import os
import threading
import time
from contextlib import contextmanager
from typing import Generator

from sqlalchemy import create_engine, schema, text
from sqlalchemy.engine import Engine, URL
from sqlalchemy.exc import InterfaceError as SAInterfaceError
from sqlalchemy.exc import OperationalError as SAOperationalError
from sqlalchemy.orm import declarative_base, sessionmaker
from psycopg2 import OperationalError as PGOperationalError
from psycopg2 import InterfaceError as PGInterfaceError

Base = declarative_base()

_ENGINE: Engine | None = None
_ENGINE_LOCK = threading.Lock()


class _ConnectionProxy:
    def __init__(self, conn):
        self._conn = conn

    def __getattr__(self, name):
        return getattr(self._conn, name)

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc, tb):
        if exc_type is None:
            try:
                self._conn.commit()
            except Exception:
                self._conn.rollback()
                raise
        else:
            try:
                self._conn.rollback()
            except Exception:
                pass
        return False


def _db_config() -> dict[str, str | int]:
    url = os.getenv("DATABASE_URL")
    if url:
        return {"url": url}

    return {
        "host": os.getenv("DB_HOST") or os.getenv("PGHOST") or "localhost",
        "port": int(os.getenv("DB_PORT") or os.getenv("PGPORT") or "5432"),
        "dbname": os.getenv("DB_NAME") or os.getenv("PGDATABASE") or "trading_db",
        "user": os.getenv("DB_USER") or os.getenv("PGUSER") or "trader",
        "password": os.getenv("DB_PASSWORD") or os.getenv("PGPASSWORD") or "traderpass",
        "connect_timeout": int(os.getenv("DB_CONNECT_TIMEOUT", "5")),
        "schema": os.getenv("DB_SCHEMA") or os.getenv("PGSCHEMA") or "quant_app",
    }


def get_database_url(cfg: dict[str, str | int] | None = None) -> str:
    cfg = cfg or _db_config()
    if "url" in cfg:
        return str(cfg["url"])
    schema_name = cfg.get("schema")
    query = {"connect_timeout": str(cfg["connect_timeout"])}
    if schema_name:
        query["options"] = f"-csearch_path={schema_name},public"
    url = URL.create(
        "postgresql+psycopg2",
        username=str(cfg["user"]),
        password=str(cfg["password"]),
        host=str(cfg["host"]),
        port=int(cfg["port"]),
        database=str(cfg["dbname"]),
        query=query,
    )
    return url.render_as_string(hide_password=False)


def _create_engine() -> Engine:
    cfg = _db_config()
    pool_size = int(os.getenv("DB_POOL_SIZE", os.getenv("DB_POOL_MIN", "5")))
    max_overflow = int(os.getenv("DB_POOL_MAX", "10"))
    pool_timeout = int(os.getenv("DB_POOL_TIMEOUT", "30"))
    engine = create_engine(
        get_database_url(cfg),
        pool_size=pool_size,
        max_overflow=max_overflow,
        pool_timeout=pool_timeout,
        pool_pre_ping=True,
        future=True,
    )
    schema_name = cfg.get("schema")
    if schema_name:
        try:
            with engine.begin() as conn:
                conn.execute(schema.CreateSchema(schema_name, if_not_exists=True))
        except Exception:
            # Schema creation is best-effort; permissions might be limited in some environments.
            pass
    return engine


def get_engine() -> Engine:
    global _ENGINE
    if _ENGINE is None:
        with _ENGINE_LOCK:
            if _ENGINE is None:
                _ENGINE = _create_engine()
    return _ENGINE


SessionLocal = sessionmaker(
    autocommit=False,
    autoflush=False,
    expire_on_commit=False,
    bind=get_engine(),
)


def _get_connection():
    return get_engine().raw_connection()


def _put_connection(conn, close=False):
    try:
        conn.close()
    except Exception:
        if not close:
            raise


@contextmanager
def db_connection(retries: int | None = None, delay: float | None = None):
    attempts = retries if retries is not None else int(os.getenv("DB_RETRY_COUNT", "3"))
    backoff = delay if delay is not None else float(os.getenv("DB_RETRY_DELAY", "0.2"))
    last_error = None
    for attempt in range(attempts):
        conn = None
        try:
            conn = _get_connection()
            conn.autocommit = False
            yield _ConnectionProxy(conn)
            return
        except (SAOperationalError, SAInterfaceError, PGOperationalError, PGInterfaceError) as exc:
            last_error = exc
            if conn is not None:
                _put_connection(conn)
                conn = None
            time.sleep(backoff * (2 ** attempt))
            continue
        finally:
            if conn is not None:
                _put_connection(conn, close=conn.closed != 0)
    if last_error:
        raise last_error


def run_with_retry(operation, retries: int | None = None, delay: float | None = None):
    attempts = retries if retries is not None else int(os.getenv("DB_RETRY_COUNT", "3"))
    backoff = delay if delay is not None else float(os.getenv("DB_RETRY_DELAY", "0.2"))
    last_error = None
    for attempt in range(attempts):
        with db_connection(retries=1) as conn:
            try:
                with conn.cursor() as cur:
                    result = operation(cur, conn)
                conn.commit()
                return result
            except (SAOperationalError, SAInterfaceError, PGOperationalError, PGInterfaceError) as exc:
                conn.rollback()
                last_error = exc
                time.sleep(backoff * (2 ** attempt))
                continue
            except Exception:
                conn.rollback()
                raise
    if last_error:
        raise last_error


@contextmanager
def db_transaction():
    with db_connection() as conn:
        try:
            with conn.cursor() as cur:
                yield cur
            conn.commit()
        except Exception:
            conn.rollback()
            raise


def get_db() -> Generator:
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def health_check() -> bool:
    try:
        with get_engine().connect() as conn:
            conn.execute(text("SELECT 1"))
        return True
    except Exception:
        return False