import datetime
import os
import sys

import boto3
from botocore.exceptions import ClientError

APP_NAME = os.environ.get('APP_NAME')
ENV = os.environ.get('ENV')
ITEMS_TO_INVALIDATE = os.environ.get(
    'ITEMS_TO_INVALIDATE', '/index.html').split(',')


def create_invalidation(client, distribution, items):
    """
    Create an invalidation for a Cloudfront distribution

    Args:
        client (obj): a boto3 Cloudfront client
        distribution (str): a Cloudfront distribution ID

    Returns:
        dict: an invalidation
    """
    try:
        response = client.create_invalidation(
            DistributionId=distribution,
            InvalidationBatch={
                'Paths': {
                    'Quantity': len(items),
                    'Items': items
                },
                'CallerReference': datetime.datetime.now().strftime(
                    '%Y%m%d%H%M%S')
            }
        )
    except ClientError as error:
        print(error.response['Error']['Message'])
        raise SystemExit(f'Error creating invalidation for {distribution}')

    return response['Invalidation']


def find_distributions_to_invalidate(client):
    """
    Find distributions to invalidate based on ENV, with which the distribution
    description/comment should start, and APP_NAME, which should match the
    origin path of one or more origins in a given distribution

    Args:
        client (obj): a boto3 Cloudfront client

    Returns:
        Response: a dict of label information.
    """
    distributions_to_invalidate = []
    response = client.list_distributions()

    distributions = response['DistributionList']['Items']
    for distribution in distributions:
        origin_paths = [origin['OriginPath'] for origin in distribution[
            'Origins']['Items']]
        if any(APP_NAME in origin_path for origin_path in origin_paths) and \
           distribution['Comment'].startswith(ENV):
            distributions_to_invalidate.append(distribution['Id'])
    if distributions_to_invalidate:
        print('Distributions to invalidate: {}'.format(
            distributions_to_invalidate))
        return distributions_to_invalidate
    else:
        print('No distributions found for {}'.format(APP_NAME))
        sys.exit(0)


def main():
    assert APP_NAME, 'Environment variable APP_NAME must be set'
    assert ENV, 'Environment variable ENV must be set'
    client = boto3.client('cloudfront')

    for index, item in enumerate(ITEMS_TO_INVALIDATE):
        # Paths must start with a '/'
        if not item.startswith('/'):
            ITEMS_TO_INVALIDATE[index] = '/' + item
    print('Items to invalidate:{}'.format(ITEMS_TO_INVALIDATE))

    invalidation_distributions = find_distributions_to_invalidate(client)
    for distribution in invalidation_distributions:
        invalidation = create_invalidation(
            client, distribution, ITEMS_TO_INVALIDATE)
        print('Invalidation created for {}; ID: {}, Status: {}'.format(
            distribution, invalidation['Id'], invalidation['Status']))


if __name__ == "__main__":
    main()