"""Async checkpointer factory.

Provides an **async context manager** for long-running async servers that need
proper resource cleanup.

Supported backends: memory, sqlite, postgres.

Usage (e.g. FastAPI lifespan)::

    from deerflow.agents.checkpointer.async_provider import make_checkpointer

    async with make_checkpointer() as checkpointer:
        app.state.checkpointer = checkpointer  # InMemorySaver if not configured

For sync usage see :mod:`deerflow.agents.checkpointer.provider`.
"""

from __future__ import annotations

import contextlib
import logging
from collections.abc import AsyncIterator

from langgraph.types import Checkpointer

from deerflow.agents.checkpointer.provider import (
    POSTGRES_CONN_REQUIRED,
    POSTGRES_INSTALL,
    SQLITE_INSTALL,
    _resolve_sqlite_conn_str,
)
from deerflow.config.app_config import get_app_config

logger = logging.getLogger(__name__)

# ---------------------------------------------------------------------------
# Async factory
# ---------------------------------------------------------------------------


@contextlib.asynccontextmanager
async def _async_checkpointer(config) -> AsyncIterator[Checkpointer]:
    """Async context manager that constructs and tears down a checkpointer."""
    if config.type == "memory":
        from langgraph.checkpoint.memory import InMemorySaver

        yield InMemorySaver()
        return

    if config.type == "sqlite":
        try:
            from langgraph.checkpoint.sqlite.aio import AsyncSqliteSaver
        except ImportError as exc:
            raise ImportError(SQLITE_INSTALL) from exc

        import pathlib

        conn_str = _resolve_sqlite_conn_str(config.connection_string or "store.db")
        # Only create parent directories for real filesystem paths
        if conn_str != ":memory:" and not conn_str.startswith("file:"):
            pathlib.Path(conn_str).parent.mkdir(parents=True, exist_ok=True)
        async with AsyncSqliteSaver.from_conn_string(conn_str) as saver:
            await saver.setup()
            yield saver
        return

    if config.type == "postgres":
        try:
            from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
        except ImportError as exc:
            raise ImportError(POSTGRES_INSTALL) from exc

        if not config.connection_string:
            raise ValueError(POSTGRES_CONN_REQUIRED)

        async with AsyncPostgresSaver.from_conn_string(config.connection_string) as saver:
            await saver.setup()
            yield saver
        return

    raise ValueError(f"Unknown checkpointer type: {config.type!r}")


# ---------------------------------------------------------------------------
# Public async context manager
# ---------------------------------------------------------------------------


@contextlib.asynccontextmanager
async def make_checkpointer() -> AsyncIterator[Checkpointer]:
    """Async context manager that yields a checkpointer for the caller's lifetime.
    Resources are opened on enter and closed on exit — no global state::

        async with make_checkpointer() as checkpointer:
            app.state.checkpointer = checkpointer

    Yields an ``InMemorySaver`` when no checkpointer is configured in *config.yaml*.
    """

    config = get_app_config()

    if config.checkpointer is None:
        from langgraph.checkpoint.memory import InMemorySaver

        yield InMemorySaver()
        return

    async with _async_checkpointer(config.checkpointer) as saver:
        yield saver