#!/usr/bin/env python
# vim: set sw=4 et:
import os
import sys
import argparse
import logging
import socket
import umbra
from kombu import Connection, Exchange, Queue

arg_parser = argparse.ArgumentParser(prog=os.path.basename(__file__),
        description='drain-queue - consume messages from AMQP queue',
        formatter_class=argparse.ArgumentDefaultsHelpFormatter)
arg_parser.add_argument('-u', '--url', dest='amqp_url', default='amqp://guest:guest@localhost:5672/%2f',
        help='URL identifying the AMQP server to talk to')
arg_parser.add_argument('--exchange', dest='amqp_exchange', default='umbra',
        help='AMQP exchange name')
arg_parser.add_argument('--queue', dest='amqp_queue', default='urls',
        help='AMQP queue name')
arg_parser.add_argument('-n', '--no-ack', dest='no_ack', action="store_const",
        default=False, const=True, help="leave messages on the queue (default: remove them from the queue)")
arg_parser.add_argument('-r', '--run-forever', dest='run_forever', action="store_const",
        default=False, const=True, help="run forever, waiting for new messages to appear on the queue (default: exit when all messages in the queue have been consumed)")
arg_parser.add_argument('-v', '--verbose', dest='log_level',
        action="store_const", default=logging.INFO, const=logging.DEBUG)
arg_parser.add_argument('--version', action='version',
        version="umbra {} - {}".format(umbra.version, os.path.basename(__file__)))
args = arg_parser.parse_args(args=sys.argv[1:])

logging.basicConfig(stream=sys.stderr, level=args.log_level,
        format='%(asctime)s %(process)d %(levelname)s %(threadName)s %(name)s.%(funcName)s(%(filename)s:%(lineno)d) %(message)s')

def print_and_maybe_ack(body, message):
    # do this instead of print(body) so that output syntax is json, not python
    # dict (they are similar but not identical)
    print(message.body.decode('utf-8'))

    if not args.no_ack:
        message.ack()

exchange = Exchange(args.amqp_exchange, 'direct', durable=True)
queue = Queue(args.amqp_queue, exchange=exchange)
try:
    with Connection(args.amqp_url) as conn:
        with conn.Consumer(queue, callbacks=[print_and_maybe_ack]) as consumer:
            consumer.qos(prefetch_count=1)
            while True:
                try:
                    conn.drain_events(timeout=0.5)
                except socket.timeout:
                    if not args.run_forever:
                        logging.debug("exiting, no messages left on the queue")
                        break
except KeyboardInterrupt:
    logging.debug("exiting, stopped by user")