#! /usr/bin/python3

"""Open Debian BTS mboxes with Mutt, à la /usr/bin/bts show --mbox.

A cache of mboxes is kept, and changed mboxes will be merged with existing
files instead of replacing them, so that e.g. read-status is preserved for each
message.
"""

import os
import re
import sys
import mailbox
import tempfile
import email.parser
import urllib.request

MBOX_DIR = os.path.expanduser('~/.mail/y.bug-cache')

##

def main():
    if len(sys.argv) != 2:
        print('Usage: {0} <bugnumber>'.format(sys.argv[0]), file=sys.stderr)
        return 1
    else:
        bug = re.sub(r'[^0-9]', '', sys.argv[1])

    if not re.search(r'^\d{4,}$', bug):
        print('E: {0} does not seem a valid number'.format(sys.argv[1]),
              file=sys.stderr)
        return 1

    path = mbox_update(bug)
    invoke_mailer(path)

##

def mbox_update(bug):
    """Return a path with an up-to-date copy of the mbox for bug."""
    path = os.path.join(MBOX_DIR, bug + '.mbox')

    if not os.path.exists(path):
        f = open(path, 'wb')
        try:
            retrieve_mbox(bug, f)
        except:
            os.unlink(path)
            raise
        else:
            f.close()
    else:
        # make a list of Message-Id we have
        msgids = { x.get('Message-Id') for x in mailbox.mbox(path) }

        with tempfile.NamedTemporaryFile() as tmpfd:
            # retrieve the remote mbox again
            retrieve_mbox(bug, tmpfd)

            # parse its messages
            parser = email.parser.Parser()
            new_msgids = { x['Message-Id']: x
                            for x in mailbox.mbox(tmpfd.name, parser.parse) }

        with open(path, 'a+') as fd:
            # now append the new messages
            for msgid in new_msgids.keys() - msgids:
                fd.write('\n' + new_msgids[msgid].as_string(unixfrom=True))

    return path

def retrieve_mbox(bug, fileobj):
    """Retrieve mbox for bug from bugs.debian.org, writing it to fileobj."""
    url = urllib.request.urlopen(
            'http://bugs.debian.org/cgi-bin/bugreport.cgi?'
            'mboxstatus=yes;mboxmaint=yes;mbox=yes;bug={0}'.format(bug))
    for line in url.fp: # http://bugs.python.org/issue4608
        fileobj.write(line)

def invoke_mailer(path):
    """Exec mutt, opening path."""
    os.execlp('mutt', 'mutt', '-f', path)

##

if __name__ == '__main__':
    try:
        sys.exit(main())
    except KeyboardInterrupt:
        print('\nCancelled.', file=sys.stderr)
        sys.exit(1)