/** Decoder **/
var payloadStr = decodeToString(payload);
var data = JSON.parse(payloadStr);
var deviceName =  data.deviceName;
var deviceType = 'wM-Bus Reader';
var res = _base64ToArrayBuffer(data.data);

if (res.length < 9)
    return null;

var existSerial = ['66413314','65656691','66413313','66413315'];

var serialNumber1 = null;
var serialNumber2 = null;
var serialNumber3 = null;
var serialNumber4 = null;

var serialNumber = GetWMBusSerial(res[1], res[2], res[3], res[4], existSerial);

var dateTime = GetCurrentDateTime();

var waterWMBusValue1 = null;
var waterWMBusValue2 = null;
var waterWMBusValue3 = null;
var waterWMBusValue4 = null;

GetWMBusMeterValue(res[7], res[8], res[9], res[10], serialNumber, existSerial);

var low_bat = GetFlagError(res[0], 1);
var motion_detect = GetFlagError(res[0], 2);
var magnet_detect = GetFlagError(res[0], 3);
var tamper_detect = GetFlagError(res[0], 4);
var power_on = GetFlagError(res[0], 5);
var power_bat = GetFlagError(res[0], 6);
var err_time = GetFlagError(res[0], 7);
var cfg_done = GetFlagError(res[0], 8);

var result = {
   deviceName: deviceName,
   deviceType: deviceType,
   attributes: {
       integrationName: metadata['integrationName'],
   },
   telemetry: {
       REAL_TIME: dateTime,
       SERIAL1: serialNumber1,
       SERIAL2: serialNumber2,
       SERIAL3: serialNumber3,
       SERIAL4: serialNumber4,

       WATER_WMBUS_VALUE1: waterWMBusValue1,
       WATER_WMBUS_VALUE2: waterWMBusValue2,
       WATER_WMBUS_VALUE3: waterWMBusValue3,
       WATER_WMBUS_VALUE4: waterWMBusValue4,

       FLG_LOW_BAT: low_bat,
       FLG_MOTION_DETECT: motion_detect,
       FLG_MAGNET_DETECT: magnet_detect,
       FLG_TAMPER_DETECT: tamper_detect,
       FLG_POWER_ON: power_on,
       FLG_POWER_BAT: power_bat,
       FLG_ERR_TIME: err_time,
       FLG_CFG_DONE: cfg_done
   }
};

/** Helper functions **/

function decodeToString(payload) {
   return String.fromCharCode.apply(String, payload);
}

function decodeToJson(payload) {
   var str = decodeToString(payload);
   return JSON.parse(str);
}

function GetCurrentDateTime(){
    var a = new Date();
    var year = a.getFullYear().toString();
    var month = (a.getMonth()+1).toString();
    if(month.length==1) month="0"+month;
    var date = a.getDate().toString();
    if(date.length==1) date="0"+date;
    var hour = a.getHours().toString();
    if(hour.length==1) hour="0"+hour;
    var min = a.getMinutes().toString();
    if(min.length==1) min="0"+min;
    var sec = a.getSeconds().toString();
    if(sec.length==1) sec="0"+sec;
    return date + '.' + month + '.' + year + ' ' + hour + ':' + min + ':' + sec;
}

function _base64ToArrayBuffer(base64) {
    var binary_string = atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes;
}

function GetWMBusSerial(byte1, byte2, byte3, byte4, arrSerial) {
    var value1 = parseInt(byte1, 10).toString(2);
    while(value1.length<8){value1='0'+value1;}

    var value2 = parseInt(byte2, 10).toString(2);
    while(value2.length<8){value2='0'+value2;}

    var value3 = parseInt(byte3, 10).toString(2);
    while(value3.length<8){value3='0'+value3;}

    var value4 = parseInt(byte4, 10).toString(2);
    while(value4.length<8){value4='0'+value4;}

    var value = value1[4]+value1[5]+value1[6]+value1[7] + value2 + value3 + value4;
    var res = parseInt(value,2).toString();

    for (k = 0; k < arrSerial.length; k++) {
        if (arrSerial[k] == res) {
            if (k % 4 == 0) serialNumber1 = res;
            if (k % 4 == 1) serialNumber2 = res;
            if (k % 4 == 2) serialNumber3 = res;
            if (k % 4 == 3) serialNumber4 = res;
            return res;
        }
    }
    return null;
}

function GetWMBusMeterValue(byte1, byte2, byte3, byte4, realSerialN, arrSerial) {
    var value1 = parseInt(byte1, 10).toString(16);
    while(value1.length<2){value1='0'+value1;}

    var value2 = parseInt(byte2, 10).toString(16);
    while(value2.length<2){value2='0'+value2;}

    var value3 = parseInt(byte3, 10).toString(16);
    while(value3.length<2){value3='0'+value3;}

    var value4 = parseInt(byte4, 10).toString(16);
    while(value4.length<2){value4='0'+value4;}

    var value = value1 + value2 + value3 + value4;
    var res = parseInt(value,16);

    for (k = 0; k < arrSerial.length; k++) {
        if (arrSerial[k] == realSerialN) {
            if (k % 4 == 0) waterWMBusValue1 = res/1000;
            if (k % 4 == 1) waterWMBusValue2 = res/1000;
            if (k % 4 == 2) waterWMBusValue3 = res/1000;
            if (k % 4 == 3) waterWMBusValue4 = res/1000;
            return null;
        }
    }
    return null;
}

function GetFlagError(byte1, num) {
    var value = parseInt(byte1, 10).toString(2);
    while(value.length<8){value='0'+value;}

    if(num==1) return Number(value[7]);
    if(num==2) return Number(value[6]);
    if(num==3) return Number(value[5]);
    if(num==4) return Number(value[4]);
    if(num==5) return Number(value[3]);
    if(num==6) return Number(value[2]);
    if(num==7) return Number(value[1]);
    if(num==8) return Number(value[0]);

    return null;
}

return result;