# -*- coding: utf-8 -*-
# !/usr/bin/env python

import base64
import hashlib
import hmac
import simplejson as json
import time
import uuid

from cryptography.exceptions import InvalidSignature, InvalidTag
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric.padding import MGF1, OAEP, PKCS1v15
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
from cryptography.hazmat.primitives.hashes import SHA1, SHA256
from cryptography.hazmat.primitives.serialization import load_pem_private_key
from cryptography.x509 import load_pem_x509_certificate


def build_authorization(path, method, mchid, serial_no, private_key, data = None, nonce_str = None):
    timeStamp = str(int(time.time()))
    nonce_str = nonce_str or ''.join(str(uuid.uuid4()).split('-')).upper()

    data = data or data or ""
    body = json.dumps(data) if not isinstance(data, basestring) else data

    sign_str = '%s\n%s\n%s\n%s\n%s\n' % (method, path, timeStamp, nonce_str, body)
    signature = rsa_sign(private_key = private_key, sign_str = sign_str)

    authorization = 'WECHATPAY2-SHA256-RSA2048 mchid="%s",nonce_str="%s",signature="%s",timestamp="%s",serial_no="%s"' % (
        mchid, nonce_str, signature, timeStamp, serial_no)
    return authorization


def rsa_sign(private_key, sign_str):
    message = sign_str.encode('utf-8')

    signature = private_key.sign(data = message, padding = PKCS1v15(), algorithm = SHA256())
    sign = base64.b64encode(signature).decode('utf8').replace('\n', '')
    return sign


def aes_decrypt(nonce, ciphertext, associated_data, apiv3_key):
    key_bytes = apiv3_key.encode('UTF-8')
    nonce_bytes = nonce.encode('UTF-8')
    associated_data_bytes = associated_data.encode('UTF-8')
    data = base64.b64decode(ciphertext)
    aesgcm = AESGCM(key = key_bytes)
    try:
        result = aesgcm.decrypt(nonce = nonce_bytes, data = data, associated_data = associated_data_bytes).decode(
            'UTF-8')
    except InvalidTag:
        result = None
    return result


def format_private_key(private_key_str):
    pem_start = '-----BEGIN PRIVATE KEY-----\n'
    pem_end = '\n-----END PRIVATE KEY-----'
    if not private_key_str.startswith(pem_start):
        private_key_str = pem_start + private_key_str
    if not private_key_str.endswith(pem_end):
        private_key_str = private_key_str + pem_end
    return private_key_str


def load_certificate(certificate_str):
    """加载证书字符串"""
    try:
        return load_pem_x509_certificate(data = certificate_str.encode('UTF-8'), backend = default_backend())
    except:
        return None


def load_private_key(private_key_str):
    try:
        return load_pem_private_key(data = format_private_key(private_key_str).encode('UTF-8'), password = None,
                                    backend = default_backend())
    except:
        raise Exception('failed to load private key.')


def rsa_verify(timestamp, nonce, body, signature, certificate):
    sign_str = '%s\n%s\n%s\n' % (timestamp, nonce, body)
    public_key = certificate.public_key()
    message = sign_str.encode('UTF-8')
    signature = base64.b64decode(signature)
    try:
        public_key.verify(signature, message, PKCS1v15(), SHA256())
    except InvalidSignature:
        return False
    return True


def rsa_encrypt(text, certificate):
    data = text.encode('UTF-8')
    public_key = certificate.public_key()
    cipherbyte = public_key.encrypt(
        plaintext = data,
        padding = OAEP(mgf = MGF1(algorithm = SHA1()), algorithm = SHA1(), label = None)
    )
    return base64.b64encode(cipherbyte).decode('UTF-8')


def rsa_decrypt(ciphertext, private_key):
    data = private_key.decrypt(
        ciphertext = base64.b64decode(ciphertext),
        padding = OAEP(mgf = MGF1(algorithm = SHA1()), algorithm = SHA1(), label = None)
    )
    result = data.decode('UTF-8')
    return result


def hmac_sign(key, sign_str):
    return hmac.new(key.encode('UTF-8'), msg = sign_str, digestmod = hashlib.sha256).hexdigest().upper()


def sha256(data):
    return hashlib.sha256(data).hexdigest()