import base64
import json
from pathlib import Path

from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives.serialization import load_pem_private_key

from app.core.config import configured_path


MANIFEST_PRIVATE_KEY_PATH = str(configured_path("MANIFEST_PRIVATE_KEY_PATH", "keys/manifest_private_key.pem"))


def load_manifest_private_key():
    key_path = Path(MANIFEST_PRIVATE_KEY_PATH)
    if not key_path.exists():
        raise FileNotFoundError(f"Manifest private key not found: {key_path}")
    key_data = key_path.read_bytes()
    return load_pem_private_key(key_data, password=None)


def canonical_manifest_bytes(manifest_obj: dict) -> bytes:
    # 签名之前必须先规范化 JSON：固定字段顺序、去掉空格、排除 signature 字段。
    # 否则同一份 Manifest 在不同环境下序列化结果不同，会导致客户端验签失败。
    copy = {k: manifest_obj[k] for k in manifest_obj if k != "signature"}
    return json.dumps(copy, sort_keys=True, separators=(",", ":"), ensure_ascii=False).encode("utf-8")


def sign_manifest(manifest_obj: dict) -> str:
    # 服务端只保存私钥，客户端只分发公钥。
    # 客户端能验证 Manifest 确实由服务端签发，但无法伪造新的签名。
    json_text = canonical_manifest_bytes(manifest_obj)
    private_key = load_manifest_private_key()
    signature = private_key.sign(json_text, padding.PKCS1v15(), hashes.SHA256())
    return base64.b64encode(signature).decode("ascii")


def canonical_signed_bytes(obj: dict) -> bytes:
    copy = {k: obj[k] for k in obj if k != "signature"}
    return json.dumps(copy, sort_keys=True, separators=(",", ":"), ensure_ascii=False).encode("utf-8")


def sign_policy(policy_obj: dict) -> tuple[str, str]:
    payload = canonical_signed_bytes(policy_obj)
    signature = load_manifest_private_key().sign(payload, padding.PKCS1v15(), hashes.SHA256())
    return payload.decode("utf-8"), base64.b64encode(signature).decode("ascii")


def sign_device_identity(identity: dict) -> tuple[str, str]:
    payload = canonical_signed_bytes(identity)
    signature = load_manifest_private_key().sign(payload, padding.PKCS1v15(), hashes.SHA256())
    return payload.decode("utf-8"), base64.b64encode(signature).decode("ascii")