import psycopg2
import psycopg2.extras
import psycopg2.pool
from flask import g, current_app

# Module-level connection pool (initialised once per process)
_pool = None


def init_db(app):
    """Initialise the connection pool on startup."""
    global _pool
    try:
        _pool = psycopg2.pool.SimpleConnectionPool(
            minconn=2,
            maxconn=10,
            dsn=app.config["DATABASE_URL"],
        )
        print(" * Database connection pool OK (2–10 connections)")
    except Exception as e:
        print(f" * Database connection pool FAILED: {e}")


def get_db():
    """Get a pooled database connection for the current request."""
    if "db" not in g:
        g.db = _pool.getconn()
        g.db.cursor_factory = psycopg2.extras.RealDictCursor
    return g.db


def close_db(exception=None):
    """Return database connection to the pool at end of request."""
    db = g.pop("db", None)
    if db is not None:
        if exception:
            db.rollback()
        _pool.putconn(db)


def query(sql, params=None):
    """Execute a SELECT query and return all rows as dicts."""
    db = get_db()
    with db.cursor() as cur:
        cur.execute(sql, params)
        return cur.fetchall()


def query_one(sql, params=None):
    """Execute a SELECT query and return one row as a dict."""
    db = get_db()
    with db.cursor() as cur:
        cur.execute(sql, params)
        return cur.fetchone()


def execute(sql, params=None):
    """Execute an INSERT/UPDATE/DELETE and commit."""
    db = get_db()
    with db.cursor() as cur:
        cur.execute(sql, params)
        db.commit()


def execute_returning(sql, params=None):
    """Execute an INSERT/UPDATE/DELETE with RETURNING and commit."""
    db = get_db()
    with db.cursor() as cur:
        cur.execute(sql, params)
        row = cur.fetchone()
        db.commit()
        return row


def execute_many(sql, params_list):
    """Execute a batch INSERT/UPDATE/DELETE and commit."""
    db = get_db()
    with db.cursor() as cur:
        cur.executemany(sql, params_list)
        db.commit()