"""SQLAlchemy-powered Session backend.

Usage::

    from agents.extensions.memory import SQLAlchemySession

    # Create from SQLAlchemy URL (uses asyncpg driver under the hood for Postgres)
    session = SQLAlchemySession.from_url(
        session_id="user-123",
        url="postgresql+asyncpg://app:secret@db.example.com/agents",
        create_tables=True, # If you want to auto-create tables, set to True.
    )

    # Or pass an existing AsyncEngine that your application already manages
    session = SQLAlchemySession(
        session_id="user-123",
        engine=my_async_engine,
        create_tables=True, # If you want to auto-create tables, set to True.
    )

    await Runner.run(agent, "Hello", session=session)
"""

from __future__ import annotations

import asyncio
import json
import threading
from typing import Any, ClassVar

from sqlalchemy import (
    TIMESTAMP,
    Column,
    ForeignKey,
    Index,
    Integer,
    MetaData,
    String,
    Table,
    Text,
    delete,
    event,
    insert,
    select,
    text as sql_text,
    update,
)
from sqlalchemy.exc import IntegrityError, OperationalError
from sqlalchemy.ext.asyncio import AsyncEngine, async_sessionmaker, create_async_engine

from ...items import TResponseInputItem
from ...memory.session import SessionABC
from ...memory.session_settings import SessionSettings, resolve_session_limit


class SQLAlchemySession(SessionABC):
    """SQLAlchemy implementation of [`Session`][agents.memory.session.Session]."""

    _table_init_locks: ClassVar[dict[tuple[str, str, str], threading.Lock]] = {}
    _table_init_locks_guard: ClassVar[threading.Lock] = threading.Lock()
    _sqlite_configured_engines: ClassVar[set[int]] = set()
    _sqlite_configured_engines_guard: ClassVar[threading.Lock] = threading.Lock()
    _SQLITE_BUSY_TIMEOUT_MS: ClassVar[int] = 5000
    _SQLITE_LOCK_RETRY_DELAYS: ClassVar[tuple[float, ...]] = (0.05, 0.1, 0.2, 0.4, 0.8)
    _metadata: MetaData
    _sessions: Table
    _messages: Table
    session_settings: SessionSettings | None = None

    @classmethod
    def _get_table_init_lock(
        cls, engine: AsyncEngine, sessions_table: str, messages_table: str
    ) -> threading.Lock:
        lock_key = (
            engine.url.render_as_string(hide_password=True),
            sessions_table,
            messages_table,
        )
        with cls._table_init_locks_guard:
            lock = cls._table_init_locks.get(lock_key)
            if lock is None:
                lock = threading.Lock()
                cls._table_init_locks[lock_key] = lock
            return lock

    @classmethod
    def _configure_sqlite_engine(cls, engine: AsyncEngine) -> None:
        """Apply SQLite settings that reduce transient lock failures."""
        if engine.dialect.name != "sqlite":
            return

        engine_key = id(engine.sync_engine)
        with cls._sqlite_configured_engines_guard:
            if engine_key in cls._sqlite_configured_engines:
                return

            @event.listens_for(engine.sync_engine, "connect")
            def _configure_sqlite_connection(dbapi_connection: Any, _: Any) -> None:
                cursor = dbapi_connection.cursor()
                try:
                    cursor.execute(f"PRAGMA busy_timeout = {cls._SQLITE_BUSY_TIMEOUT_MS}")
                    cursor.execute("PRAGMA journal_mode = WAL")
                finally:
                    cursor.close()

            cls._sqlite_configured_engines.add(engine_key)

    @staticmethod
    def _is_sqlite_lock_error(exc: OperationalError) -> bool:
        return "database is locked" in str(exc).lower()

    async def _run_sqlite_write_with_retry(self, operation: Any) -> None:
        """Retry transient SQLite write lock failures with bounded backoff."""
        if self._engine.dialect.name != "sqlite":
            await operation()
            return

        for attempt, delay in enumerate((0.0, *self._SQLITE_LOCK_RETRY_DELAYS)):
            if delay:
                await asyncio.sleep(delay)
            try:
                await operation()
                return
            except OperationalError as exc:
                if not self._is_sqlite_lock_error(exc):
                    raise
                if attempt == len(self._SQLITE_LOCK_RETRY_DELAYS):
                    raise

    def __init__(
        self,
        session_id: str,
        *,
        engine: AsyncEngine,
        create_tables: bool = False,
        sessions_table: str = "agent_sessions",
        messages_table: str = "agent_messages",
        session_settings: SessionSettings | None = None,
    ):
        """Initializes a new SQLAlchemySession.

        Args:
            session_id (str): Unique identifier for the conversation.
            engine (AsyncEngine): A pre-configured SQLAlchemy async engine. The engine
                must be created with an async driver (e.g., 'postgresql+asyncpg://',
                'mysql+aiomysql://', or 'sqlite+aiosqlite://').
            create_tables (bool, optional): Whether to automatically create the required
                tables and indexes. Defaults to False for production use. Set to True for
                development and testing when migrations aren't used.
            sessions_table (str, optional): Override the default table name for sessions if needed.
            messages_table (str, optional): Override the default table name for messages if needed.
            session_settings (SessionSettings | None, optional): Session configuration settings
        """
        self.session_id = session_id
        self.session_settings = session_settings or SessionSettings()
        self._engine = engine
        self._configure_sqlite_engine(engine)
        self._init_lock = (
            self._get_table_init_lock(engine, sessions_table, messages_table)
            if create_tables
            else None
        )

        self._metadata = MetaData()
        self._sessions = Table(
            sessions_table,
            self._metadata,
            Column("session_id", String, primary_key=True),
            Column(
                "created_at",
                TIMESTAMP(timezone=False),
                server_default=sql_text("CURRENT_TIMESTAMP"),
                nullable=False,
            ),
            Column(
                "updated_at",
                TIMESTAMP(timezone=False),
                server_default=sql_text("CURRENT_TIMESTAMP"),
                onupdate=sql_text("CURRENT_TIMESTAMP"),
                nullable=False,
            ),
        )

        self._messages = Table(
            messages_table,
            self._metadata,
            Column("id", Integer, primary_key=True, autoincrement=True),
            Column(
                "session_id",
                String,
                ForeignKey(f"{sessions_table}.session_id", ondelete="CASCADE"),
                nullable=False,
            ),
            Column("message_data", Text, nullable=False),
            Column(
                "created_at",
                TIMESTAMP(timezone=False),
                server_default=sql_text("CURRENT_TIMESTAMP"),
                nullable=False,
            ),
            Index(
                f"idx_{messages_table}_session_time",
                "session_id",
                "created_at",
            ),
            sqlite_autoincrement=True,
        )

        # Async session factory
        self._session_factory = async_sessionmaker(self._engine, expire_on_commit=False)

        self._create_tables = create_tables

    # ---------------------------------------------------------------------
    # Convenience constructors
    # ---------------------------------------------------------------------
    @classmethod
    def from_url(
        cls,
        session_id: str,
        *,
        url: str,
        engine_kwargs: dict[str, Any] | None = None,
        session_settings: SessionSettings | None = None,
        **kwargs: Any,
    ) -> SQLAlchemySession:
        """Create a session from a database URL string.

        Args:
            session_id (str): Conversation ID.
            url (str): Any SQLAlchemy async URL, e.g. "postgresql+asyncpg://user:pass@host/db".
            engine_kwargs (dict[str, Any] | None): Additional keyword arguments forwarded to
                sqlalchemy.ext.asyncio.create_async_engine.
            session_settings (SessionSettings | None): Session configuration settings including
                default limit for retrieving items. If None, uses default SessionSettings().
            **kwargs: Additional keyword arguments forwarded to the main constructor
                (e.g., create_tables, custom table names, etc.).

        Returns:
            SQLAlchemySession: An instance of SQLAlchemySession connected to the specified database.
        """
        engine_kwargs = engine_kwargs or {}
        engine = create_async_engine(url, **engine_kwargs)
        return cls(session_id, engine=engine, session_settings=session_settings, **kwargs)

    async def _serialize_item(self, item: TResponseInputItem) -> str:
        """Serialize an item to JSON string. Can be overridden by subclasses."""
        return json.dumps(item, separators=(",", ":"))

    async def _deserialize_item(self, item: str) -> TResponseInputItem:
        """Deserialize a JSON string to an item. Can be overridden by subclasses."""
        return json.loads(item)  # type: ignore[no-any-return]

    # ------------------------------------------------------------------
    # Session protocol implementation
    # ------------------------------------------------------------------
    async def _ensure_tables(self) -> None:
        """Ensure tables are created before any database operations."""
        if not self._create_tables:
            return

        assert self._init_lock is not None
        while not self._init_lock.acquire(blocking=False):
            # Poll without handing lock acquisition to a background thread so
            # cancellation cannot strand the shared init lock in the acquired state.
            await asyncio.sleep(0.01)
        try:
            if not self._create_tables:
                return

            async with self._engine.begin() as conn:
                await conn.run_sync(self._metadata.create_all)
            self._create_tables = False  # Only create once
        finally:
            self._init_lock.release()

    async def get_items(self, limit: int | None = None) -> list[TResponseInputItem]:
        """Retrieve the conversation history for this session.

        Args:
            limit: Maximum number of items to retrieve. If None, uses session_settings.limit.
                   When specified, returns the latest N items in chronological order.

        Returns:
            List of input items representing the conversation history
        """
        await self._ensure_tables()

        session_limit = resolve_session_limit(limit, self.session_settings)

        async with self._session_factory() as sess:
            if session_limit is None:
                stmt = (
                    select(self._messages.c.message_data)
                    .where(self._messages.c.session_id == self.session_id)
                    .order_by(
                        self._messages.c.created_at.asc(),
                        self._messages.c.id.asc(),
                    )
                )
            else:
                stmt = (
                    select(self._messages.c.message_data)
                    .where(self._messages.c.session_id == self.session_id)
                    # Use DESC + LIMIT to get the latest N
                    # then reverse later for chronological order.
                    .order_by(
                        self._messages.c.created_at.desc(),
                        self._messages.c.id.desc(),
                    )
                    .limit(session_limit)
                )

            result = await sess.execute(stmt)
            rows: list[str] = [row[0] for row in result.all()]

            if session_limit is not None:
                rows.reverse()

            items: list[TResponseInputItem] = []
            for raw in rows:
                try:
                    items.append(await self._deserialize_item(raw))
                except json.JSONDecodeError:
                    # Skip corrupted rows
                    continue
            return items

    async def add_items(self, items: list[TResponseInputItem]) -> None:
        """Add new items to the conversation history.

        Args:
            items: List of input items to add to the history
        """
        if not items:
            return

        await self._ensure_tables()
        payload = [
            {
                "session_id": self.session_id,
                "message_data": await self._serialize_item(item),
            }
            for item in items
        ]

        async def _write_items() -> None:
            async with self._session_factory() as sess:
                async with sess.begin():
                    # Avoid check-then-insert races on the first write while keeping
                    # the common path free of avoidable integrity exceptions.
                    existing = await sess.execute(
                        select(self._sessions.c.session_id).where(
                            self._sessions.c.session_id == self.session_id
                        )
                    )
                    if not existing.scalar_one_or_none():
                        try:
                            async with sess.begin_nested():
                                await sess.execute(
                                    insert(self._sessions).values({"session_id": self.session_id})
                                )
                        except IntegrityError:
                            # Another concurrent writer created the parent row first.
                            pass

                    # Insert messages in bulk
                    await sess.execute(insert(self._messages), payload)

                    # Touch updated_at column
                    await sess.execute(
                        update(self._sessions)
                        .where(self._sessions.c.session_id == self.session_id)
                        .values(updated_at=sql_text("CURRENT_TIMESTAMP"))
                    )

        await self._run_sqlite_write_with_retry(_write_items)

    async def pop_item(self) -> TResponseInputItem | None:
        """Remove and return the most recent item from the session.

        Returns:
            The most recent item if it exists, None if the session is empty
        """
        await self._ensure_tables()
        async with self._session_factory() as sess:
            async with sess.begin():
                while True:
                    # Fallback for all dialects - get ID first, then delete
                    subq = (
                        select(self._messages.c.id)
                        .where(self._messages.c.session_id == self.session_id)
                        .order_by(
                            self._messages.c.created_at.desc(),
                            self._messages.c.id.desc(),
                        )
                        .limit(1)
                    )
                    res = await sess.execute(subq)
                    row_id = res.scalar_one_or_none()
                    if row_id is None:
                        return None
                    # Fetch data before deleting
                    res_data = await sess.execute(
                        select(self._messages.c.message_data).where(self._messages.c.id == row_id)
                    )
                    row = res_data.scalar_one_or_none()
                    await sess.execute(delete(self._messages).where(self._messages.c.id == row_id))

                    if row is None:
                        continue
                    try:
                        return await self._deserialize_item(row)
                    except (json.JSONDecodeError, TypeError):
                        continue

    async def clear_session(self) -> None:
        """Clear all items for this session."""
        await self._ensure_tables()
        async with self._session_factory() as sess:
            async with sess.begin():
                await sess.execute(
                    delete(self._messages).where(self._messages.c.session_id == self.session_id)
                )
                await sess.execute(
                    delete(self._sessions).where(self._sessions.c.session_id == self.session_id)
                )

    @property
    def engine(self) -> AsyncEngine:
        """Access the underlying SQLAlchemy AsyncEngine.

        This property provides direct access to the engine for advanced use cases,
        such as checking connection pool status, configuring engine settings,
        or manually disposing the engine when needed.

        Returns:
            AsyncEngine: The SQLAlchemy async engine instance.
        """
        return self._engine
