import sys
import mailbox

VERBOSE = 1
def log(*args):
    if not VERBOSE:
        return
    print('| ' + ''.join(str(i) for i in args), file=sys.stderr)

class MailboxHelper:
    @staticmethod
    def open(path, type='mbox', create=False):
        log('Opening ', type, ' mailbox ', path)
        if type == 'mbox':
            mb = mailbox.mbox
        elif type == 'maildir':
            mb = mailbox.Maildir
        #try:
        mb = mb(path, create=create)
        #except Exception:
            # FIXME throws IOError (Errno 21) if dispatch specified a dir but
            # dod not set a dir-based type..
        #    panic('Failed to open ', path, extb=E())
        return mb

msg = None

inmb = MailboxHelper.open('input.mdir', type='maildir', create=False)
try:
    log('* Box has ', len(inmb),
        ' messages, filtering through rulesets')
    cnt = 0
    for k in inmb.iterkeys():
        cnt += 1
        log('({!s:>04})'.format(cnt))
        msg = inmb.get_message(k)
        if cnt == 1:
            break
except Exception as e:
    error('failed to handle box ', b, extb=E())


outmb = MailboxHelper.open('output.mbox', create=True)
try:
    outmb.add(msg)
    outmb.flush()
except Exception as e:
    log(': message-add failed.\n')
    raise
finally:
    outmb.unlock()