from __future__ import annotations

from collections.abc import Generator, Mapping
import os
from typing import Any

from sqlalchemy import create_engine
from sqlalchemy.engine import Engine
from sqlalchemy.orm import Session, sessionmaker

from govoplan_core.db.query_metrics import instrument_engine


_POOL_SETTING_BOUNDS: dict[str, tuple[int, int]] = {
    "GOVOPLAN_DB_POOL_SIZE": (1, 100),
    "GOVOPLAN_DB_MAX_OVERFLOW": (0, 200),
    "GOVOPLAN_DB_POOL_TIMEOUT_SECONDS": (1, 300),
    "GOVOPLAN_DB_POOL_RECYCLE_SECONDS": (0, 86_400),
}


def default_connect_args(database_url: str) -> dict[str, Any]:
    return {"check_same_thread": False} if database_url.startswith("sqlite") else {}


def create_database_engine(
    database_url: str,
    *,
    pool_pre_ping: bool = True,
    connect_args: Mapping[str, Any] | None = None,
    **kwargs: Any,
) -> Engine:
    merged_connect_args = dict(default_connect_args(database_url))
    if connect_args:
        merged_connect_args.update(connect_args)
    if not database_url.startswith("sqlite"):
        kwargs.setdefault(
            "pool_size",
            _pool_setting("GOVOPLAN_DB_POOL_SIZE", 5),
        )
        kwargs.setdefault(
            "max_overflow",
            _pool_setting("GOVOPLAN_DB_MAX_OVERFLOW", 10),
        )
        kwargs.setdefault(
            "pool_timeout",
            _pool_setting("GOVOPLAN_DB_POOL_TIMEOUT_SECONDS", 30),
        )
        kwargs.setdefault(
            "pool_recycle",
            _pool_setting("GOVOPLAN_DB_POOL_RECYCLE_SECONDS", 1800),
        )
    return instrument_engine(create_engine(database_url, pool_pre_ping=pool_pre_ping, connect_args=merged_connect_args, **kwargs))


def _pool_setting(name: str, default: int) -> int:
    raw = os.environ.get(name)
    if raw is None:
        return default
    try:
        value = int(raw)
    except ValueError as exc:
        raise ValueError(f"{name} must be an integer") from exc
    minimum, maximum = _POOL_SETTING_BOUNDS[name]
    if not minimum <= value <= maximum:
        raise ValueError(
            f"{name} must be between {minimum} and {maximum}",
        )
    return value


class DatabaseHandle:
    def __init__(self, database_url: str, *, engine: Engine | None = None) -> None:
        self.database_url = database_url
        self.engine = instrument_engine(engine) if engine is not None else create_database_engine(database_url)
        self.SessionLocal = sessionmaker(bind=self.engine, autoflush=False, autocommit=False, expire_on_commit=False)

    def session(self) -> Session:
        return self.SessionLocal()

    def dependency(self) -> Generator[Session, None, None]:
        with self.SessionLocal() as session:
            yield session

    def dispose(self) -> None:
        self.engine.dispose()


_default_database: DatabaseHandle | None = None


def configure_database(database_url: str, *, engine: Engine | None = None, dispose_previous: bool = False) -> DatabaseHandle:
    global _default_database
    if engine is None and _default_database is not None and _default_database.database_url == database_url:
        return _default_database
    previous_database = _default_database
    _default_database = DatabaseHandle(database_url, engine=engine)
    if dispose_previous and previous_database is not None and previous_database is not _default_database:
        previous_database.dispose()
    return _default_database


def set_database(handle: DatabaseHandle) -> DatabaseHandle:
    global _default_database
    _default_database = handle
    return handle


def reset_database(*, dispose: bool = False) -> None:
    global _default_database
    if dispose and _default_database is not None:
        _default_database.dispose()
    _default_database = None


def get_database() -> DatabaseHandle:
    if _default_database is None:
        raise RuntimeError("GovOPlaN database is not configured")
    return _default_database


def get_session() -> Generator[Session, None, None]:
    yield from get_database().dependency()