"""EventStore implementation backed by AsyncKeyValue.

This module provides an EventStore implementation that enables SSE polling/resumability
for Streamable HTTP transports. Events are stored using the key_value package's
AsyncKeyValue protocol, allowing users to configure any compatible backend
(in-memory, Redis, etc.) following the same pattern as ResponseCachingMiddleware.
"""

from __future__ import annotations

from uuid import uuid4

from key_value.aio.adapters.pydantic import PydanticAdapter
from key_value.aio.protocols import AsyncKeyValue
from key_value.aio.stores.memory import MemoryStore
from mcp.server.streamable_http import EventCallback, EventId, EventMessage, StreamId
from mcp.server.streamable_http import EventStore as SDKEventStore
from mcp.types import JSONRPCMessage

from fastmcp.utilities.logging import get_logger
from fastmcp.utilities.types import FastMCPBaseModel

logger = get_logger(__name__)


class EventEntry(FastMCPBaseModel):
    """Stored event entry."""

    event_id: str
    stream_id: str
    message: dict | None  # JSONRPCMessage serialized to dict


class StreamEventList(FastMCPBaseModel):
    """List of event IDs for a stream."""

    event_ids: list[str]


class SessionScopedEventStore(SDKEventStore):
    """EventStore adapter that isolates stream IDs to one transport session."""

    def __init__(self, event_store: SDKEventStore, session_id: str):
        self._event_store = event_store
        self._stream_prefix = f"{len(session_id)}:{session_id}:"

    def _scope_stream_id(self, stream_id: StreamId) -> StreamId:
        return f"{self._stream_prefix}{stream_id}"

    def _unscope_stream_id(self, stream_id: StreamId) -> StreamId | None:
        if not stream_id.startswith(self._stream_prefix):
            return None
        return stream_id[len(self._stream_prefix) :]

    async def store_event(
        self, stream_id: StreamId, message: JSONRPCMessage | None
    ) -> EventId:
        return await self._event_store.store_event(
            self._scope_stream_id(stream_id), message
        )

    async def replay_events_after(
        self,
        last_event_id: EventId,
        send_callback: EventCallback,
    ) -> StreamId | None:
        replayed_events: list[EventMessage] = []

        async def buffer_event(event: EventMessage) -> None:
            replayed_events.append(event)

        scoped_stream_id = await self._event_store.replay_events_after(
            last_event_id, buffer_event
        )
        if scoped_stream_id is None:
            return None

        stream_id = self._unscope_stream_id(scoped_stream_id)
        if stream_id is None:
            logger.warning(
                "Event ID %s does not belong to this session-scoped event store",
                last_event_id,
            )
            return None

        for event in replayed_events:
            await send_callback(event)

        return stream_id


class EventStore(SDKEventStore):
    """EventStore implementation backed by AsyncKeyValue.

    Enables SSE polling/resumability by storing events that can be replayed
    when clients reconnect. Works with any AsyncKeyValue backend (memory, Redis, etc.)
    following the same pattern as ResponseCachingMiddleware and OAuthProxy.

    Example:
        ```python
        from fastmcp import FastMCP
        from fastmcp.server.event_store import EventStore

        # Default in-memory storage
        event_store = EventStore()

        # Or with a custom backend
        from key_value.aio.stores.redis import RedisStore
        redis_backend = RedisStore(url="redis://localhost")
        event_store = EventStore(storage=redis_backend)

        mcp = FastMCP("MyServer")
        app = mcp.http_app(event_store=event_store, retry_interval=2000)
        ```

    Args:
        storage: AsyncKeyValue backend. Defaults to MemoryStore.
        max_events_per_stream: Maximum events to retain per stream. Default 100.
        ttl: Event TTL in seconds. Default 3600 (1 hour). Set to None for no expiration.
    """

    def __init__(
        self,
        storage: AsyncKeyValue | None = None,
        max_events_per_stream: int = 100,
        ttl: int | None = 3600,
    ):
        self._storage: AsyncKeyValue = storage or MemoryStore()
        self._max_events_per_stream = max_events_per_stream
        self._ttl = ttl

        # PydanticAdapter for type-safe storage (following OAuth proxy pattern)
        self._event_store: PydanticAdapter[EventEntry] = PydanticAdapter[EventEntry](
            key_value=self._storage,
            pydantic_model=EventEntry,
            default_collection="fastmcp_events",
        )
        self._stream_store: PydanticAdapter[StreamEventList] = PydanticAdapter[
            StreamEventList
        ](
            key_value=self._storage,
            pydantic_model=StreamEventList,
            default_collection="fastmcp_streams",
        )

    async def store_event(
        self, stream_id: StreamId, message: JSONRPCMessage | None
    ) -> EventId:
        """Store an event and return its ID.

        Args:
            stream_id: ID of the stream the event belongs to
            message: The JSON-RPC message to store, or None for priming events

        Returns:
            The generated event ID for the stored event
        """
        event_id = str(uuid4())

        # Store the event entry
        entry = EventEntry(
            event_id=event_id,
            stream_id=stream_id,
            message=message.model_dump(mode="json") if message else None,
        )
        await self._event_store.put(key=event_id, value=entry, ttl=self._ttl)

        # Update stream's event list
        stream_data = await self._stream_store.get(key=stream_id)
        event_ids = stream_data.event_ids if stream_data else []
        event_ids.append(event_id)

        # Trim to max events (delete old events)
        if len(event_ids) > self._max_events_per_stream:
            for old_id in event_ids[: -self._max_events_per_stream]:
                await self._event_store.delete(key=old_id)
            event_ids = event_ids[-self._max_events_per_stream :]

        await self._stream_store.put(
            key=stream_id,
            value=StreamEventList(event_ids=event_ids),
            ttl=self._ttl,
        )

        return event_id

    async def replay_events_after(
        self,
        last_event_id: EventId,
        send_callback: EventCallback,
    ) -> StreamId | None:
        """Replay events that occurred after the specified event ID.

        Args:
            last_event_id: The ID of the last event the client received
            send_callback: A callback function to send events to the client

        Returns:
            The stream ID of the replayed events, or None if the event ID was not found
        """
        # Look up the event to find its stream
        entry = await self._event_store.get(key=last_event_id)
        if not entry:
            logger.warning(f"Event ID {last_event_id} not found in store")
            return None

        stream_id = entry.stream_id
        stream_data = await self._stream_store.get(key=stream_id)
        if not stream_data:
            logger.warning(f"Stream {stream_id} not found in store")
            return None

        event_ids = stream_data.event_ids

        # Find events after last_event_id
        try:
            start_idx = event_ids.index(last_event_id) + 1
        except ValueError:
            logger.warning(f"Event ID {last_event_id} not found in stream {stream_id}")
            return None

        # Replay events after the last one
        for event_id in event_ids[start_idx:]:
            event = await self._event_store.get(key=event_id)
            if event and event.message:
                msg = JSONRPCMessage.model_validate(event.message)
                await send_callback(EventMessage(msg, event.event_id))

        return stream_id
