import datetime
import hashlib
import json
import os
import random
import string

import dateutil.parser

from requests_futures.sessions import FuturesSession


TOPIC_URLS = {
    'streams': 'https://api.twitch.tv/helix/streams?user_id={0}',
    'followers': 'https://api.twitch.tv/helix/users/follows?first=1&to_id={0}',
}


class Twitch(object):
    @classmethod
    def subscribe(cls, app, subscriptions, lease_time):
        def read_leases(lease_file):
            result = dict(
                streams=dict(secret=None, valid_until=None, request_hash=None),
                followers=dict(secret=None, valid_until=None, request_hash=None))
            try:
                with open(lease_file) as f:
                    leases = json.load(f)
            except IOError:
                return result
            else:
                result.update(leases)
            return result
        def write_leases(lease_file, leases):
            with open(lease_file, 'w') as f:
                json.dump(leases, f, indent=4, sort_keys=True)
        def generate_secret(length):
            pool = string.ascii_letters + string.digits
            return ''.join(random.SystemRandom().choice(pool) for _ in range(length))
        def sub(topic, secret):
            client_id = os.getenv('TWITCH_CLIENT_ID')
            channel_id = os.getenv('TWITCH_CHANNEL_ID')
            callback_url = os.getenv('CALLBACK_URL')
            session = FuturesSession()
            url = 'https://api.twitch.tv/helix/webhooks/hub'
            headers = {'Client-ID': client_id}
            data = {
                'hub.mode': 'subscribe',
                'hub.topic': TOPIC_URLS[topic].format(channel_id),
                'hub.callback': callback_url,
                'hub.lease_seconds': lease_time,
                'hub.secret': secret,
                }
            h = '{0[hub.mode]}|{0[hub.topic]}|{0[hub.lease_seconds]}'.format(data)
            request_hash = hashlib.sha256(h.encode()).hexdigest()
            return session.post(url, headers=headers, data=data), request_hash
        with app.app_context():
            app.logger.info('Refreshing Twitch subscriptions')
            lease_file = os.getenv('LEASE_FILE')
            leases = read_leases(lease_file)
            for topic, lease in leases.items():
                if not lease['secret'] or not lease['valid_until']:
                    remaining = 0
                if lease['valid_until']:
                    valid_until = dateutil.parser.parse(lease['valid_until'])
                    remaining = (valid_until - datetime.datetime.utcnow()).total_seconds()
                if remaining < 3600:
                    app.logger.info('Subscription "%s" expired, re-requesting', topic)
                    secret = generate_secret(32)
                    valid_until = datetime.datetime.utcnow() + datetime.timedelta(seconds=lease_time)
                    request, request_hash = sub(topic, secret)
                    if request.result().ok:
                        lease['secret'] = secret
                        lease['valid_until'] = valid_until.isoformat()
                        lease['request_hash'] = request_hash
            write_leases(lease_file, leases)
            subscriptions.update(leases)