const Database = require('better-sqlite3');
const path = require('path');
const fs = require('fs');

/**
 * Migration System for BREEDR
 * Automatically runs on startup to ensure schema is correct
 */

class MigrationRunner {
  constructor(dbPath) {
    this.dbPath = dbPath;
    this.db = null;
  }

  connect() {
    this.db = new Database(this.dbPath);
    this.db.pragma('foreign_keys = ON');
  }

  close() {
    if (this.db) {
      this.db.close();
    }
  }

  // Get current schema version from database
  getSchemaVersion() {
    try {
      const result = this.db.prepare('SELECT version FROM schema_version ORDER BY version DESC LIMIT 1').get();
      return result ? result.version : 0;
    } catch (error) {
      // schema_version table doesn't exist, create it
      this.db.exec(`
        CREATE TABLE IF NOT EXISTS schema_version (
          version INTEGER PRIMARY KEY,
          applied_at DATETIME DEFAULT CURRENT_TIMESTAMP,
          description TEXT
        )
      `);
      return 0;
    }
  }

  // Record migration completion
  recordMigration(version, description) {
    this.db.prepare('INSERT OR IGNORE INTO schema_version (version, description) VALUES (?, ?)').run(version, description);
  }

  // Check if dogs table has old sire/dam columns
  hasOldSchema() {
    const columns = this.db.prepare("PRAGMA table_info(dogs)").all();
    return columns.some(col => col.name === 'sire' || col.name === 'dam');
  }

  // Check if litter_id column exists
  hasLitterIdColumn() {
    const columns = this.db.prepare("PRAGMA table_info(dogs)").all();
    return columns.some(col => col.name === 'litter_id');
  }

  // Migration 1: Remove sire/dam columns, use parents table
  migration001_removeOldParentColumns() {
    console.log('[Migration 001] Checking for old sire/dam columns...');
    
    if (!this.hasOldSchema()) {
      console.log('[Migration 001] Schema is already correct, skipping');
      return;
    }

    console.log('[Migration 001] Found old schema with sire/dam columns');
    console.log('[Migration 001] Migrating to parents table...');

    this.db.exec('BEGIN TRANSACTION');

    try {
      // Ensure parents table exists
      this.db.exec(`
        CREATE TABLE IF NOT EXISTS parents (
          id INTEGER PRIMARY KEY AUTOINCREMENT,
          dog_id INTEGER NOT NULL,
          parent_id INTEGER NOT NULL,
          parent_type TEXT NOT NULL CHECK(parent_type IN ('sire', 'dam')),
          FOREIGN KEY (dog_id) REFERENCES dogs(id) ON DELETE CASCADE,
          FOREIGN KEY (parent_id) REFERENCES dogs(id) ON DELETE CASCADE,
          UNIQUE(dog_id, parent_type)
        );
        
        CREATE INDEX IF NOT EXISTS idx_parents_dog ON parents(dog_id);
        CREATE INDEX IF NOT EXISTS idx_parents_parent ON parents(parent_id);
      `);

      // Backup current dogs table
      this.db.exec('DROP TABLE IF EXISTS dogs_migration_backup');
      this.db.exec('CREATE TABLE dogs_migration_backup AS SELECT * FROM dogs');
      
      const backupCount = this.db.prepare('SELECT COUNT(*) as count FROM dogs_migration_backup').get();
      console.log(`[Migration 001] Backed up ${backupCount.count} dogs`);

      // Migrate parent relationships to parents table
      const columns = this.db.prepare("PRAGMA table_info(dogs_migration_backup)").all();
      const hasSire = columns.some(col => col.name === 'sire');
      const hasDam = columns.some(col => col.name === 'dam');
      const hasLitterId = columns.some(col => col.name === 'litter_id');

      if (hasSire) {
        const sireResult = this.db.prepare(`
          INSERT OR IGNORE INTO parents (dog_id, parent_id, parent_type)
          SELECT id, sire, 'sire' FROM dogs_migration_backup WHERE sire IS NOT NULL
        `).run();
        console.log(`[Migration 001] Migrated ${sireResult.changes} sire relationships`);
      }

      if (hasDam) {
        const damResult = this.db.prepare(`
          INSERT OR IGNORE INTO parents (dog_id, parent_id, parent_type)
          SELECT id, dam, 'dam' FROM dogs_migration_backup WHERE dam IS NOT NULL
        `).run();
        console.log(`[Migration 001] Migrated ${damResult.changes} dam relationships`);
      }

      // Drop old dogs table
      this.db.exec('DROP TABLE dogs');
      console.log('[Migration 001] Dropped old dogs table');

      // Create new dogs table with correct schema
      this.db.exec(`
        CREATE TABLE dogs (
          id INTEGER PRIMARY KEY AUTOINCREMENT,
          name TEXT NOT NULL,
          registration_number TEXT,
          microchip TEXT,
          sex TEXT CHECK(sex IN ('male', 'female')),
          birth_date DATE,
          breed TEXT,
          color TEXT,
          weight REAL,
          height REAL,
          notes TEXT,
          litter_id INTEGER,
          photo_urls TEXT,
          is_active INTEGER DEFAULT 1,
          created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
          updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
          FOREIGN KEY (litter_id) REFERENCES litters(id) ON DELETE SET NULL
        )
      `);
      console.log('[Migration 001] Created new dogs table');

      // Restore data (excluding sire/dam columns)
      const columnList = ['id', 'name', 'registration_number', 'microchip', 'sex', 'birth_date', 'breed', 'color', 'weight', 'height', 'notes', 'photo_urls', 'is_active', 'created_at', 'updated_at'];
      if (hasLitterId) {
        columnList.splice(11, 0, 'litter_id'); // Insert after notes
      }

      const columnsStr = columnList.join(', ');
      this.db.exec(`INSERT INTO dogs (${columnsStr}) SELECT ${columnsStr} FROM dogs_migration_backup`);
      
      const restoredCount = this.db.prepare('SELECT COUNT(*) as count FROM dogs').get();
      console.log(`[Migration 001] Restored ${restoredCount.count} dogs`);

      // Create indexes
      this.db.exec(`
        CREATE UNIQUE INDEX IF NOT EXISTS idx_dogs_microchip 
        ON dogs(microchip) WHERE microchip IS NOT NULL;
        
        CREATE INDEX IF NOT EXISTS idx_dogs_name ON dogs(name);
        CREATE INDEX IF NOT EXISTS idx_dogs_registration ON dogs(registration_number);
      `);

      // Clean up backup
      this.db.exec('DROP TABLE dogs_migration_backup');

      this.db.exec('COMMIT');
      console.log('[Migration 001] ✓ Migration complete!');

    } catch (error) {
      this.db.exec('ROLLBACK');
      console.error('[Migration 001] ✗ Migration failed:', error.message);
      throw error;
    }
  }

  // Migration 2: Add litter_id column if missing
  migration002_addLitterIdColumn() {
    console.log('[Migration 002] Checking for litter_id column...');
    
    if (this.hasLitterIdColumn()) {
      console.log('[Migration 002] litter_id column already exists, skipping');
      return;
    }

    console.log('[Migration 002] Adding litter_id column...');

    try {
      this.db.exec(`
        ALTER TABLE dogs ADD COLUMN litter_id INTEGER 
        REFERENCES litters(id) ON DELETE SET NULL
      `);
      console.log('[Migration 002] ✓ litter_id column added');
    } catch (error) {
      console.error('[Migration 002] ✗ Failed to add litter_id:', error.message);
      throw error;
    }
  }

  // Validate final schema
  validateSchema() {
    console.log('[Validation] Checking database schema...');

    const checks = [
      {
        name: 'Dogs table exists',
        test: () => {
          const tables = this.db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='dogs'").all();
          return tables.length > 0;
        }
      },
      {
        name: 'Dogs table has no sire/dam columns',
        test: () => {
          const columns = this.db.prepare("PRAGMA table_info(dogs)").all();
          return !columns.some(col => col.name === 'sire' || col.name === 'dam');
        }
      },
      {
        name: 'Parents table exists',
        test: () => {
          const tables = this.db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='parents'").all();
          return tables.length > 0;
        }
      },
      {
        name: 'Litter_id column exists',
        test: () => this.hasLitterIdColumn()
      },
      {
        name: 'Litters table exists',
        test: () => {
          const tables = this.db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='litters'").all();
          return tables.length > 0;
        }
      }
    ];

    let allPassed = true;
    checks.forEach(check => {
      const passed = check.test();
      const status = passed ? '✓' : '✗';
      console.log(`[Validation] ${status} ${check.name}`);
      if (!passed) allPassed = false;
    });

    if (allPassed) {
      console.log('[Validation] ✓ All schema checks passed!');
    } else {
      console.warn('[Validation] ⚠ Some schema checks failed');
    }

    return allPassed;
  }

  // Run all migrations
  runMigrations() {
    console.log('\n' + '='.repeat(60));
    console.log('BREEDR Database Migration System');
    console.log('='.repeat(60));
    console.log(`Database: ${this.dbPath}\n`);

    this.connect();

    try {
      const currentVersion = this.getSchemaVersion();
      console.log(`Current schema version: ${currentVersion}\n`);

      // Run migrations in order
      if (currentVersion < 1) {
        this.migration001_removeOldParentColumns();
        this.recordMigration(1, 'Migrate sire/dam columns to parents table');
      }

      if (currentVersion < 2) {
        this.migration002_addLitterIdColumn();
        this.recordMigration(2, 'Add litter_id column to dogs table');
      }

      // Validate final schema
      console.log('');
      const isValid = this.validateSchema();

      const finalVersion = this.getSchemaVersion();
      console.log('\n' + '='.repeat(60));
      console.log(`Schema version: ${currentVersion} → ${finalVersion}`);
      console.log('Migration system complete!');
      console.log('='.repeat(60) + '\n');

      return isValid;

    } catch (error) {
      console.error('\n✗ Migration system failed:', error.message);
      console.error(error.stack);
      throw error;
    } finally {
      this.close();
    }
  }
}

// Function to run migrations
function runMigrations(dbPath) {
  const runner = new MigrationRunner(dbPath);
  return runner.runMigrations();
}

module.exports = { MigrationRunner, runMigrations };

// Run migrations if called directly
if (require.main === module) {
  const dbPath = process.env.DB_PATH || path.join(__dirname, '../../data/breedr.db');
  runMigrations(dbPath);
}