const mysql = require('mysql');

const pool = mysql.createPool({
    host: 'localhost',
    user: 'user',
    password: 'pass',
    database: 'db_name'
});

pool.connect(function (err) {
    if (err) {
        throw err;
    }
    console.log("SQL Connected!");
});

const platformFollowersParsers = {
    'YouTube': function () {
        const serviceId = 5;
        var flag = true;

        while (true) {
            if (flag) {
                getPlatfromChannelsForParsing(serviceId)
                    .then(parseYouTubeChannels)
                    .then(writeResultToDB)
                    .then(shouldContinue => {
                        if (!shouldContinue) {
                            flag = false;
                            getOldestChangedChannel(serviceId,
                                function (errorFromDB, oldestChannel) {
                                    if (errorFromDB) {
                                        console.log(errorFromDB);
                                        // if error try in 60minutes
                                        waitMilliseconds(1000 * 60 * 60, () => flag = true);
                                    } else {
                                        // try in 24hours after oldest change
                                        var dayAfterOldestChange = (oldestChannel['last_change_followers_count'] -
                                                                    Date.now()) +
                                                                   1000 * 60 * 60 * 24;
                                        waitMilliseconds(dayAfterOldestChange, () => flag = true);
                                    }
                                })
                        }
                    })
                    .catch((error) => {
                        flag = false;
                        console.log(error);
                        // if error try in 60minutes
                        waitMilliseconds(1000 * 60 * 60, () => flag = true);
                    });
            }
        }
    },

    'Twitch': function () {
        const serviceId = 6;
    }
};

function writeResultToDB(channelsWithFollowers) {

    return new Promise(function(resolve, reject) {

        if (channelsWithFollowers.length) {
            // write followers to DB
            resolve(true);
        } else {
            resolve(false)
        }
    })
}

function waitMilliseconds(milliseconds, callbackForFlagChange) {
    setTimeout(callbackForFlagChange, milliseconds);
}

function parseYouTubeChannels(channels, callbackForFlagChange) {

    return new Promise(function (resolve, reject) {

        var index = 0;
        var iterations = channels.length;
        var channelsWithFollowers = [];

        function next() {
            if (index < iterations) {
                index++;
                getFollowers(channels[index], function (err, result) {
                    if (err) {
                        result.push({
                            'channel': channels[index],
                            'followers': null
                        })
                    } else {
                        result.push({
                            'channel': channels[index],
                            'followers': result
                        })
                    }
                    next();
                });
            } else {
                resolve(channelsWithFollowers);
            }
        }
    });
}

function getOldestChangedChannel(serviceId, callback) {
    //'SELECT * FROM user_stream_settings WHERE service_id = serviceId ORDER BY
    // `last_change_followers_count` ASC LIMIT 1'
    callback(null, {'last_change_followers_count': 123123123123})
}

function getPlatfromChannelsForParsing(platformId, callback) {

    return new Promise(function (resolve, reject) {

        pool.getConnection(function (err, connection) {
            if (err) {
                return reject(err);
            }
            var dayAgo = Date.now() - 1000 * 60 * 60 * 24;
            connection.query('SELECT * FROM user_stream_settings WHERE service_id = ? ' +
                             'AND `last_change_followers_count` > ? ASC LIMIT ?', [
                platformId,
                dayAgo,
                channelsLimit
            ], function (err, channelsForParsing) {
                connection.release();
                if (err) {
                    reject(err);
                }
                resolve(channelsForParsing);
            });
        });
    });
}

for (let platform in platformFollowersParsers) {
    platformFollowersParsers[platform]();
}