# crudkit/integrations/flask.py
from __future__ import annotations
from flask import Flask
from sqlalchemy.orm import scoped_session, sessionmaker
from ..engines import CRUDKitRuntime
from ..config import Config

def init_app(app: Flask, *, runtime: CRUDKitRuntime | None = None, config: type[Config] | None = None):
    """
    Initializes CRUDKit for a Flask app. Provides `app.extensions['crudkit']`
    with a runtime (engine + session_factory). Caller manages session lifecycle.
    """
    runtime = runtime or CRUDKitRuntime(config=config)
    app.extensions.setdefault("crudkit", {})
    app.extensions["crudkit"]["runtime"] = runtime

    # Build ONE sessionmaker bound to the ONE true engine object
    # so engine id == sessionmaker.bind id, always.
    engine = runtime.engine
    SessionFactory = runtime.session_factory or sessionmaker(bind=engine, **runtime._config.session_kwargs())
    app.extensions["crudkit"]["SessionFactory"] = SessionFactory
    app.extensions["crudkit"]["Session"] = scoped_session(SessionFactory)

    # Attach pool listeners to the *same* engine the SessionFactory is bound to.
    # Don’t guess. Don’t hope. Inspect.
    try:
        bound_engine = getattr(SessionFactory, "bind", None) or getattr(SessionFactory, "kw", {}).get("bind") or engine
        pool = bound_engine.pool

        from sqlalchemy import event

        @event.listens_for(pool, "checkout")
        def _on_checkout(dbapi_conn, conn_record, conn_proxy):
            sz = pool.size()
            chk = pool.checkedout()
            try:
                conns_in_pool = pool.checkedin()
            except Exception:
                conns_in_pool = "?"
            print(f"POOL CHECKOUT: Pool size: {sz}  Connections in pool: {conns_in_pool} "
                  f"Current Overflow: {pool.overflow()} Current Checked out connections: {chk} "
                  f"engine id= {id(bound_engine)}")

        @event.listens_for(pool, "checkin")
        def _on_checkin(dbapi_conn, conn_record):
            sz = pool.size()
            chk = pool.checkedout()
            try:
                conns_in_pool = pool.checkedin()
            except Exception:
                conns_in_pool = "?"
            print(f"POOL CHECKIN: Pool size: {sz}  Connections in pool: {conns_in_pool} "
                  f"Current Overflow: {pool.overflow()} Current Checked out connections: {chk} "
                  f"engine id= {id(bound_engine)}")
    except Exception as e:
        print(f"[crudkit.init_app] Failed to attach pool listeners: {e}")

    return runtime