var express = require('express');
var router = express.Router();
var mqtt = require('mqtt');
var moment = require('moment');
var fs = require('fs/promises');
var crypto = require('crypto');

var DEFAULT_BRENNDAUER = 300;
var brenndauer = DEFAULT_BRENNDAUER;

var MQTTHOST = process.env.MQTTHOST || 'localhost';
var MQTTPORT = process.env.MQTTPORT || 1883;
var MQTTUSR = process.env.MQTTUSR || '';
var MQTTPWD = process.env.MQTTPWD || '';
var TOPIC = process.env.TOPIC || 'sonoff';
var SWITCH_API_TOKEN = process.env.SWITCH_API_TOKEN || '';

var switchOffTimer;
var state = {
    connect: 'disconnected',
    relais: 'UNKNOWN',
    offtime: undefined,
    lastError: undefined
};

var client = mqtt.connect('mqtt://' + MQTTHOST + ':' + MQTTPORT, {
    username: MQTTUSR,
    password: MQTTPWD
});

console.log('Start: ', moment().format('YYYY-MM-DD HH:mm'));

client.on('connect', function() {
    state.connect = 'connected';
    state.lastError = undefined;
    client.subscribe('stat/' + TOPIC + '/POWER', function(err) {
        if (err) {
            state.lastError = 'subscribe failed: ' + err.message;
        }
    });
});

client.on('reconnect', function() {
    state.connect = 'reconnect';
});

client.on('offline', function() {
    state.connect = 'offline';
});

client.on('error', function(err) {
    state.lastError = err.message;
});

client.on('message', function(_topic, message) {
    state.relais = message.toString();
    if (state.relais === 'OFF') {
        state.offtime = undefined;
    }
});

function getResponse() {
    return {
        connect: state.connect,
        relais: state.relais,
        offtime: state.offtime,
        lastError: state.lastError
    };
}

function doPublish(payload) {
    client.publish('cmnd/' + TOPIC + '/Power', payload, function(err) {
        if (err) {
            state.lastError = err.message;
        }
    });

    if (payload === 'On') {
        clearTimeout(switchOffTimer);
        state.offtime = moment().add(brenndauer, 's').format('HH.mm');
        switchOffTimer = setTimeout(doPublish, brenndauer * 1000, 'Off');
    } else if (payload === 'Off') {
        clearTimeout(switchOffTimer);
        state.offtime = undefined;
    }
}

// Read optional runtime config.
(async function loadConfig() {
    try {
        var json = await fs.readFile('config/config.json', 'utf8');
        var cfg = JSON.parse(json);
        if (cfg.brenndauer !== undefined) {
            brenndauer = Number(cfg.brenndauer) || DEFAULT_BRENNDAUER;
        }
    } catch (err) {
        state.lastError = 'config load failed: ' + err.message;
    }
})();

// Query initial state once at startup.
doPublish('');

function timingSafeEqualString(a, b) {
    var aBuf = Buffer.from(String(a));
    var bBuf = Buffer.from(String(b));
    if (aBuf.length !== bBuf.length) {
        return false;
    }
    return crypto.timingSafeEqual(aBuf, bBuf);
}

function extractRequestToken(req) {
    var authHeader = req.get('authorization') || '';
    if (authHeader.startsWith('Bearer ')) {
        return authHeader.slice(7).trim();
    }

    var apiKeyHeader = req.get('x-api-key');
    if (apiKeyHeader) {
        return apiKeyHeader;
    }

    if (typeof req.query.token === 'string') {
        return req.query.token;
    }

    return '';
}

router.use(function(req, res, next) {
    if (!SWITCH_API_TOKEN) {
        return next();
    }

    var providedToken = extractRequestToken(req);
    if (!providedToken || !timingSafeEqualString(providedToken, SWITCH_API_TOKEN)) {
        return res.status(401).json({ error: 'unauthorized' });
    }

    return next();
});

router.get('/:cmd', function(req, res) {
    var cmd = req.params.cmd;

    if (cmd === 'get_status') {
        doPublish('');
        return res.json(getResponse());
    }

    if (cmd === 'switch_on') {
        doPublish('On');
        return res.json(getResponse());
    }

    if (cmd === 'switch_off') {
        doPublish('Off');
        return res.json(getResponse());
    }

    if (cmd === 'check') {
        return res.json(getResponse());
    }

    return res.status(400).json({ error: 'invalid command' });
});

module.exports = router;