signed_requests

# Adapted from: 
# https://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html
import datetime
import hashlib
import hmac
import os

import requests

# ************* REQUEST VALUES *************
def execute(
        method='GET',
        service='execute-api',
        host=None,
        region='eu-west-1',
        path='/',
        endpoint=None,
            request_parameters='',
        access_key = None,
        secret_key = None,
        data: str = '',
        extra_headers = None,
        content_type: str = 'application/json'
):
    if extra_headers is None:
        extra_headers = {}
    if endpoint is None:
        endpoint = f'https://{host}{path}'

    if access_key is None:
        access_key = os.environ.get('SIGNATURE_KEY')
    if secret_key is None:
        secret_key = os.environ.get('SIGNATURE_SECRET')
    if access_key is None or secret_key is None:
        print('No access key is available.')
        raise Exception('No access key is available.')

    # Create a date for headers and the credential string
    t = datetime.datetime.utcnow()
    amzdate = t.strftime('%Y%m%dT%H%M%SZ')
    datestamp = t.strftime('%Y%m%d')  # Date w/o time, used in credential scope

    # Explanation of the steps, see
    # https://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html
    canonical_uri = path
    canonical_querystring = request_parameters

    canonical_headers = 'host:' + host + '\n' + 'x-amz-date:' + amzdate + '\n'
    signed_headers = 'host;x-amz-date'
    if method.upper() == 'POST':
        canonical_headers = 'content-type:' + content_type + '\n' + canonical_headers
        signed_headers = 'content-type;' + signed_headers

    payload_hash = hashlib.sha256(data.encode('utf-8')).hexdigest()
    canonical_request = method + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash
    # print('canonical_request: %s', canonical_request)
    algorithm = 'AWS4-HMAC-SHA256'
    credential_scope = datestamp + '/' + region + '/' + service + '/' + 'aws4_request'
    string_to_sign = algorithm + '\n' + amzdate + '\n' + credential_scope + '\n' + hashlib.sha256(
        canonical_request.encode('utf-8')).hexdigest()
    # print('string_to_sign: %s', string_to_sign)
    signing_key = getSignatureKey(secret_key, datestamp, region, service)
    signature = hmac.new(signing_key, string_to_sign.encode('utf-8'), hashlib.sha256).hexdigest()
    authorization_header = algorithm + ' ' + 'Credential=' + access_key + '/' + credential_scope + ', ' + 'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature
    headers = {
        'x-amz-date': amzdate,
        'Authorization': authorization_header,
        **extra_headers
    }
    if method.upper() == 'POST':
        headers['Content-Type'] = content_type

    request_url = endpoint + '?' + canonical_querystring

    print('\nBEGIN REQUEST++++++++++++++++++++++++++++++++++++')
    print('Request URL = ' + request_url)
    print('Request HEADERS = ' + str(headers))
    if method.upper() == 'GET':
        r = requests.get(request_url, headers=headers)
    elif method.upper() == 'POST':
        r = requests.post(url=request_url, data=data, headers=headers)
    elif method.upper() == 'PUT':
        r = requests.put(url=request_url, data=data, headers=headers)
    elif method.upper() == 'DELETE':
        r = requests.delete(url=request_url, data=data, headers=headers)
    else:
        raise Exception(f'Unsupported method "{method}"')

    print('\nRESPONSE++++++++++++++++++++++++++++++++++++')
    print('Response code: %d\n' % r.status_code)
    print(r.text)
    return r


# Key derivation functions. See:
# http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python
def sign(key, msg):
    return hmac.new(key, msg.encode('utf-8'), hashlib.sha256).digest()


def getSignatureKey(key, dateStamp, regionName, serviceName):
    kDate = sign(('AWS4' + key).encode('utf-8'), dateStamp)
    kRegion = sign(kDate, regionName)
    kService = sign(kRegion, serviceName)
    kSigning = sign(kService, 'aws4_request')
    return kSigning