import { EventEmitter } from 'events';
import fs from 'fs/promises';
import { PGlite } from '@electric-sql/pglite';
import { Pool } from 'pg';
import {
  createLookupHash,
  decryptBuffer,
  decryptJson,
  encryptBuffer,
  encryptJson,
  packEncryptedBuffer,
  unpackEncryptedBuffer,
} from './cryptoUtils.js';
import {
  hasEmbeddedPostgresDatabaseFiles,
  isPostgresStorageMode,
  POSTGRES_STORAGE_DB_DIR,
  POSTGRES_STORAGE_DIR,
  readPostgresStorageManifest,
  STORAGE_MODE,
} from './dataPaths.js';
import { APP_SCHEMA_NAME, POSTGRES_SCHEMA_SQL } from './postgresSchema.js';

let poolInstance = null;
let initPromise = null;
let activeBackendType = null;
const configuredClients = new WeakSet();
const patchedPools = new WeakSet();

function resolveSslConfig() {
  const raw = String(process.env.PGSSL || process.env.PGSSLMODE || '').trim().toLowerCase();
  if (!raw || ['false', '0', 'off', 'disable'].includes(raw)) return false;
  return { rejectUnauthorized: false };
}

function getValidatedSchemaName() {
  const schemaName = String(APP_SCHEMA_NAME || '').trim();
  if (!/^[A-Za-z_][A-Za-z0-9_]*$/.test(schemaName)) {
    throw new Error(`Invalid POSTGRES_APP_SCHEMA value: ${schemaName}`);
  }
  return schemaName;
}

export function getPostgresSchemaName() {
  return getValidatedSchemaName();
}

export function getCreateSchemaSql() {
  return `CREATE SCHEMA IF NOT EXISTS "${getValidatedSchemaName()}"`;
}

export function getDropSchemaSql() {
  return `DROP SCHEMA IF EXISTS "${getValidatedSchemaName()}" CASCADE`;
}

export function getSetSearchPathSql() {
  return `SET search_path TO "${getValidatedSchemaName()}", public`;
}

export function hasExternalPostgresConfig() {
  const connectionString = process.env.DATABASE_URL || process.env.POSTGRES_URL || '';
  if (connectionString) return true;
  const { PGHOST, PGUSER, PGDATABASE } = process.env;
  return !!(PGHOST && PGUSER && PGDATABASE);
}

function getRequestedBackendType() {
  const raw = String(process.env.POSTGRES_STORAGE_BACKEND || '').trim().toLowerCase();
  return raw === 'embedded' || raw === 'external' ? raw : null;
}

function getManifestBackendType() {
  const raw = String(readPostgresStorageManifest()?.backend || '').trim().toLowerCase();
  return raw === 'embedded' || raw === 'external' ? raw : null;
}

function resolveBackendType(explicit = null) {
  if (explicit === 'embedded' || explicit === 'external') return explicit;
  const requested = getRequestedBackendType();
  if (requested) return requested;
  const manifestBackend = getManifestBackendType();
  if (manifestBackend) return manifestBackend;
  if (hasEmbeddedPostgresDatabaseFiles()) return 'embedded';
  if (hasExternalPostgresConfig()) return 'external';
  return 'embedded';
}

function normalizeQueryResult(result = {}) {
  const rows = Array.isArray(result.rows) ? result.rows : [];
  const affectedRows = Number(result.affectedRows || 0);
  return {
    ...result,
    rows,
    fields: Array.isArray(result.fields) ? result.fields : [],
    rowCount: rows.length || affectedRows || 0,
  };
}

class EmbeddedPostgresClient {
  constructor(executor) {
    this.executor = executor;
    this.embedded = true;
  }

  async query(text, params = []) {
    return normalizeQueryResult(await this.executor.query(text, params));
  }

  async exec(text) {
    const results = await this.executor.exec(text);
    return Array.isArray(results) ? results.map(normalizeQueryResult) : [];
  }

  release() {}
}

class EmbeddedPostgresPool extends EventEmitter {
  constructor(db, dataDir) {
    super();
    this.db = db;
    this.dataDir = dataDir;
    this.embedded = true;
  }

  async connect() {
    return new EmbeddedPostgresClient(this.db);
  }

  async query(text, params = []) {
    return normalizeQueryResult(await this.db.query(text, params));
  }

  async exec(text) {
    const results = await this.db.exec(text);
    return Array.isArray(results) ? results.map(normalizeQueryResult) : [];
  }

  async transaction(fn) {
    return this.db.transaction(async (tx) => fn(new EmbeddedPostgresClient(tx)));
  }

  async end() {
    await this.db.close();
  }
}

function resolveEmbeddedDataDir(dataDir = null) {
  return dataDir || POSTGRES_STORAGE_DB_DIR;
}

function buildExternalPoolConfig() {
  const connectionString = process.env.DATABASE_URL || process.env.POSTGRES_URL || '';
  const ssl = resolveSslConfig();
  if (connectionString) {
    return { connectionString, ssl };
  }

  const { PGHOST, PGPORT, PGUSER, PGPASSWORD, PGDATABASE } = process.env;
  if (!PGHOST || !PGUSER || !PGDATABASE) {
    throw new Error(
      `PostgreSQL storage for ${POSTGRES_STORAGE_DIR} requires either an embedded database directory or a database connection. Set POSTGRES_STORAGE_BACKEND=embedded to use the local folder, or configure DATABASE_URL / PGHOST / PGUSER / PGDATABASE for an external server.`
    );
  }

  return {
    host: PGHOST,
    port: PGPORT ? Number(PGPORT) : 5432,
    user: PGUSER,
    password: PGPASSWORD || '',
    database: PGDATABASE,
    ssl,
  };
}

export function buildPoolConfig(options = {}) {
  const backend = resolveBackendType(options.backend);
  if (backend === 'embedded') {
    return {
      backend,
      dataDir: resolveEmbeddedDataDir(options.dataDir),
    };
  }
  return {
    backend,
    ...buildExternalPoolConfig(),
  };
}

function attachPoolErrorHandler(pool) {
  if (typeof pool.on === 'function') {
    pool.on('error', (err) => {
      console.error('PostgreSQL pool error:', err);
    });
  }
  return pool;
}

function patchPoolClientSetup(pool) {
  if (pool?.embedded || patchedPools.has(pool)) return pool;

  const originalConnect = pool.connect.bind(pool);
  const originalQuery = pool.query.bind(pool);

  // pool.query() bypasses our per-client setup, so wrap both entry points.
  pool.connect = async (...args) => {
    const client = await originalConnect(...args);
    await preparePostgresClient(client);
    return client;
  };

  pool.query = async (...args) => {
    if (typeof args[args.length - 1] === 'function') {
      return originalQuery(...args);
    }

    const client = await originalConnect();
    try {
      await preparePostgresClient(client);
      return await client.query(...args);
    } finally {
      client.release();
    }
  };

  patchedPools.add(pool);
  return pool;
}

async function createEmbeddedPostgresPool({ dataDir } = {}) {
  const resolvedDataDir = resolveEmbeddedDataDir(dataDir);
  await fs.mkdir(resolvedDataDir, { recursive: true });
  const db = await PGlite.create(resolvedDataDir);
  await db.query(getCreateSchemaSql());
  await db.query(getSetSearchPathSql());
  return attachPoolErrorHandler(new EmbeddedPostgresPool(db, resolvedDataDir));
}

export function getPostgresBackendType() {
  return activeBackendType || resolveBackendType();
}

export async function createRawPostgresPool(options = {}) {
  const config = buildPoolConfig(options);
  if (config.backend === 'embedded') {
    return createEmbeddedPostgresPool({ dataDir: config.dataDir });
  }
  const pool = new Pool(config);
  attachPoolErrorHandler(pool);
  return patchPoolClientSetup(pool);
}

export async function preparePostgresClient(client) {
  if (client?.embedded || configuredClients.has(client)) return;
  await client.query(getCreateSchemaSql());
  await client.query(getSetSearchPathSql());
  configuredClients.add(client);
}

export async function applyPostgresSchema(pool) {
  const client = await pool.connect();
  try {
    await preparePostgresClient(client);
    if (typeof client.exec === 'function') {
      await client.exec(POSTGRES_SCHEMA_SQL);
    } else {
      await client.query(POSTGRES_SCHEMA_SQL);
    }
  } finally {
    client.release();
  }
}

async function createPool() {
  return createStandalonePostgresPool();
}

export async function createStandalonePostgresPool(options = {}) {
  const pool = await createRawPostgresPool(options);
  await applyPostgresSchema(pool);
  activeBackendType = pool?.embedded ? 'embedded' : 'external';
  return pool;
}

export async function initializePostgresStorage() {
  if (!isPostgresStorageMode()) return false;
  if (!initPromise) {
    initPromise = createPool().then((pool) => {
      poolInstance = pool;
      activeBackendType = pool?.embedded ? 'embedded' : 'external';
      return pool;
    });
  }
  await initPromise;
  return true;
}

export async function getPostgresPool() {
  if (!isPostgresStorageMode()) {
    throw new Error(`PostgreSQL storage is not active (mode=${STORAGE_MODE})`);
  }
  await initializePostgresStorage();
  return poolInstance;
}

export async function pgQuery(text, params = []) {
  const pool = await getPostgresPool();
  return pool.query(text, params);
}

export async function withPgClient(fn) {
  const pool = await getPostgresPool();
  const client = await pool.connect();
  try {
    await preparePostgresClient(client);
    return await fn(client);
  } finally {
    client.release();
  }
}

export async function withPgTransaction(fn) {
  const pool = await getPostgresPool();
  if (typeof pool.transaction === 'function') {
    return pool.transaction(async (client) => {
      await preparePostgresClient(client);
      return fn(client);
    });
  }
  return withPgClient(async (client) => {
    await client.query('BEGIN');
    try {
      const result = await fn(client);
      await client.query('COMMIT');
      return result;
    } catch (err) {
      await client.query('ROLLBACK');
      throw err;
    }
  });
}

export function encryptJsonPayload(data, aad = '') {
  return encryptJson(data, aad);
}

export function decryptJsonPayload(payload, aad = '') {
  return decryptJson(payload, aad);
}

export function encryptBinaryPayload(buffer, aad = '') {
  return packEncryptedBuffer(encryptBuffer(Buffer.from(buffer), aad));
}

export function decryptBinaryPayload(payload, aad = '') {
  const packed = Buffer.isBuffer(payload) ? payload : Buffer.from(payload);
  return decryptBuffer(unpackEncryptedBuffer(packed), aad);
}

export function makeOwnerLookup(owner) {
  return createLookupHash(`${owner?.type || 'unknown'}:${owner?.id || ''}`, 'owner');
}

export function makeLookupToken(namespace, value) {
  return createLookupHash(String(value ?? ''), namespace);
}