from flask import current_app, request
from flask_login import current_user, login_required
from .. import db, socketio
from ..models import User
import json
import jsonpatch


'''
' A list containing session ids of disconnected Socket.IO sessions. It is used
' to signal associated background tasks to stop.
'''
disconnected = []


@socketio.on('connect')
@login_required
def connect():
    '''
    ' The Socket.IO module creates a session id (sid) on each request. The
    ' initiating client is automatically placed in a room with that sid, which
    ' will be used for further information exchange generated by a background
    ' task associated with the sid.
    '''
    socketio.start_background_task(background_task,
                                   current_app._get_current_object(),
                                   current_user.id,
                                   request.sid)


@socketio.on('disconnect')
@login_required
def disconnect():
    '''
    ' On disconnect the session id (sid) of the connection gets placed in the
    ' disconnected list (see above).
    '''
    disconnected.append(request.sid)


def background_task(app, user_id, session_id):
    '''
    ' Sends initial corpus and job lists to the client. Afterwards it checks
    ' every 3 seconds if changes to the initial values appeared. If changes are
    ' detected, a RFC 6902 compliant JSON patch gets send.
    '
    ' NOTE: The initial values are send as a init-* events.
    '       The JSON patches are send as update-* events.
    '
    '       > where '*' is either 'corpora' or 'jobs'
    '''
    with app.app_context():
        user = db.session.query(User).filter_by(id=user_id).first()
        ''' Get current values from the database. '''
        corpora = user.corpora_as_dict()
        jobs = user.jobs_as_dict()
        ''' Send initial values. '''
        socketio.emit('init-corpora',
                      json.dumps(corpora),
                      room=session_id)
        socketio.emit('init-jobs',
                      json.dumps(jobs),
                      room=session_id)
        ''' TODO: Implement maximum runtime for this loop. '''
        while session_id not in disconnected:
            ''' Get current values from the database '''
            new_corpora = user.corpora_as_dict()
            new_jobs = user.jobs_as_dict()
            ''' Compute JSON patches. '''
            corpus_patch = jsonpatch.JsonPatch.from_diff(corpora, new_corpora)
            jobs_patch = jsonpatch.JsonPatch.from_diff(jobs, new_jobs)
            ''' In case there are patches, send them to the user. '''
            if corpus_patch:
                socketio.emit('update-corpora',
                              corpus_patch.to_string(),
                              room=session_id)
            if jobs_patch:
                socketio.emit('update-jobs',
                              jobs_patch.to_string(),
                              room=session_id)
            ''' Set new values as references for the next iteration. '''
            corpora = new_corpora
            jobs = new_jobs
            socketio.sleep(3)
    disconnected.remove(session_id)