from __future__ import annotations

import time
from collections import defaultdict, deque
from collections.abc import Hashable

from fastapi import HTTPException, Request, status
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.config import settings
from app.models.user import User

BucketKey = tuple[str, Hashable]

_buckets: dict[BucketKey, deque[float]] = defaultdict(deque)
_redis_client = None


def reset_rate_limit_state() -> None:
    _buckets.clear()


async def check_rate_limit(
    *,
    scope: str,
    limit: int,
    window_seconds: int,
    request: Request | None = None,
    user: User | None = None,
    session: AsyncSession | None = None,
) -> None:
    identifiers: list[Hashable] = []
    if user is not None:
        identifiers.append(f"user:{user.id}")
        identifiers.append(f"telegram:{user.telegram_id}")
    if request is not None and request.client is not None:
        identifiers.append(f"ip:{request.client.host}")
    if not identifiers:
        identifiers.append("anonymous")

    if settings.redis_url:
        allowed = await check_redis_rate_limit(scope, identifiers, limit, window_seconds)
        if not allowed:
            await log_rate_limit_event(
                session,
                scope=scope,
                identifier="redis",
                user=user,
                request=request,
            )
            raise_rate_limit(scope, window_seconds)
        return

    now = time.monotonic()
    for identifier in identifiers:
        key = (scope, identifier)
        bucket = _buckets[key]
        while bucket and now - bucket[0] > window_seconds:
            bucket.popleft()
        if len(bucket) >= limit:
            await log_rate_limit_event(
                session,
                scope=scope,
                identifier=str(identifier),
                user=user,
                request=request,
            )
            raise_rate_limit(scope, window_seconds)
    for identifier in identifiers:
        _buckets[(scope, identifier)].append(now)


def raise_rate_limit(scope: str, window_seconds: int) -> None:
    raise HTTPException(
        status_code=status.HTTP_429_TOO_MANY_REQUESTS,
        detail={
            "code": "rate_limit_exceeded",
            "message": "Слишком много запросов. Попробуйте чуть позже.",
            "scope": scope,
            "retry_after_seconds": window_seconds,
        },
    )


async def get_redis_client():
    global _redis_client
    if _redis_client is not None:
        return _redis_client
    try:
        from redis.asyncio import Redis
    except ImportError:
        return None
    _redis_client = Redis.from_url(settings.redis_url, encoding="utf-8", decode_responses=True)
    return _redis_client


async def check_redis_rate_limit(
    scope: str,
    identifiers: list[Hashable],
    limit: int,
    window_seconds: int,
) -> bool:
    client = await get_redis_client()
    if client is None:
        return True
    now_window = int(time.time() // window_seconds)
    keys = [f"rl:{scope}:{identifier}:{now_window}" for identifier in identifiers]
    pipe = client.pipeline()
    for key in keys:
        pipe.incr(key)
        pipe.expire(key, window_seconds * 2)
    results = await pipe.execute()
    counts = [int(results[index]) for index in range(0, len(results), 2)]
    return all(count <= limit for count in counts)


async def log_rate_limit_event(
    session: AsyncSession | None,
    *,
    scope: str,
    identifier: str,
    user: User | None = None,
    request: Request | None = None,
) -> None:
    client_host = request.client.host if request and request.client else None
    user_agent = request.headers.get("user-agent") if request else None
    metadata = {
        "scope": scope,
        "identifier": identifier,
        "telegram_id": user.telegram_id if user else None,
        "user_id": user.id if user else None,
        "ip": client_host,
    }

    if session is None:
        from app.db.session import async_session_factory

        async with async_session_factory() as event_session:
            await persist_rate_limit_event(
                event_session,
                scope=scope,
                identifier=identifier,
                user=user,
                client_host=client_host,
                user_agent=user_agent,
                metadata=metadata,
            )
        return

    await persist_rate_limit_event(
        session,
        scope=scope,
        identifier=identifier,
        user=user,
        client_host=client_host,
        user_agent=user_agent,
        metadata=metadata,
    )


async def persist_rate_limit_event(
    event_session: AsyncSession,
    *,
    scope: str,
    identifier: str,
    user: User | None,
    client_host: str | None,
    user_agent: str | None,
    metadata: dict,
) -> None:
    from app.models.car import AuditLog
    from app.services.admin_notifications import create_admin_notification

    try:
        event_session.add(
            AuditLog(
                actor_user_id=user.id if user else None,
                actor_role=user.platform_role if user else "system",
                action="rate_limit.exceeded",
                target_type=scope,
                target_id=identifier[:80],
                metadata_json=metadata,
                ip=client_host,
                user_agent=user_agent[:256] if user_agent else None,
            )
        )
        await create_admin_notification(
            event_session,
            event_type="rate_limit_exceeded",
            title="Rate limit exceeded",
            body=f"Scope: {scope}\nIdentifier: {identifier}",
            entity_type="user" if user else "system",
            entity_id=user.id if user else scope,
            severity="warning",
            idempotency_key=f"rate_limit:{scope}:{identifier}:{int(time.time() // max(60, 1))}",
            metadata=metadata,
        )
        await event_session.commit()
    except Exception:
        await event_session.rollback()