/**
 * Auto-Migration System
 *
 * Runs SQL migration files from the migrations/ folder automatically on server startup.
 * Uses a schema_migrations table to track which migrations have been applied.
 *
 * Safe to run multiple times - only applies new migrations.
 */

import { Pool } from 'pg';
import fs from 'fs';
import path from 'path';

const MIGRATIONS_DIR = path.join(__dirname, '../../migrations');

/**
 * Ensure schema_migrations table exists
 */
async function ensureMigrationsTable(pool: Pool): Promise<void> {
  await pool.query(`
    CREATE TABLE IF NOT EXISTS schema_migrations (
      id SERIAL PRIMARY KEY,
      name VARCHAR(255) UNIQUE NOT NULL,
      applied_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
    )
  `);
}

/**
 * Get list of already-applied migrations
 */
async function getAppliedMigrations(pool: Pool): Promise<Set<string>> {
  const result = await pool.query('SELECT name FROM schema_migrations');
  return new Set(result.rows.map(row => row.name));
}

/**
 * Get list of migration files from disk
 */
function getMigrationFiles(): string[] {
  if (!fs.existsSync(MIGRATIONS_DIR)) {
    console.log('[AutoMigrate] No migrations directory found');
    return [];
  }

  return fs.readdirSync(MIGRATIONS_DIR)
    .filter(f => f.endsWith('.sql'))
    .sort(); // Sort alphabetically (001_, 002_, etc.)
}

/**
 * Run a single migration file
 */
async function runMigration(pool: Pool, filename: string): Promise<void> {
  const filepath = path.join(MIGRATIONS_DIR, filename);
  const sql = fs.readFileSync(filepath, 'utf8');

  const client = await pool.connect();
  try {
    await client.query('BEGIN');

    // Run the migration SQL
    await client.query(sql);

    // Record that this migration was applied
    await client.query(
      'INSERT INTO schema_migrations (name) VALUES ($1) ON CONFLICT (name) DO NOTHING',
      [filename]
    );

    await client.query('COMMIT');
    console.log(`[AutoMigrate] ✓ Applied: ${filename}`);
  } catch (error: any) {
    await client.query('ROLLBACK');
    console.error(`[AutoMigrate] ✗ Failed: ${filename}`);
    throw error;
  } finally {
    client.release();
  }
}

/**
 * Run all pending migrations
 *
 * @param pool - Database connection pool
 * @returns Number of migrations applied
 */
export async function runAutoMigrations(pool: Pool): Promise<number> {
  console.log('[AutoMigrate] Checking for pending migrations...');

  try {
    // Ensure migrations table exists
    await ensureMigrationsTable(pool);

    // Get applied and available migrations
    const applied = await getAppliedMigrations(pool);
    const available = getMigrationFiles();

    // Find pending migrations
    const pending = available.filter(f => !applied.has(f));

    if (pending.length === 0) {
      console.log('[AutoMigrate] No pending migrations');
      return 0;
    }

    console.log(`[AutoMigrate] Found ${pending.length} pending migrations`);

    // Run each pending migration in order
    for (const filename of pending) {
      await runMigration(pool, filename);
    }

    console.log(`[AutoMigrate] Successfully applied ${pending.length} migrations`);
    return pending.length;

  } catch (error: any) {
    console.error('[AutoMigrate] Migration failed:', error.message);
    // Don't crash the server - log and continue
    // The specific failing migration will have been rolled back
    return -1;
  }
}

/**
 * Check migration status without running anything
 */
export async function checkMigrationStatus(pool: Pool): Promise<{
  applied: string[];
  pending: string[];
}> {
  await ensureMigrationsTable(pool);

  const applied = await getAppliedMigrations(pool);
  const available = getMigrationFiles();

  return {
    applied: available.filter(f => applied.has(f)),
    pending: available.filter(f => !applied.has(f)),
  };
}