from mysql.connector import pooling, Error
from mysql.connector.pooling import MySQLConnectionPool, MySQLConnection
import threading
from secret_manager import return_credentials
import os
import time
from simple_logger_handler import setup_logger
from typing import Generator

db_username = return_credentials("/etc/secrets/db_username")
db_password = return_credentials("/etc/secrets/db_password")
db_host = os.getenv("BACKEND_API_DB_HOST","localhost")
db_database = os.getenv("BACKEND_API_DB_DATABASE","app")

logger = setup_logger(__name__)

MAX_RETRIES = 5
RETRY_DELAY = 5
HEALTHCHECK_INTERVAL = 60

MYSQL_CONFIG = {
	"host": db_host,
	"user": db_username,
	"password": db_password,
	"database": db_database,
	"connection_timeout": 10
}

_pool_lock = threading.Lock()
_connection_pool = None
_pool_name = "MySQLPool"
_health_thread = None
_stop_healthcheck = threading.Event()

def create_connection_pool(pool_name : str = None):
	"""
	Create a MySQL connection pool.

	Args:
		pool_name (str): Name for the connection pool overriding the default.

	Raises:
		RuntimeError: If pool creation fails after retries.
	"""
	global _connection_pool, _pool_name
	if pool_name:
		_pool_name = pool_name
	with _pool_lock:
		if _connection_pool is not None:
			logger.debug("[MySQL] Pool already exists, returning existing pool")
			return

	for attempt in range (1,MAX_RETRIES+1):
		try:
			logger.info(f"[MySQL] Attempt {attempt} to connect...")
			pool = pooling.MySQLConnectionPool(
				pool_name=_pool_name,
				pool_size=5,
				pool_reset_session=True,
				**MYSQL_CONFIG
			)
			with _pool_lock:
				_connection_pool = pool
			logger.info("[MySQL] Pool created", extra={"pool_name": pool.pool_name})
			return

		except Error as e:
			logger.warning(f"[MySQL] Attempt {attempt} failed: {e}")
			if attempt < MAX_RETRIES:
				logger.debug(f"[MySQL] Retrying in {RETRY_DELAY} seconds...")
				time.sleep(RETRY_DELAY)

	logger.critical(f"[MySQL] Failed to connect after {MAX_RETRIES} attempts.")
	raise RuntimeError("MySQL pool initialization failed")

def close_connection_pool():
	"""
	Close the MySQL connection pool and stop the healthcheck thread.
	"""
	global _connection_pool
	with _pool_lock:
		if _connection_pool:
			logger.debug(f"[MySQL] Closing pool: {_connection_pool}")
			_connection_pool = None
			logger.info("[MySQL] Connection pool closed")
	_stop_healthcheck.set()
	logger.debug("[MySQL] Healthcheck stop flag set")

def get_connection_pool() -> MySQLConnectionPool:
	"""
	Retrieve the existing MySQL connection pool, or create a new one if not initialized.

	Returns:
		MySQLConnectionPool: The active connection pool.
	"""
	global _connection_pool
	with _pool_lock:
		if _connection_pool is None:
			logger.debug("[MySQL] No pool found, creating one")
			create_connection_pool(_pool_name)
		else:
			logger.debug(f"[MySQL] Returning existing pool: {_connection_pool}")
	return _connection_pool

def get_db() -> Generator[MySQLConnection, None, None]:
	"""
	Context generator yielding a database connection from the pool.

	Yields:
		MySQLConnection: A live MySQL database connection.
	"""
	pool = get_connection_pool()
	logger.debug(f"[MySQL] Acquiring connection from pool: {pool}")
	conn = pool.get_connection()

	try:
		conn.ping(reconnect=True, attempts=3, delay=1)
		logger.debug("[MySQL] Connection alive")
	except Error as e:
		logger.warning(f"[MySQL] Connection dead, recreating pool: {e}")
		create_connection_pool(_pool_name)
		pool = get_connection_pool()
		conn = pool.get_connection()
		logger.debug("[MySQL] Reconnected successfully")

	try:
		yield conn
	finally:
		if conn and conn.is_connected():
			conn.close()
			logger.debug("[MySQL] Connection returned to pool")

def _pool_healthcheck():
	"""
	Internal function that periodically pings the database to ensure pool health.
	"""
	while not _stop_healthcheck.is_set():
		time.sleep(HEALTHCHECK_INTERVAL)
		with _pool_lock:
			pool = _connection_pool
		if not pool:
			logger.debug("[MySQL] Healthcheck skipped, pool not initialized")
			continue
		try:
			conn = pool.get_connection()
			conn.ping(reconnect=True, attempts=3, delay=1)
			conn.close()
			logger.debug(f"[MySQL] Pool healthcheck succeeded")
		except Error as e:
			logger.warning(f"[MySQL] Pool healthcheck failed: {e}")
			create_connection_pool()


def start_healthcheck_thread():
	"""
	Start the background thread that runs periodic pool healthchecks.
	"""
	global _health_thread
	if _health_thread and _health_thread.is_alive():
		logger.debug("[MySQL] Healthcheck thread already running")
		return
	_stop_healthcheck.clear()
	_health_thread = threading.Thread(target=_pool_healthcheck, daemon=True)
	_health_thread.start()
	logger.info("[MySQL] Healthcheck thread started.")