# -*- coding: utf-8 -*-
"""Module holding utility and convenience functions for zmq event monitoring."""

# Copyright (C) PyZMQ Developers
# Distributed under the terms of the Modified BSD License.

import struct
import zmq
from zmq.error import _check_version

def parse_monitor_message(msg):
    """decode zmq_monitor event messages.
    
    Parameters
    ----------
    msg : list(bytes)
        zmq multipart message that has arrived on a monitor PAIR socket.
        
        First frame is::
        
            16 bit event id
            32 bit event value
            no padding

        Second frame is the endpoint as a bytestring

    Returns
    -------
    event : dict
        event description as dict with the keys `event`, `value`, and `endpoint`.
    """
    
    if len(msg) != 2 or len(msg[0]) != 6:
        raise RuntimeError("Invalid event message format: %s" % msg)
    event = {}
    event['event'], event['value'] = struct.unpack("=hi", msg[0])
    event['endpoint'] = msg[1]
    return event

def recv_monitor_message(socket, flags=0):
    """Receive and decode the given raw message from the monitoring socket and return a dict.

    Requires libzmq ≥ 4.0

    The returned dict will have the following entries:
      event     : int, the event id as described in libzmq.zmq_socket_monitor
      value     : int, the event value associated with the event, see libzmq.zmq_socket_monitor
      endpoint  : string, the affected endpoint
    
    Parameters
    ----------
    socket : zmq PAIR socket
        The PAIR socket (created by other.get_monitor_socket()) on which to recv the message
    flags : bitfield (int)
        standard zmq recv flags

    Returns
    -------
    event : dict
        event description as dict with the keys `event`, `value`, and `endpoint`.
    """
    _check_version((4,0), 'libzmq event API')
    # will always return a list
    msg = socket.recv_multipart(flags)
    # 4.0-style event API
    return parse_monitor_message(msg)

__all__ = ['parse_monitor_message', 'recv_monitor_message']
