"""Redis sessions owned by authenticated client Agent customers."""

from __future__ import annotations

import time
import uuid
from inspect import isawaitable

from agent.customer_agent.session import SessionOwnershipError


async def _config(config_getter, key: str, default):
    value = config_getter(key, str(default))
    if isawaitable(value):
        value = await value
    return type(default)(value)


class ClientSessionService:
    """Create and verify Redis sessions bound to a customer ID."""

    def __init__(self, redis, *, config_getter, clock=time.time):
        self.redis = redis
        self.config_getter = config_getter
        self.clock = clock

    async def create_session(self, customer_id: int) -> str:
        """Create a session whose Redis owner value is the current customer."""
        session_id = uuid.uuid4().hex
        ttl = await _config(self.config_getter, "agent.customer.session.ttl", 1800)
        await self.redis.set(f"session:{session_id}", str(customer_id), ex=ttl)
        await self.redis.rpush(f"session:{session_id}:messages", "")
        await self.redis.expire(f"session:{session_id}:messages", ttl)
        return session_id

    async def verify_session_ownership(self, session_id: str, *, customer_id: int) -> None:
        """Reject missing sessions and sessions owned by another customer."""
        owner = await self.redis.get(f"session:{session_id}")
        if owner is None:
            raise SessionOwnershipError(404, "会话不存在或已过期")
        if isinstance(owner, bytes):
            owner = owner.decode()
        if str(owner) != str(customer_id):
            raise SessionOwnershipError(403, "无权访问该会话")

    async def consume_chat_quota(self, session_id: str, *, customer_id: int) -> int | None:
        """Apply the existing per-session rate limit with a customer-scoped key."""
        window = await _config(
            self.config_getter, "agent.customer.rate_limit.window_sec", 60
        )
        maximum = await _config(
            self.config_getter, "agent.customer.rate_limit.max_requests", 20
        )
        key = f"rate:limit:client:{customer_id}:{session_id}:chat"
        now = self.clock()
        await self.redis.zremrangebyscore(key, 0, (now - window) * 1000)
        count = await self.redis.zcard(key)
        if count >= maximum:
            entries = getattr(self.redis, "sorted_sets", {}).get(key, [])
            oldest = min((score for score, _ in entries), default=now * 1000)
            return max(1, int((oldest / 1000 + window) - now))
        await self.redis.zadd(key, {uuid.uuid4().hex: now * 1000})
        await self.redis.expire(key, window)
        return None

__all__ = ["ClientSessionService", "SessionOwnershipError"]