import base64
import hashlib
import os
import secrets
import string

_PBKDF2_ALGO = "sha256"
_PBKDF2_ITERATIONS = 600_000
_PBKDF2_SALT_LEN = 16
_PBKDF2_PREFIX = "$pbkdf2-sha256$"

_STRONG_PWD_CHARS = string.ascii_letters + string.digits + "!@#$%^&*"


class PwdUtil:
    @staticmethod
    def hash_password(password: str) -> str:
        salt = os.urandom(_PBKDF2_SALT_LEN)
        dk = hashlib.pbkdf2_hmac(_PBKDF2_ALGO, password.encode(), salt, _PBKDF2_ITERATIONS)
        return f"{_PBKDF2_PREFIX}{_PBKDF2_ITERATIONS}${base64.b64encode(salt).decode()}${base64.b64encode(dk).decode()}"

    @staticmethod
    def verify_password(plain_password: str, password_hash: str) -> bool:
        try:
            _, _algo, iters_str, salt_b64, hash_b64 = password_hash.split("$")
            salt = base64.b64decode(salt_b64)
            expected = base64.b64decode(hash_b64)
            dk = hashlib.pbkdf2_hmac(_PBKDF2_ALGO, plain_password.encode(), salt, int(iters_str))
            return dk == expected
        except Exception:
            return False

    @staticmethod
    def check_password_strength(password: str) -> str | None:
        if len(password) < 6:
            return "密码长度至少6位"
        if not any(c.isupper() for c in password):
            return "密码需要包含大写字母"
        if not any(c.islower() for c in password):
            return "密码需要包含小写字母"
        if not any(c.isdigit() for c in password):
            return "密码需要包含数字"
        return None

    @staticmethod
    def generate_strong_password(length: int = 12) -> str:
        """生成符合强度要求的强随机密码（大写+小写+数字+特殊符号）。

        使用 ``secrets`` 而非 ``random``，避免伪随机带来的安全风险。

        参数:
        - length (int): 密码长度，默认 12，最小 8。

        返回:
        - str: 生成的明文密码。
        """
        if length < 8:
            raise ValueError("密码长度至少 8 位")

        # 保证每类字符至少出现一次
        uppercase = secrets.choice(string.ascii_uppercase)
        lowercase = secrets.choice(string.ascii_lowercase)
        digit = secrets.choice(string.digits)
        special = secrets.choice("!@#$%^&*")

        remaining_length = length - 4
        rest = [secrets.choice(_STRONG_PWD_CHARS) for _ in range(remaining_length)]

        chars = list(rest) + [uppercase, lowercase, digit, special]
        secrets.SystemRandom().shuffle(chars)
        return "".join(chars)