"""Redis connection utilities for Mantimon TCG.

This module provides async Redis connection management with:
- Connection pooling
- JSON serialization helpers
- Proper cleanup on shutdown

Usage:
    from app.db.redis import get_redis, init_redis, close_redis

    # Initialize on startup
    await init_redis()

    # Use Redis
    async with get_redis() as redis:
        await redis.set("key", "value")
        value = await redis.get("key")

    # Close on shutdown
    await close_redis()

Key Patterns:
    - game:{game_id} - Active game state (JSON)
    - session:{session_id} - User session data
    - matchmaking:queue - Matchmaking queue
"""

import json
from collections.abc import AsyncGenerator
from contextlib import asynccontextmanager
from typing import Any

from redis.asyncio import ConnectionPool, Redis

from app.config import settings

# Global Redis pool (initialized by init_redis)
_pool: ConnectionPool | None = None


async def init_redis() -> ConnectionPool:
    """Initialize the Redis connection pool.

    Creates a connection pool configured based on application settings.
    Should be called once during application startup.

    Returns:
        The initialized ConnectionPool instance.

    Example:
        @app.on_event("startup")
        async def startup():
            await init_redis()
    """
    global _pool

    if _pool is not None:
        return _pool

    _pool = ConnectionPool.from_url(
        str(settings.redis_url),
        max_connections=settings.redis_max_connections,
        decode_responses=True,  # Return strings instead of bytes
    )

    return _pool


async def close_redis() -> None:
    """Close Redis connections and dispose of the pool.

    Should be called during application shutdown.

    Example:
        @app.on_event("shutdown")
        async def shutdown():
            await close_redis()
    """
    global _pool

    if _pool is not None:
        await _pool.disconnect()
        _pool = None


def get_pool() -> ConnectionPool:
    """Get the Redis connection pool.

    Returns:
        The initialized ConnectionPool instance.

    Raises:
        RuntimeError: If init_redis() has not been called.
    """
    if _pool is None:
        raise RuntimeError("Redis pool not initialized. Call init_redis() first.")
    return _pool


@asynccontextmanager
async def get_redis() -> AsyncGenerator[Redis, None]:
    """Get a Redis client from the connection pool.

    Provides a Redis client as an async context manager that
    automatically returns the connection to the pool.

    Yields:
        A Redis client instance.

    Raises:
        RuntimeError: If init_redis() has not been called.

    Example:
        async with get_redis() as redis:
            await redis.set("key", "value")
            value = await redis.get("key")
    """
    pool = get_pool()
    client = Redis(connection_pool=pool)
    try:
        yield client
    finally:
        await client.aclose()


class RedisHelper:
    """Helper class for common Redis operations with JSON support.

    Provides convenience methods for storing and retrieving JSON data,
    with proper serialization and error handling.

    Example:
        helper = RedisHelper()

        # Store JSON
        await helper.set_json("game:123", {"state": "active"})

        # Retrieve JSON
        data = await helper.get_json("game:123")

        # Delete
        await helper.delete("game:123")
    """

    async def get_json(self, key: str) -> dict[str, Any] | None:
        """Get and deserialize a JSON value from Redis.

        Args:
            key: Redis key to retrieve.

        Returns:
            Deserialized JSON data, or None if key doesn't exist.
        """
        async with get_redis() as client:
            value = await client.get(key)
            if value is None:
                return None
            return json.loads(value)

    async def set_json(
        self,
        key: str,
        value: dict[str, Any],
        expire_seconds: int | None = None,
    ) -> None:
        """Serialize and store a JSON value in Redis.

        Args:
            key: Redis key to store.
            value: Dictionary to serialize and store.
            expire_seconds: Optional TTL in seconds.
        """
        async with get_redis() as client:
            json_str = json.dumps(value, default=str)
            if expire_seconds:
                await client.setex(key, expire_seconds, json_str)
            else:
                await client.set(key, json_str)

    async def delete(self, key: str) -> bool:
        """Delete a key from Redis.

        Args:
            key: Redis key to delete.

        Returns:
            True if the key was deleted, False if it didn't exist.
        """
        async with get_redis() as client:
            result = await client.delete(key)
            return result > 0

    async def exists(self, key: str) -> bool:
        """Check if a key exists in Redis.

        Args:
            key: Redis key to check.

        Returns:
            True if the key exists, False otherwise.
        """
        async with get_redis() as client:
            result = await client.exists(key)
            return result > 0

    async def get_keys(self, pattern: str) -> list[str]:
        """Get all keys matching a pattern.

        Args:
            pattern: Redis key pattern (e.g., "game:*").

        Returns:
            List of matching keys.

        Note:
            Use sparingly in production as KEYS can be slow
            on large datasets. Consider SCAN for production use.
        """
        async with get_redis() as client:
            keys = await client.keys(pattern)
            return list(keys)

    async def set_with_ttl(
        self,
        key: str,
        value: str,
        ttl_seconds: int,
    ) -> None:
        """Set a string value with TTL.

        Args:
            key: Redis key to store.
            value: String value to store.
            ttl_seconds: Time-to-live in seconds.
        """
        async with get_redis() as client:
            await client.setex(key, ttl_seconds, value)

    async def increment(self, key: str, amount: int = 1) -> int:
        """Increment a counter.

        Args:
            key: Redis key for the counter.
            amount: Amount to increment by (default 1).

        Returns:
            The new counter value.
        """
        async with get_redis() as client:
            return await client.incrby(key, amount)


# Global helper instance
redis_helper = RedisHelper()