import argparse
import os
import re
import time

from github import Github


GITHUB_TOKEN = os.getenv('GITHUB_TOKEN')


def get_mergeable_state(pr_number):
    """Get mergeable state of the PR https://docs.github.com/en/graphql/reference/enums#mergestatestatus"""
    github_api = Github(GITHUB_TOKEN)
    db_repo = github_api.get_repo("theorchard/database")

    # github calculates mergeable state when the api request occurs, so might need to retry a fetch if stale
    attempt = 1
    while (attempt < 10):
        pr = db_repo.get_pull(pr_number)
        mergeable_state = pr.mergeable_state

        if mergeable_state != 'unknown':
            return mergeable_state

        print('PR {} status is currently unknown, sleeping and retrying.'.format(
            pr_number))
        time.sleep(5)
        attempt = attempt + 1
    raise Exception('PR {} has a mergeable_state of unknown. Please give '
                    'GitHub a minute to finish calculating this state.'.format(pr_number))
    

def is_pr_mergeable(pr_number, raise_exception):
    pr_mergeable_state = get_mergeable_state(pr_number)
    print('The status of PR {} is {}'.format(pr_number, pr_mergeable_state))
    
    if pr_mergeable_state != 'clean':
        message = 'PR {} is not mergeable, blocking deploy'.format(pr_number)
        if raise_exception:
            raise Exception(message)
        print(message)
        return False
    print('This PR is mergeable')
    return True


def get_pr_state_merged(pr_number):
    github_api = Github(GITHUB_TOKEN)
    db_repo = github_api.get_repo("theorchard/database")
    pr = db_repo.get_pull(pr_number)
    return (pr.state, pr.merged)


def get_pr_from_sha1(sha1):
    github_api = Github(GITHUB_TOKEN)
    db_repo = github_api.get_repo("theorchard/database")
    commit = db_repo.get_commit(sha1)
    pulls = commit.get_pulls()
    return pulls[0].number


def get_pr_from_pr_string(pr_string):
    """pr_string in format of 'refs/remotes/origin/pr/<PR#>/head' """
    pattern = re.compile("refs/remotes/origin/pr/([0-9]+)/head")
    match = pattern.fullmatch(pr_string)
    if match:
        return int(match[1])
    else:
        raise Exception('PR String not in expected format: '
                        'refs/remotes/origin/pr/<PR#>/head')


def main(*args):
    parser = argparse.ArgumentParser()
    parser.add_argument(
        '--pr-number',
        type=int,
        help='Pull Request to check if mergeable')
    parser.add_argument(
        '--pr-string',
        help='refs/remotes/origin/pr/<PR#>/head')
    parser.add_argument(
        '--sha1',
        help='sha1 whose Pull Request to check if mergeable')
    parser.add_argument(
        '--raise-exception',
        action='store_true',
        help='Raise exception if PR is not mergeable')
    args = parser.parse_args()

    pr_number = args.pr_number
    if (args.pr_string):
        pr_number = get_pr_from_pr_string(args.pr_string)
    if (args.sha1):
        pr_number = get_pr_from_sha1(args.sha1)

    # check if PR is already merged (otherwise mergeable state is always unknown)
    (state, merged) = get_pr_state_merged(pr_number)

    if merged:
        print('PR {} is already merged and can be deployed'.format(pr_number))
        return True

    if state == 'closed':
        message = 'PR {} is closed and not merged so canNOT be deployed'.format(pr_number)
        if args.raise_exception:
            raise Exception(message)
        print(message)
        return False

    is_pr_mergeable(pr_number, args.raise_exception)


if __name__ == '__main__':
    main()