await _fetch_original_for_quote(service, thread_id, in_reply_to)
        if original:
            draft_body = _build_quoted_reply_body(
                draft_body, body_format, signature_html, original
            )
        else:
            draft_body = _append_signature_to_body(
                draft_body, body_format, signature_html
            )
    else:
        draft_body = _append_signature_to_body(draft_body, body_format, signature_html)

    # Auto-populate In-Reply-To and References when thread_id is provided
    # but headers are missing, to ensure the draft renders inline in Gmail
    if thread_id and (not in_reply_to or not references):
        thread_message_ids = await _fetch_thread_message_ids(service, thread_id)
        in_reply_to, references = _derive_reply_headers(
            thread_message_ids, in_reply_to, references
        )

    raw_message, thread_id_final, attached_count = _prepare_gmail_message(
        subject=subject,
        body=draft_body,
        body_format=body_format,
        to=to,
        cc=cc,
        bcc=bcc,
        thread_id=thread_id,
        in_reply_to=in_reply_to,
        references=references,
        from_email=sender_email,
        from_name=from_name,
        attachments=attachments,
    )

    requested_attachment_count = len(attachments or [])
    if requested_attachment_count > 0 and attached_count == 0:
        raise UserInputError(
            "No valid attachments were added. Verify each attachment path/content and retry."
        )

    # Create a draft instead of sending
    draft_body = {"message": {"raw": raw_message}}

    # Associate with thread if provided
    if thread_id_final:
        draft_body["message"]["threadId"] = thread_id_final

    # Create the draft
    created_draft = await asyncio.to_thread(
        service.users().drafts().create(userId="me", body=draft_body).execute
    )
    draft_id = created_draft.get("id")
    attachment_info = _format_attachment_result(
        attached_count, requested_attachment_count
    )
    return f"Draft created{attachment_info}! Draft ID: {draft_id}"


def _format_thread_content(thread_data: dict, thread_id: str) -> str:
    """
    Helper function to format thread content from Gmail API response.

    Args:
        thread_data (dict): Thread data from Gmail API
        thread_id (str): Thread ID for display

    Returns:
        str: Formatted thread content
    """
    messages = thread_data.get("messages", [])
    if not messages:
        return f"No messages found in thread '{thread_id}'."

    # Extract thread subject from the first message
    first_message = messages[0]
    first_headers = {
        h["name"]: h["value"]
        for h in first_message.get("payload", {}).get("headers", [])
    }
    thread_subject = first_headers.get("Subject", "(no subject)")

    # Build the thread content
    content_lines = [
        f"Thread ID: {thread_id}",
        f"Subject: {thread_subject}",
        f"Messages: {len(messages)}",
        "",
    ]

    # Process each message in the thread
    for i, message in enumerate(messages, 1):
        # Extract headers
        headers = {
            h["name"]: h["value"] for h in message.get("payload", {}).get("headers", [])
        }

        sender = headers.get("From", "(unknown sender)")
        date = headers.get("Date", "(unknown date)")
        subject = headers.get("Subject", "(no subject)")
        rfc822_message_id = headers.get("Message-ID", "")
        in_reply_to = headers.get("In-Reply-To", "")
        references = headers.get("References", "")

        # Extract both text and HTML bodies
        payload = message.get("payload", {})
        bodies = _extract_message_bodies(payload)
        text_body = bodies.get("text", "")
        html_body = bodies.get("html", "")

        # Format body content with HTML fallback
        body_data = _format_body_content(text_body, html_body)

        # Add message to content
        content_lines.extend(
            [
                f"=== Message {i} ===",
                f"From: {sender}",
                f"Date: {date}",
            ]
        )

        if rfc822_message_id:
            content_lines.append(f"Message-ID: {rfc822_message_id}")
        if in_reply_to:
            content_lines.append(f"In-Reply-To: {in_reply_to}")
        if references:
            content_lines.append(f"References: {references}")

        # Only show subject if it's different from thread subject
        if subject != thread_subject:
            content_lines.append(f"Subject: {subject}")

        content_lines.extend(
            [
                "",
                body_data,
                "",
            ]
        )

    return "\n".join(content_lines)


@server.tool()
@require_google_service("gmail", "gmail_read")
@handle_http_errors("get_gmail_thread_content", is_read_only=True, service_type="gmail")
async def get_gmail_thread_content(
    service, thread_id: str, user_google_email: str
) -> str:
    """
    Retrieves the complete content of a Gmail conversation thread, including all messages.

    Args:
        thread_id (str): The unique ID of the Gmail thread to retrieve.
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: The complete thread content with all messages formatted for reading.
    """
    logger.info(
        f"[get_gmail_thread_content] Invoked. Thread ID: '{thread_id}', Email: '{user_google_email}'"
    )

    # Fetch the complete thread with all messages
    thread_response = await asyncio.to_thread(
        service.users().threads().get(userId="me", id=thread_id, format="full").execute
    )

    return _format_thread_content(thread_response, thread_id)


@server.tool()
@require_google_service("gmail", "gmail_read")
@handle_http_errors(
    "get_gmail_threads_content_batch", is_read_only=True, service_type="gmail"
)
async def get_gmail_threads_content_batch(
    service,
    thread_ids: List[str],
    user_google_email: str,
) -> str:
    """
    Retrieves the content of multiple Gmail threads in a single batch request.
    Supports up to 25 threads per batch to prevent SSL connection exhaustion.

    Args:
        thread_ids (List[str]): A list of Gmail thread IDs to retrieve. The function will automatically batch requests in chunks of 25.
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: A formatted list of thread contents with separators.
    """
    logger.info(
        f"[get_gmail_threads_content_batch] Invoked. Thread count: {len(thread_ids)}, Email: '{user_google_email}'"
    )

    if not thread_ids:
        raise ValueError("No thread IDs provided")

    output_threads = []

    def _batch_callback(request_id, response, exception):
        """Callback for batch requests"""
        results[request_id] = {"data": response, "error": exception}

    # Process in smaller chunks to prevent SSL connection exhaustion
    for chunk_start in range(0, len(thread_ids), GMAIL_BATCH_SIZE):
        chunk_ids = thread_ids[chunk_start : chunk_start + GMAIL_BATCH_SIZE]
        results: Dict[str, Dict] = {}

        # Try to use batch API
        try:
            batch = service.new_batch_http_request(callback=_batch_callback)

            for tid in chunk_ids:
                req = service.users().threads().get(userId="me", id=tid, format="full")
                batch.add(req, request_id=tid)

            # Execute batch request
            await asyncio.to_thread(batch.execute)

        except Exception as batch_error:
            # Fallback to sequential processing instead of parallel to prevent SSL exhaustion
            logger.warning(
                f"[get_gmail_threads_content_batch] Batch API failed, falling back to sequential processing: {batch_error}"
            )

            async def fetch_thread_with_retry(tid: str, max_retries: int = 3):
                """Fetch a single thread with exponential backoff retry for SSL errors"""
                for attempt in range(max_retries):
                    try:
                        thread = await asyncio.to_thread(
                            service.users()
                            .threads()
                            .get(userId="me", id=tid, format="full")
                            .execute
                        )
                        return tid, thread, None
                    except ssl.SSLError as ssl_error:
                        if attempt < max_retries - 1:
                            # Exponential backoff: 1s, 2s, 4s
                            delay = 2**attempt
                            logger.warning(
                                f"[get_gmail_threads_content_batch] SSL error for thread {tid} on attempt {attempt + 1}: {ssl_error}. Retrying in {delay}s..."
                            )
                            await asyncio.sleep(delay)
                        else:
                            logger.error(
                                f"[get_gmail_threads_content_batch] SSL error for thread {tid} on final attempt: {ssl_error}"
                            )
                            return tid, None, ssl_error
                    except Exception as e:
                        return tid, None, e

            # Process threads sequentially with small delays to prevent connection exhaustion
            for tid in chunk_ids:
                tid_result, thread_data, error = await fetch_thread_with_retry(tid)
                results[tid_result] = {"data": thread_data, "error": error}
                # Brief delay between requests to allow connection cleanup
                await asyncio.sleep(GMAIL_REQUEST_DELAY)

        # Process results for this chunk
        for tid in chunk_ids:
            entry = results.get(tid, {"data": None, "error": "No result"})

            if entry["error"]:
                output_threads.append(f"⚠️ Thread {tid}: {entry['error']}\n")
            else:
                thread = entry["data"]
                if not thread:
                    output_threads.append(f"⚠️ Thread {tid}: No data returned\n")
                    continue

                output_threads.append(_format_thread_content(thread, tid))

    # Combine all threads with separators
    header = f"Retrieved {len(thread_ids)} threads:"
    return header + "\n\n" + "\n---\n\n".join(output_threads)


@server.tool()
@handle_http_errors("list_gmail_labels", is_read_only=True, service_type="gmail")
@require_google_service("gmail", "gmail_read")
async def list_gmail_labels(service, user_google_email: str) -> str:
    """
    Lists all labels in the user's Gmail account.

    Args:
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: A formatted list of all labels with their IDs, names, and types.
    """
    logger.info(f"[list_gmail_labels] Invoked. Email: '{user_google_email}'")

    response = await asyncio.to_thread(
        service.users().labels().list(userId="me").execute
    )
    labels = response.get("labels", [])

    if not labels:
        return "No labels found."

    lines = [f"Found {len(labels)} labels:", ""]

    system_labels = []
    user_labels = []

    for label in labels:
        if label.get("type") == "system":
            system_labels.append(label)
        else:
            user_labels.append(label)

    if system_labels:
        lines.append("📂 SYSTEM LABELS:")
        for label in system_labels:
            lines.append(f"  • {label['name']} (ID: {label['id']})")
        lines.append("")

    if user_labels:
        lines.append("🏷️  USER LABELS:")
        for label in user_labels:
            lines.append(f"  • {label['name']} (ID: {label['id']})")

    return "\n".join(lines)


@server.tool()
@handle_http_errors("manage_gmail_label", service_type="gmail")
@require_google_service("gmail", GMAIL_LABELS_SCOPE)
async def manage_gmail_label(
    service,
    user_google_email: str,
    action: Literal["create", "update", "delete"],
    name: Optional[str] = None,
    label_id: Optional[str] = None,
    label_list_visibility: Literal["labelShow", "labelHide"] = "labelShow",
    message_list_visibility: Literal["show", "hide"] = "show",
) -> str:
    """
    Manages Gmail labels: create, update, or delete labels.

    Args:
        user_google_email (str): The user's Google email address. Required.
        action (Literal["create", "update", "delete"]): Action to perform on the label.
        name (Optional[str]): Label name. Required for create, optional for update.
        label_id (Optional[str]): Label ID. Required for update and delete operations.
        label_list_visibility (Literal["labelShow", "labelHide"]): Whether the label is shown in the label list.
        message_list_visibility (Literal["show", "hide"]): Whether the label is shown in the message list.

    Returns:
        str: Confirmation message of the label operation.
    """
    logger.info(
        f"[manage_gmail_label] Invoked. Email: '{user_google_email}', Action: '{action}'"
    )

    if action == "create" and not name:
        raise Exception("Label name is required for create action.")

    if action in ["update", "delete"] and not label_id:
        raise Exception("Label ID is required for update and delete actions.")

    if action == "create":
        label_object = {
            "name": name,
            "labelListVisibility": label_list_visibility,
            "messageListVisibility": message_list_visibility,
        }
        created_label = await asyncio.to_thread(
            service.users().labels().create(userId="me", body=label_object).execute
        )
        return f"Label created successfully!\nName: {created_label['name']}\nID: {created_label['id']}"

    elif action == "update":
        current_label = await asyncio.to_thread(
            service.users().labels().get(userId="me", id=label_id).execute
        )

        label_object = {
            "id": label_id,
            "name": name if name is not None else current_label["name"],
            "labelListVisibility": label_list_visibility,
            "messageListVisibility": message_list_visibility,
        }

        updated_label = await asyncio.to_thread(
            service.users()
            .labels()
            .update(userId="me", id=label_id, body=label_object)
            .execute
        )
        return f"Label updated successfully!\nName: {updated_label['name']}\nID: {updated_label['id']}"

    elif action == "delete":
        label = await asyncio.to_thread(
            service.users().labels().get(userId="me", id=label_id).execute
        )
        label_name = label["name"]

        await asyncio.to_thread(
            service.users().labels().delete(userId="me", id=label_id).execute
        )
        return f"Label '{label_name}' (ID: {label_id}) deleted successfully!"


@server.tool()
@handle_http_errors("list_gmail_filters", is_read_only=True, service_type="gmail")
@require_google_service("gmail", "gmail_settings_basic")
async def list_gmail_filters(service, user_google_email: str) -> str:
    """
    Lists all Gmail filters configured in the user's mailbox.

    Args:
        user_google_email (str): The user's Google email address. Required.

    Returns:
        str: A formatted list of filters with their criteria and actions.
    """
    logger.info(f"[list_gmail_filters] Invoked. Email: '{user_google_email}'")

    response = await asyncio.to_thread(
        service.users().settings().filters().list(userId="me").execute
    )

    filters = response.get("filter") or response.get("filters") or []

    if not filters:
        return "No filters found."

    lines = [f"Found {len(filters)} filters:", ""]

    for filter_obj in filters:
        filter_id = filter_obj.get("id", "(no id)")
        criteria = filter_obj.get("criteria", {})
        action = filter_obj.get("action", {})

        lines.append(f"🔹 Filter ID: {filter_id}")
        lines.append("  Criteria:")

        criteria_lines = []
        if criteria.get("from"):
            criteria_lines.append(f"From: {criteria['from']}")
        if criteria.get("to"):
            criteria_lines.append(f"To: {criteria['to']}")
        if criteria.get("subject"):
            criteria_lines.append(f"Subject: {criteria['subject']}")
        if criteria.get("query"):
            criteria_lines.append(f"Query: {criteria['query']}")
        if criteria.get("negatedQuery"):
            criteria_lines.append(f"Exclude Query: {criteria['negatedQuery']}")
        if criteria.get("hasAttachment"):
            criteria_lines.append("Has attachment")
        if criteria.get("excludeChats"):
            criteria_lines.append("Exclude chats")
        if criteria.get("size"):
            comparison = criteria.get("sizeComparison", "")
            criteria_lines.append(
                f"Size {comparison or ''} {criteria['size']} bytes".strip()
            )

        if not criteria_lines:
            criteria_lines.append("(none)")

        lines.extend([f"    • {line}" for line in criteria_lines])

        lines.append("  Actions:")
        action_lines = []
        if action.get("forward"):
            action_lines.append(f"Forward to: {action['forward']}")
        if action.get("removeLabelIds"):
            action_lines.append(f"Remove labels: {', '.join(action['removeLabelIds'])}")
        if action.get("addLabelIds"):
            action_lines.append(f"Add labels: {', '.join(action['addLabelIds'])}")

        if not action_lines:
            action_lines.append("(none)")

        lines.extend([f"    • {line}" for line in action_lines])
        lines.append("")

    return "\n".join(lines).rstrip()


@server.tool()
@handle_http_errors("manage_gmail_filter", service_type="gmail")
@require_google_service("gmail", "gmail_settings_basic")
async def manage_gmail_filter(
    service,
    user_google_email: str,
    action: str,
    criteria: Optional[Dict[str, Any]] = None,
    filter_action: Optional[Dict[str, Any]] = None,
    filter_id: Optional[str] = None,
) -> str:
    """
    Manages Gmail filters. Supports creating and deleting filters.

    Args:
        user_google_email (str): The user's Google email address. Required.
        action (str): Action to perform - "create" or "delete".
        criteria (Optional[Dict[str, Any]]): Filter criteria object (required for create).
        filter_action (Optional[Dict[str, Any]]): Filter action object (required for create). Named 'filter_action' to avoid shadowing the 'action' parameter.
        filter_id (Optional[str]): ID of the filter to delete (required for delete).

    Returns:
        str: Confirmation message with filter details.
    """
    action_lower = action.lower().strip()
    if action_lower == "create":
        if not criteria or not filter_action:
            raise ValueError(
                "criteria and filter_action are required for create action"
            )
        logger.info("[manage_gmail_filter] Creating filter")
        filter_body = {"criteria": criteria, "action": filter_action}
        created_filter = await asyncio.to_thread(
            service.users()
            .settings()
            .filters()
            .create(userId="me", body=filter_body)
            .execute
        )
        fid = created_filter.get("id", "(unknown)")
        return f"Filter created successfully!\nFilter ID: {fid}"
    elif action_lower == "delete":
        if not filter_id:
            raise ValueError("filter_id is required for delete action")
        logger.info(f"[manage_gmail_filter] Deleting filter {filter_id}")
        filter_details = await asyncio.to_thread(
            service.users().settings().filters().get(userId="me", id=filter_id).execute
        )
        await asyncio.to_thread(
            service.users()
            .settings()
            .filters()
            .delete(userId="me", id=filter_id)
            .execute
        )
        criteria_info = filter_details.get("criteria", {})
        action_info = filter_details.get("action", {})
        return (
            "Filter deleted successfully!\n"
            f"Filter ID: {filter_id}\n"
            f"Criteria: {criteria_info or '(none)'}\n"
            f"Action: {action_info or '(none)'}"
        )
    else:
        raise ValueError(
            f"Invalid action '{action_lower}'. Must be 'create' or 'delete'."
        )


@server.tool()
@handle_http_errors("modify_gmail_message_labels", service_type="gmail")
@require_google_service("gmail", GMAIL_MODIFY_SCOPE)
async def modify_gmail_message_labels(
    service,
    user_google_email: str,
    message_id: str,
    add_label_ids: Optional[List[str]] = None,
    remove_label_ids: Optional[List[str]] = None,
) -> str:
    """
    Adds or removes labels from a Gmail message.
    To archive an email, remove the INBOX label.
    To delete an email, add the TRASH label.

    Args:
        user_google_email (str): The user's Google email address. Required.
        message_id (str): The ID of the message to modify.
        add_label_ids (Optional[List[str]]): List of label IDs to add to the message.
        remove_label_ids (Optional[List[str]]): List of label IDs to remove from the message.

    Returns:
        str: Confirmation message of the label changes applied to the message.
    """
    logger.info(
        f"[modify_gmail_message_labels] Invoked. Email: '{user_google_email}', Message ID: '{message_id}'"
    )

    if not add_label_ids and not remove_label_ids:
        raise Exception(
            "At least one of add_label_ids or remove_label_ids must be provided."
        )

    body = {}
    if add_label_ids:
        body["addLabelIds"] = add_label_ids
    if remove_label_ids:
        body["removeLabelIds"] = remove_label_ids

    await asyncio.to_thread(
        service.users().messages().modify(userId="me", id=message_id, body=body).execute
    )

    actions = []
    if add_label_ids:
        actions.append(f"Added labels: {', '.join(add_label_ids)}")
    if remove_label_ids:
        actions.append(f"Removed labels: {', '.join(remove_label_ids)}")

    return f"Message labels updated successfully!\nMessage ID: {message_id}\n{'; '.join(actions)}"


@server.tool()
@handle_http_errors("batch_modify_gmail_message_labels", service_type="gmail")
@require_google_service("gmail", GMAIL_MODIFY_SCOPE)
async def batch_modify_gmail_message_labels(
    service,
    user_google_email: str,
    message_ids: List[str],
    add_label_ids: Optional[List[str]] = None,
    remove_label_ids: Optional[List[str]] = None,
) -> str:
    """
    Adds or removes labels from multiple Gmail messages in a single batch request.

    Args:
        user_google_email (str): The user's Google email address. Required.
        message_ids (List[str]): A list of message IDs to modify.
        add_label_ids (Optional[List[str]]): List of label IDs to add to the messages.
        remove_label_ids (Optional[List[str]]): List of label IDs to remove from the messages.

    Returns:
        str: Confirmation message of the label changes applied to the messages.
    """
    logger.info(
        f"[batch_modify_gmail_message_labels] Invoked. Email: '{user_google_email}', Message IDs: '{message_ids}'"
    )

    if not add_label_ids and not remove_label_ids:
        raise Exception(
            "At least one of add_label_ids or remove_label_ids must be provided."
        )

    body = {"ids": message_ids}
    if add_label_ids:
        body["addLabelIds"] = add_label_ids
    if remove_label_ids:
        body["removeLabelIds"] = remove_label_ids

    await asyncio.to_thread(
        service.users().messages().batchModify(userId="me", body=body).execute
    )

    actions = []
    if add_label_ids:
        actions.append(f"Added labels: {', '.join(add_label_ids)}")
    if remove_label_ids:
        actions.append(f"Removed labels: {', '.join(remove_label_ids)}")

    return f"Labels updated for {len(message_ids)} messages: {'; '.join(actions)}"