#!/usr/bin/env python3
#
# Example 1-1 call signalling server
#
# Copyright (C) 2017 Centricular Ltd.
#
#  Author: Nirbheek Chauhan <nirbheek@centricular.com>
#

import os
import sys
import ssl
import logging
import asyncio
import websockets
import argparse

from concurrent.futures._base import TimeoutError

parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument('--addr', default='0.0.0.0', help='Address to listen on')
parser.add_argument('--port', default=8443, type=int, help='Port to listen on')
parser.add_argument('--keepalive-timeout', dest='keepalive_timeout', default=30, type=int, help='Timeout for keepalive (in seconds)')
parser.add_argument('--cert-path', default=os.path.dirname(__file__))

options = parser.parse_args(sys.argv[1:])

ADDR_PORT = (options.addr, options.port)
KEEPALIVE_TIMEOUT = options.keepalive_timeout

# Format: {uid: (Peer WebSocketServerProtocol, remote_address)}
peers = dict()
# Format: {caller_uid: callee_uid,
#          callee_uid: caller_uid}
# Bidirectional mapping between the two peers
sessions = dict()

############### Helper functions ###############

async def recv_msg_ping(ws, raddr):
    '''
    Wait for a message forever, and send a regular ping to prevent bad routers
    from closing the connection.
    '''
    msg = None
    while msg is None:
        try:
            msg = await asyncio.wait_for(ws.recv(), KEEPALIVE_TIMEOUT)
        except TimeoutError:
            print('Sending keepalive ping to {!r} in recv'.format(raddr))
            await ws.ping()
    return msg

async def disconnect(ws, peer_id):
    '''
    Remove @peer_id from the list of sessions and close our connection to it.
    This informs the peer that the session and all calls have ended, and it
    must reconnect.
    '''
    global sessions
    if peer_id in sessions:
        del sessions[peer_id]
    # Close connection
    if ws and ws.open:
        # Don't care about errors
        asyncio.ensure_future(ws.close(reason='hangup'))

async def remove_peer(uid):
    if uid in sessions:
        other_id = sessions[uid]
        del sessions[uid]
        print("Cleaned up {} session".format(uid))
        if other_id in sessions:
            del sessions[other_id]
            print("Also cleaned up {} session".format(other_id))
            # If there was a session with this peer, also
            # close the connection to reset its state.
            if other_id in peers:
                print("Closing connection to {}".format(other_id))
                wso, oaddr = peers[other_id]
                del peers[other_id]
                await wso.close()
    if uid in peers:
        ws, raddr = peers[uid]
        del peers[uid]
        await ws.close()
        print("Disconnected from peer {!r} at {!r}".format(uid, raddr))

############### Handler functions ###############

async def connection_handler(ws, peer_id):
    global peers, sessions
    raddr = ws.remote_address
    peers[peer_id] = (ws, raddr)
    print("Registered peer {!r} at {!r}".format(peer_id, raddr))
    while True:
        # Receive command, wait forever if necessary
        msg = await recv_msg_ping(ws, raddr)
        if msg.startswith('SESSION'):
            print("{!r} command {!r}".format(peer_id, msg))
            _, callee_id = msg.split(maxsplit=1)
            if callee_id not in peers:
                await ws.send('ERROR peer {!r} not found'.format(callee_id))
                continue
            if callee_id in sessions:
                await ws.send('ERROR peer {!r} busy'.format(callee_id))
                continue
            await ws.send('SESSION_OK')
            wsc = peers[callee_id][0]
            print("Session from {!r} ({!r}) to {!r} ({!r})".format(peer_id, raddr, callee_id,
                                                                    wsc.remote_address))
            # Register call
            sessions[peer_id] = callee_id
            sessions[callee_id] = peer_id
        # We're in a session, route message to connected peer
        elif peer_id in sessions:
            other_id = sessions[peer_id]
            wso, oaddr = peers[other_id]
            print("{} -> {}: {}".format(peer_id, other_id, msg))
            await wso.send(msg)

async def hello_peer(ws):
    '''
    Exchange hello, register peer
    '''
    raddr = ws.remote_address
    hello = await ws.recv()
    hello, uid = hello.split(maxsplit=1)
    if hello != 'HELLO':
        await ws.close(code=1002, reason='invalid protocol')
        raise Exception("Invalid hello from {!r}".format(raddr))
    if not uid or uid in peers:
        await ws.close(code=1002, reason='invalid peer uid')
        raise Exception("Invalid uid {!r} from {!r}".format(uid, raddr))
    # Send back a HELLO
    await ws.send('HELLO')
    return uid

async def handler(ws, path):
    '''
    All incoming messages are handled here. @path is unused.
    '''
    raddr = ws.remote_address
    print("Connected to {!r}".format(raddr))
    peer_id = await hello_peer(ws)
    try:
        await connection_handler(ws, peer_id)
    except websockets.ConnectionClosed:
        print("Connection to peer {!r} closed, exiting handler".format(raddr))
    finally:
        await remove_peer(peer_id)

# Create an SSL context to be used by the websocket server
certpath = options.cert_path
print('Using TLS with keys in {!r}'.format(certpath))
if 'letsencrypt' in certpath:
    chain_pem = os.path.join(certpath, 'fullchain.pem')
    key_pem = os.path.join(certpath, 'privkey.pem')
else:
    chain_pem = os.path.join(certpath, 'cert.pem')
    key_pem = os.path.join(certpath, 'key.pem')

sslctx = ssl.create_default_context()
try:
    sslctx.load_cert_chain(chain_pem, keyfile=key_pem)
except FileNotFoundError:
    print("Certificates not found, did you run generate_cert.sh?")
    sys.exit(1)
# FIXME
sslctx.check_hostname = False
sslctx.verify_mode = ssl.CERT_NONE

print("Listening on https://{}:{}".format(*ADDR_PORT))
# Websocket server
wsd = websockets.serve(handler, *ADDR_PORT, ssl=sslctx,
                       # Maximum number of messages that websockets will pop
                       # off the asyncio and OS buffers per connection. See:
                       # https://websockets.readthedocs.io/en/stable/api.html#websockets.protocol.WebSocketCommonProtocol
                       max_queue=16)

logger = logging.getLogger('websockets.server')

logger.setLevel(logging.ERROR)
logger.addHandler(logging.StreamHandler())

asyncio.get_event_loop().run_until_complete(wsd)
asyncio.get_event_loop().run_forever()