from flask import current_app, request
from flask_login import current_user
from . import db, socketio
from .decorators import socketio_admin_required, socketio_login_required
from .models import User
import json
import jsonpatch


'''
' A list containing session ids of connected Socket.IO sessions, to keep track
' of all connected sessions, which is used to determine the runtimes of
' associated background tasks.
'''
connected_sessions = []


@socketio.on('connect')
def connect():
    '''
    ' The Socket.IO module creates a session id (sid) for each request.
    ' On connect the sid is saved in the connected sessions list.
    '''
    connected_sessions.append(request.sid)


@socketio.on('disconnect')
def disconnect():
    '''
    ' On disconnect the session id gets removed from the connected sessions
    ' list.
    '''
    connected_sessions.remove(request.sid)


@socketio.on('start_user_session')
@socketio_login_required
def start_user_session(user_id):
    if not (current_user.id == user_id or current_user.is_administrator):
        return
    socketio.start_background_task(user_session,
                                   current_app._get_current_object(),
                                   user_id, request.sid)


def user_session(app, user_id, session_id):
    '''
    ' Sends initial user data to the client. Afterwards it checks every 3s if
    ' changes to the initial values appeared. If changes are detected, a
    ' RFC 6902 compliant JSON patch gets send.
    '''
    init_event = 'user_{}_init'.format(user_id)
    patch_event = 'user_{}_patch'.format(user_id)
    with app.app_context():
        # Gather current values from database.
        user = User.query.get(user_id)
        user_dict = user.to_dict()
        # Send initial values to the client.
        socketio.emit(init_event, json.dumps(user_dict), room=session_id)
        while session_id in connected_sessions:
            # Get new values from the database
            db.session.refresh(user)
            new_user_dict = user.to_dict()
            # Compute JSON patches.
            user_patch = jsonpatch.JsonPatch.from_diff(user_dict,
                                                       new_user_dict)
            # In case there are patches, send them to the client.
            if user_patch:
                socketio.emit(patch_event, user_patch.to_string(),
                              room=session_id)
            # Set new values as references for the next iteration.
            user_dict = new_user_dict
            socketio.sleep(3)