/**
 * AlloyDB PostgreSQL client for vector semantic memory
 * 
 * Uses pgvector extension for semantic search over knowledge_chunks.
 * Connection pooling ensures efficient resource usage in Next.js API routes.
 */

import { Pool, PoolClient, QueryResult, QueryResultRow } from 'pg';
import { GoogleAuth } from 'google-auth-library';

let pool: Pool | null = null;
let cachedToken: { token: string; expiresAt: number } | null = null;

interface AlloyDBConfig {
  host: string;
  port: number;
  user: string;
  password: string;
  database: string;
  ssl?: boolean;
  maxConnections?: number;
  idleTimeoutMillis?: number;
}

/**
 * Get an OAuth2 access token for IAM authentication
 */
async function getAccessToken(): Promise<string> {
  // Check if we have a cached token that's still valid (with 5 min buffer)
  if (cachedToken && cachedToken.expiresAt > Date.now() + 5 * 60 * 1000) {
    return cachedToken.token;
  }

  const auth = new GoogleAuth({
    scopes: ['https://www.googleapis.com/auth/cloud-platform'],
  });

  const client = await auth.getClient();
  const tokenResponse = await client.getAccessToken();

  if (!tokenResponse.token) {
    throw new Error('Failed to get access token for AlloyDB IAM authentication');
  }

  // Cache the token (Google tokens typically expire in 1 hour)
  cachedToken = {
    token: tokenResponse.token,
    expiresAt: Date.now() + 55 * 60 * 1000, // 55 minutes (safe buffer)
  };

  return tokenResponse.token;
}

/**
 * Load AlloyDB configuration from environment variables
 */
async function loadConfig(): Promise<AlloyDBConfig> {
  const host = process.env.ALLOYDB_HOST;
  const port = process.env.ALLOYDB_PORT;
  const user = process.env.ALLOYDB_USER;
  const password = process.env.ALLOYDB_PASSWORD;
  const database = process.env.ALLOYDB_DATABASE;

  if (!host || !port || !user || !database) {
    throw new Error(
      'Missing required AlloyDB environment variables. Required: ALLOYDB_HOST, ALLOYDB_PORT, ALLOYDB_USER, ALLOYDB_DATABASE'
    );
  }

  // When using AlloyDB Auth Proxy, no password is needed (proxy handles IAM)
  // For direct connections with IAM, generate an OAuth token
  let finalPassword = password;
  if (!finalPassword && !host.startsWith('/')) {
    // Only generate token for direct IP connections, not Unix sockets
    finalPassword = await getAccessToken();
  }

  return {
    host,
    port: parseInt(port, 10),
    user,
    password: finalPassword || '', // Empty string for proxy connections
    database,
    ssl: process.env.ALLOYDB_SSL ? process.env.ALLOYDB_SSL !== 'false' : false, // Enable SSL if set to anything other than 'false'
    maxConnections: process.env.ALLOYDB_MAX_CONNECTIONS 
      ? parseInt(process.env.ALLOYDB_MAX_CONNECTIONS, 10) 
      : 10,
    idleTimeoutMillis: 30000, // 30 seconds
  };
}

/**
 * Initialize the connection pool (singleton pattern)
 */
async function initializePool(): Promise<Pool> {
  if (pool) {
    return pool;
  }

  const config = await loadConfig();

  pool = new Pool({
    host: config.host,
    port: config.port,
    user: config.user,
    password: config.password,
    database: config.database,
    ssl: config.ssl ? { rejectUnauthorized: false } : false,
    max: config.maxConnections,
    idleTimeoutMillis: config.idleTimeoutMillis,
    connectionTimeoutMillis: 10000, // 10 seconds to establish connection
  });

  // Log pool errors
  pool.on('error', (err) => {
    console.error('[AlloyDB Pool] Unexpected error on idle client:', err);
  });

  console.log(`[AlloyDB] Connection pool initialized (max: ${config.maxConnections})`);

  return pool;
}

/**
 * Get a pooled client for AlloyDB
 * 
 * This is the primary interface for accessing AlloyDB from Next.js API routes.
 * The pool handles connection reuse automatically.
 * 
 * @returns Pool instance for executing queries
 * 
 * @example
 * ```typescript
 * const pool = await getAlloyDbClient();
 * const result = await pool.query('SELECT * FROM knowledge_chunks WHERE project_id = $1', [projectId]);
 * ```
 */
export async function getAlloyDbClient(): Promise<Pool> {
  if (!pool) {
    return await initializePool();
  }
  return pool;
}

/**
 * Execute a query with automatic error logging
 * 
 * @param text SQL query text (use $1, $2, etc. for parameters)
 * @param params Query parameters
 * @returns Query result
 */
export async function executeQuery<T extends QueryResultRow = any>(
  text: string,
  params?: any[]
): Promise<QueryResult<T>> {
  const client = await getAlloyDbClient();
  try {
    const result = await client.query<T>(text, params);
    return result;
  } catch (error) {
    console.error('[AlloyDB Query Error]', {
      query: text,
      params,
      error: error instanceof Error ? error.message : String(error),
    });
    throw error;
  }
}

/**
 * Get a dedicated client from the pool for transactions
 * 
 * Remember to call client.release() when done!
 * 
 * @example
 * ```typescript
 * const client = await getPooledClient();
 * try {
 *   await client.query('BEGIN');
 *   await client.query('INSERT INTO ...');
 *   await client.query('COMMIT');
 * } catch (e) {
 *   await client.query('ROLLBACK');
 *   throw e;
 * } finally {
 *   client.release();
 * }
 * ```
 */
export async function getPooledClient(): Promise<PoolClient> {
  const pool = await getAlloyDbClient();
  return await pool.connect();
}

/**
 * Close the connection pool gracefully
 * 
 * Should be called during application shutdown (e.g., in tests or cleanup)
 */
export async function closeAlloyDbPool(): Promise<void> {
  if (pool) {
    await pool.end();
    pool = null;
    console.log('[AlloyDB] Connection pool closed');
  }
}

/**
 * Health check - verify AlloyDB connection is working
 */
export async function checkAlloyDbHealth(): Promise<boolean> {
  try {
    const result = await executeQuery('SELECT 1 as health_check');
    return result.rows.length > 0 && result.rows[0].health_check === 1;
  } catch (error) {
    console.error('[AlloyDB Health Check] Failed:', error);
    return false;
  }
}