#!/usr/bin/env python
"""
github_buildbot.py is based on git_buildbot.py. Last revised on 2014-02-20.

github_buildbot.py will determine the repository information from the JSON
HTTP POST it receives from github.com and build the appropriate repository.
If your github repository is private, you must add a ssh key to the github
repository for the user who initiated the build on the buildslave.

This version of github_buildbot.py parses v3 of the github webhook api, with the
"application.vnd.github.v3+json" payload. Configure *only* "push" and/or
"pull_request" events to trigger this webhook.

"""

import hmac
import logging
import os
import re
import sys

from hashlib import sha1
from httplib import ACCEPTED
from httplib import BAD_REQUEST
from httplib import INTERNAL_SERVER_ERROR
from httplib import OK
from optparse import OptionParser

from twisted.cred import credentials
from twisted.internet import reactor
from twisted.spread import pb
from twisted.web import resource
from twisted.web import server

try:
    import json
except ImportError:
    import simplejson as json


class GitHubBuildBot(resource.Resource):

    """
    GitHubBuildBot creates the webserver that responds to the GitHub Service
    Hook.
    """
    isLeaf = True
    master = None
    port = None

    def render_POST(self, request):
        """
        Responds only to POST events and starts the build process

        :arguments:
            request
                the http request object
        """

        # All responses are application/json
        request.setHeader("Content-Type", "application/json")

        content = request.content.read()

        # Verify the message if a secret was provided
        #
        # NOTE: We always respond with '400 BAD REQUEST' if we can't
        # validate the message.  This is done to prevent malicious
        # requests from learning about why they failed to POST data
        # to us.
        if self.secret is not None:
            signature = request.getHeader("X-Hub-Signature")

            if signature is None:
                logging.error("Rejecting request.  Signature is missing.")
                request.setResponseCode(BAD_REQUEST)
                return json.dumps({"error": "Bad Request."})

            try:
                hash_type, hexdigest = signature.split("=")

            except ValueError:
                logging.error("Rejecting request.  Bad signature format.")
                request.setResponseCode(BAD_REQUEST)
                return json.dumps({"error": "Bad Request."})

            else:
                # sha1 is hard coded into github's source code so it's
                # unlikely this will ever change.
                if hash_type != "sha1":
                    logging.error("Rejecting request.  Unexpected hash type.")
                    request.setResponseCode(BAD_REQUEST)
                    return json.dumps({"error": "Bad Request."})

                mac = hmac.new(self.secret, msg=content, digestmod=sha1)
                if mac.hexdigest() != hexdigest:
                    logging.error("Rejecting request.  Hash mismatch.")
                    request.setResponseCode(BAD_REQUEST)
                    return json.dumps({"error": "Bad Request."})

        event_type = request.getHeader("X-GitHub-Event")
        logging.debug("X-GitHub-Event: %r", event_type)

        handler = getattr(self, 'handle_%s' % event_type, None)

        if handler is None:
            logging.info(
                "Rejecting request. Received unsupported event %r.",
                event_type)
            request.setResponseCode(BAD_REQUEST)
            return json.dumps({"error": "Bad Request."})

        try:
            content_type = request.getHeader("Content-Type")

            if content_type == "application/json":
                payload = json.loads(content)
            elif content_type == "application/x-www-form-urlencoded":
                payload = json.loads(request.args["payload"][0])
            else:
                logging.info(
                    "Rejecting request.  Unknown 'Content-Type', received %r",
                    content_type)
                request.setResponseCode(BAD_REQUEST)
                return json.dumps({"error": "Bad Request."})

            logging.debug("Payload: %r", payload)
            repo = payload['repository']['full_name']
            repo_url = payload['repository']['html_url']
            changes = handler(payload, repo, repo_url)
            self.send_changes(changes, request)
            return server.NOT_DONE_YET

        except Exception, e:
            logging.exception(e)
            request.setResponseCode(INTERNAL_SERVER_ERROR)
            return json.dumps({"error": e.message})

    def process_change(self, change, branch, repo, repo_url):
        files = change['added'] + change['removed'] + change['modified']
        who = ""
        if 'username' in change['author']:
            who = change['author']['username']
        else:
            who = change['author']['name']
        if 'email' in change['author']:
            who = "%s <%s>" % (who, change['author']['email'])

        comments = change['message']
        if len(comments) > 1024:
            trim = " ... (trimmed, commit message exceeds 1024 characters)"
            comments = comments[:1024 - len(trim)] + trim

        return \
            {'revision': change['id'],
             'revlink': change['url'],
             'who': who,
             'comments': comments,
             'repository': repo_url,
             'files': files,
             'project': repo,
             'branch': branch}

    def handle_ping(self, *_):
        return None

    def handle_push(self, payload, repo, repo_url):
        """
        Consumes the JSON as a python object and actually starts the build.

        :arguments:
            payload
                Python Object that represents the JSON sent by GitHub Service
                Hook.
        """
        changes = None
        refname = payload['ref']

        m = re.match(r"^refs\/(heads|tags)\/(.+)$", refname)
        if not m:
            logging.info(
                "Ignoring refname `%s': Not a branch or a tag", refname)
            return changes

        refname = m.group(2)

        if payload['deleted'] is True:
            logging.info("%r deleted, ignoring", refname)
        else:
            changes = []
            for change in payload['commits']:
                if (self.head_commit or m.group(1) == 'tags') \
                        and change['id'] != payload['head_commit']['id']:
                    continue
                changes.append(self.process_change(
                    change, refname, repo, repo_url))
        return changes

    def handle_pull_request(self, payload, repo, repo_url):
        """
        Consumes the JSON as a python object and actually starts the build.

        :arguments:
            payload
                Python Object that represents the JSON sent by GitHub Service
                Hook.
        """
        changes = None

        branch = "refs/pull/{}/head".format(payload['number'])

        if payload['action'] not in ("opened", "synchronize"):
            logging.info("PR %r %r, ignoring",
                         payload['number'], payload['action'])
            return None
        else:
            changes = []

            # Create a synthetic change
            change = {
                'id': payload['pull_request']['head']['sha'],
                'message': payload['pull_request']['body'],
                'timestamp': payload['pull_request']['updated_at'],
                'url': payload['pull_request']['html_url'],
                'author': {
                    'username': payload['pull_request']['user']['login'],
                },
                'added': [],
                'removed': [],
                'modified': [],
            }

            changes.append(self.process_change(
                change, branch, repo, repo_url))
        return changes

    def send_changes(self, changes, request):
        """
        Submit the changes, if any
        """
        if not changes:
            logging.warning("No changes found")
            request.setResponseCode(OK)
            request.write(json.dumps({"result": "No changes found."}))
            request.finish()
            return

        host, port = self.master.split(':')
        port = int(port)

        if self.auth is not None:
            auth = credentials.UsernamePassword(*self.auth.split(":"))
        else:
            auth = credentials.Anonymous()

        factory = pb.PBClientFactory()
        deferred = factory.login(auth)
        reactor.connectTCP(host, port, factory)
        deferred.addErrback(self.connectFailed, request)
        deferred.addCallback(self.connected, changes, request)

    def connectFailed(self, error, request):
        """
        If connection is failed.  Logs the error.
        """
        logging.error("Could not connect to master: %s",
                      error.getErrorMessage())
        request.setResponseCode(INTERNAL_SERVER_ERROR)
        request.write(
            json.dumps({"error": "Failed to connect to buildbot master."}))
        request.finish()
        return error

    def addChange(self, _, remote, changei, src='git'):
        """
        Sends changes from the commit to the buildmaster.
        """
        logging.debug("addChange %r, %r", remote, changei)
        try:
            change = changei.next()
        except StopIteration:
            remote.broker.transport.loseConnection()
            return None

        logging.info("New revision: %s", change['revision'][:8])
        for key, value in change.iteritems():
            logging.debug("  %s: %s", key, value)

        change['src'] = src
        deferred = remote.callRemote('addChange', change)
        deferred.addCallback(self.addChange, remote, changei, src)
        return deferred

    def connected(self, remote, changes, request):
        """
        Responds to the connected event.
        """
        # By this point we've connected to buildbot so
        # we don't really need to keep github waiting any
        # longer
        request.setResponseCode(ACCEPTED)
        request.write(json.dumps({"result": "Submitting changes."}))
        request.finish()

        return self.addChange(None, remote, changes.__iter__())


def setup_options():
    """
    The main event loop that starts the server and configures it.
    """
    usage = "usage: %prog [options]"
    parser = OptionParser(usage)

    parser.add_option("-p", "--port",
                      help="Port the HTTP server listens to for the GitHub "
                           "Service Hook [default: %default]",
                      default=9001, type=int, dest="port")

    parser.add_option("-m", "--buildmaster",
                      help="Buildbot Master host and port. ie: localhost:9989 "
                           "[default: %default]",
                      default="localhost:9989", dest="buildmaster")

    parser.add_option("--auth",
                      help="The username and password, separated by a colon, "
                           "to use when connecting to buildbot over the "
                           "perspective broker.",
                      default="change:changepw", dest="auth")

    parser.add_option("--head-commit", action="store_true",
                      help="If set, only trigger builds for commits at head")

    parser.add_option("--secret",
                      help="If provided then use the X-Hub-Signature header "
                           "to verify that the request is coming from "
                           "github. [default: %default]",
                      default=None, dest="secret")

    parser.add_option("-l", "--log",
                      help="The absolute path, including filename, to save the "
                           "log to [default: %default].  This may also be "
                           "'stdout' indicating logs should output directly to "
                           "standard output instead.",
                      default="github_buildbot.log", dest="log")

    parser.add_option("-L", "--level",
                      help="The logging level: debug, info, warn, error, "
                           "fatal [default: %default]", default='warn',
                      dest="level",
                      choices=("debug", "info", "warn", "error", "fatal"))

    parser.add_option("-g", "--github",
                      help="The github server.  Changing this is useful if"
                           " you've specified a specific HOST handle in "
                           "~/.ssh/config for github [default: %default]",
                      default='github.com', dest="github")

    parser.add_option("--pidfile",
                      help="Write the process identifier (PID) to this "
                           "file on start. The file is removed on clean "
                           "exit. [default: %default]",
                      default=None, dest="pidfile")

    (options, _) = parser.parse_args()

    if options.auth is not None and ":" not in options.auth:
        parser.error("--auth did not contain ':'")

    if options.pidfile:
        with open(options.pidfile, 'w') as f:
            f.write(str(os.getpid()))

    filename = options.log
    log_format = "%(asctime)s - %(levelname)s - %(message)s"
    if options.log != "stdout":
        logging.basicConfig(filename=filename, format=log_format,
                            level=logging._levelNames[options.level.upper()])
    else:
        logging.basicConfig(format=log_format,
                            handlers=[logging.StreamHandler(stream=sys.stdout)],
                            level=logging._levelNames[options.level.upper()])

    return options


def run_hook(options):
    github_bot = GitHubBuildBot()
    github_bot.github = options.github
    github_bot.master = options.buildmaster
    github_bot.secret = options.secret
    github_bot.auth = options.auth
    github_bot.head_commit = options.head_commit

    site = server.Site(github_bot)
    reactor.listenTCP(options.port, site)

    reactor.run()


def main():
    options = setup_options()

    run_hook(options)


if __name__ == '__main__':
    main()
