# -*- coding: utf-8 -*-
"""OpenAPI 签名：空值不参与，字典序，MD5 小写。"""
from __future__ import annotations

import hashlib
from typing import Any, Mapping


def build_sign(params: Mapping[str, Any], secret_key: str) -> str:
    items = []
    for k in sorted(params.keys()):
        if k == "Sign":
            continue
        v = params[k]
        if v is None:
            continue
        s = str(v)
        if s == "":
            continue
        items.append(f"{k}={s}")
    raw = "&".join(items) + f"&SecretKey={secret_key}"
    return hashlib.md5(raw.encode("utf-8")).hexdigest()