import hashlib
import hmac
import secrets
import threading
import time
from collections import defaultdict, deque
from datetime import datetime, timezone

from argon2 import PasswordHasher
from argon2.exceptions import InvalidHashError, VerificationError
from fastapi import Depends, HTTPException, Request, status
from psycopg import Connection

from .config import settings
from .db import get_connection

password_hasher = PasswordHasher()


def hash_password(password: str) -> str:
    return password_hasher.hash(password)


def verify_password(password: str, password_hash: str) -> bool:
    try:
        return password_hasher.verify(password_hash, password)
    except (InvalidHashError, VerificationError):
        return False


def token_digest(token: str) -> str:
    return hashlib.sha256(token.encode("utf-8")).hexdigest()


def new_token() -> str:
    return secrets.token_urlsafe(32)


def new_csrf_token() -> str:
    return secrets.token_urlsafe(32)


def code_digest(code: str) -> str:
    return hmac.new(settings.csrf_secret.encode(), code.encode(), hashlib.sha256).hexdigest()


def utc_now() -> datetime:
    return datetime.now(timezone.utc)


def check_origin(request: Request) -> None:
    origin = request.headers.get("origin")
    if origin and origin.rstrip("/") not in settings.allowed_origins:
        raise HTTPException(status_code=403, detail={"code": "ORIGIN_NOT_ALLOWED", "message": "请求来源不被允许"})


def require_csrf(request: Request) -> None:
    check_origin(request)
    header = request.headers.get("x-csrf-token")
    cookie = request.cookies.get("kaotings_csrf")
    if not header or not cookie or not hmac.compare_digest(header, cookie):
        raise HTTPException(status_code=403, detail={"code": "CSRF_FAILED", "message": "请求校验失败"})


def set_session_cookie(response, token: str) -> None:
    response.set_cookie(
        settings.session_cookie_name,
        token,
        max_age=settings.session_ttl_seconds,
        httponly=True,
        secure=settings.session_cookie_secure,
        samesite="lax",
        path="/",
    )


def clear_session_cookie(response) -> None:
    response.delete_cookie(settings.session_cookie_name, path="/")


def set_csrf_cookie(response, token: str) -> None:
    response.set_cookie("kaotings_csrf", token, max_age=settings.session_ttl_seconds, httponly=False, secure=settings.session_cookie_secure, samesite="lax", path="/")


def current_user(request: Request, connection: Connection = Depends(get_connection)) -> dict:
    token = request.cookies.get(settings.session_cookie_name)
    if not token:
        raise HTTPException(status_code=401, detail={"code": "AUTH_REQUIRED", "message": "请先登录"})
    user = connection.execute(
        """
        SELECT u.*, s.id AS session_id
        FROM sessions s JOIN users u ON u.id = s.user_id
        WHERE s.token_hash = %s AND s.revoked_at IS NULL AND s.expires_at > now()
        """,
        (token_digest(token),),
    ).fetchone()
    if not user:
        raise HTTPException(status_code=401, detail={"code": "AUTH_REQUIRED", "message": "会话已失效"})
    if user["status"] != "active":
        raise HTTPException(status_code=403, detail={"code": "ACCOUNT_DISABLED", "message": "账户不可用"})
    return user


def require_admin(user: dict = Depends(current_user)) -> dict:
    if user["role"] != "admin":
        raise HTTPException(status_code=403, detail={"code": "FORBIDDEN", "message": "无权执行此操作"})
    return user


class RateLimiter:
    def __init__(self) -> None:
        self._events: dict[str, deque[float]] = defaultdict(deque)
        self._lock = threading.Lock()

    def allow(self, key: str, limit: int, window_seconds: int) -> bool:
        now = time.monotonic()
        with self._lock:
            events = self._events[key]
            while events and events[0] <= now - window_seconds:
                events.popleft()
            if len(events) >= limit:
                return False
            events.append(now)
            return True


rate_limiter = RateLimiter()


_captcha_lock = threading.Lock()
_captchas: dict[str, dict[str, object]] = {}
_captcha_alphabet = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"


def new_captcha(client_key: str) -> tuple[str, str]:
    captcha_id = secrets.token_urlsafe(18)
    answer = "".join(secrets.choice(_captcha_alphabet) for _ in range(5))
    now = time.monotonic()
    with _captcha_lock:
        for key, item in list(_captchas.items()):
            if float(item["expires_at"]) <= now:
                _captchas.pop(key, None)
        _captchas[captcha_id] = {"answer": answer, "client_key": client_key, "expires_at": now + 300, "attempts": 0}
    return captcha_id, answer


def consume_captcha(captcha_id: str, answer: str, client_key: str) -> bool:
    with _captcha_lock:
        item = _captchas.get(captcha_id)
        if not item or float(item["expires_at"]) <= time.monotonic() or item["client_key"] != client_key:
            return False
        item["attempts"] = int(item["attempts"]) + 1
        valid = hmac.compare_digest(str(item["answer"]), answer.strip().upper())
        if valid or int(item["attempts"]) >= 5:
            _captchas.pop(captcha_id, None)
        return valid