"""密码哈希与 JWT。密钥优先用环境变量，否则写入 app_settings，重启后仍然有效。"""

from __future__ import annotations

import hashlib
import hmac
import secrets
from base64 import urlsafe_b64decode, urlsafe_b64encode
from datetime import timedelta

import jwt
from sqlalchemy.orm import Session

from app.clock import utcnow
from app.config import settings
from app.errors import AppError
from app.models import AppSetting, User

_secret: str | None = None
_ITERATIONS = 200_000


def hash_password(password: str) -> str:
    salt = secrets.token_bytes(16)
    digest = hashlib.pbkdf2_hmac("sha256", password.encode(), salt, _ITERATIONS)
    return f"pbkdf2_sha256${_ITERATIONS}${_b64(salt)}${_b64(digest)}"


def verify_password(password: str, stored: str | None) -> bool:
    if not stored:
        return False
    try:
        algo, rounds, salt_b64, digest_b64 = stored.split("$", 3)
        if algo != "pbkdf2_sha256":
            return False
        got = hashlib.pbkdf2_hmac("sha256", password.encode(), _unb64(salt_b64), int(rounds))
        return hmac.compare_digest(got, _unb64(digest_b64))
    except (ValueError, TypeError):
        return False


def ensure_jwt_secret(session: Session) -> None:
    global _secret
    if settings.jwt_secret:
        _secret = settings.jwt_secret
        return
    row = session.get(AppSetting, "jwt_secret")
    if row is None:
        row = AppSetting(key="jwt_secret", value=secrets.token_hex(32))
        session.add(row)
        session.flush()
    _secret = row.value


def create_access_token(user: User) -> str:
    payload = {
        "sub": str(user.id),
        "role": user.role.value,
        "exp": utcnow() + timedelta(minutes=settings.jwt_expire_minutes),
    }
    return jwt.encode(payload, _require_secret(), algorithm="HS256")


def read_user_id(token: str) -> int:
    try:
        payload = jwt.decode(token, _require_secret(), algorithms=["HS256"])
    except jwt.PyJWTError as exc:
        raise AppError("登录已失效", 401) from exc
    subject = payload.get("sub")
    if not subject:
        raise AppError("登录已失效", 401)
    return int(subject)


def _require_secret() -> str:
    if not _secret:
        raise AppError("认证尚未初始化", 500)
    return _secret


def _b64(raw: bytes) -> str:
    return urlsafe_b64encode(raw).decode().rstrip("=")


def _unb64(text: str) -> bytes:
    padding = "=" * (-len(text) % 4)
    return urlsafe_b64decode(text + padding)