# PNGer Development & Technical Instructions

## Project Overview

PNGer is a single-container web application for PNG editing and resizing, designed for deployment on Unraid with Gitea version control. It features a modern Svelte frontend and a high-performance Node.js/Sharp backend.

## Technical Architecture

### Architecture Overview

PNGer uses a multi-layered architecture designed for responsiveness and efficiency:

```mermaid
graph TD
    A[User Browser] --> B[Svelte Frontend]
    B --> C[Canvas API (Live Preview)]
    B --> D[Express API (Backend)]
    D --> E[Sharp Image Library]
    D --> F[Runtime Environment (Docker)]
```

### Backend (Express + Sharp)

The backend is built with Node.js and TypeScript, using Express for the API and Sharp for high-performance image processing.

**Key Endpoints:**
- `POST /api/transform` - Transform image (resize, crop, compress, convert)
- `GET /api/health` - Health check

**Key Dependencies:**
- `sharp`: High-performance image processing (handles resizing, cropping, and format conversion).
- `multer`: Middleware for handling `multipart/form-data`, used for file uploads.
- `express`: Web framework for the API.

### Frontend (Svelte + Vite)

The frontend is a reactive Svelte application that prioritizes real-time feedback and UX.

**Core Components & Modules:**
- `App.svelte`: Main application container managing state and UI.
- `lib/api.ts`: API client for backend communication.
- `lib/preview.ts`: Client-side preview logic using the Canvas API for instant feedback.
- `lib/theme.ts`: Dark/light theme management with persistent storage.
- `lib/presets.ts`: Configuration for smart image presets.

### Design System (Dark/Light Modes)

The UI uses a modern design system with CSS custom properties for theming:
- **Light Mode**: Clean white background with dark gold (`#b8860b`) accents.
- **Dark Mode**: Deep black (`#0a0a0a`) background with light gold (`#daa520`) accents.
- **Transparencies**: Dark/Light toggling allows users to inspect PNG transparency against different backgrounds.

## Implementation Details

### Live Preview System

Live preview is implemented using a client-side Canvas-based approach to provide instant feedback (< 100ms) without server round-trips.

**How it works:**
1. User uploads an image.
2. The browser loads the image into an HTML5 Canvas.
3. On any parameter change (width, quality, etc.), a debounced (300ms) update applies transformations to the canvas.
4. The canvas content is displayed side-by-side with the original for comparison.
5. File sizes are estimated from the Canvas data URL to provide immediate feedback on optimization savings.

### Docker Strategy & Fixes

PNGer uses a multi-stage Docker build to minimize image size and maximize security.

**Optimization Fixes applied:**
- **Dependency Installation**: Uses `npm install` instead of `npm ci` to handle missing lockfiles gracefully while maintaining stability via caret ranges in `package.json`.
- **Security**: Runs as a non-root `node` user in the final Alpine-based image.
- **Multer Upgrade**: Upgraded to `v2.1.0` for improved security and performance.

## Local Development Setup

### Prerequisites
- Node.js 20+
- npm or pnpm
- Docker (optional)

### Setup Steps

```bash
# Clone repository
git clone https://git.alwisp.com/jason/pnger.git
cd pnger

# Setup backend
cd backend
npm install
npm run dev

# Setup frontend (separate terminal)
cd frontend
npm install
npm run dev
```

### Environment Variables

**Backend (.env):**
- `PORT`: 3000 (internal)
- `MAX_FILE_SIZE`: 10485760 (10MB default)
- `CORS_ORIGIN`: http://localhost:5173

**Frontend (.env):**
- `VITE_API_URL`: http://localhost:3000/api

## Development Workflow & Standards

### Workflow
1. **Feature Branch**: Create from `main`.
2. **Develop**: Use hot-reload (`npm run dev`).
3. **Test**: Perform manual testing of image operations and presets.
4. **Commit**: Use `type: description` format (e.g., `feat: add rotation`).
5. **Merge**: Merge into `main` after review.

### Code Standards
- **TypeScript**: Use strict types where possible.
- **Svelte**: Keep components modular and under 300 lines.
- **Async/Await**: Use for all asynchronous operations.
- **Semantic HTML**: Ensure accessibility and proper structure.

## Troubleshooting

- **Port in use**: `lsof -ti:3000 | xargs kill -9`
- **Sharp issues**: `npm rebuild sharp`
- **Docker Cache**: `docker builder prune` if builds fail unexpectedly.
- **Preview Glitches**: Check browser console for Canvas API errors.

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**Last Updated**: March 12, 2026