let textArray = [
  ['Information', '信息解釋'],
  ['Input two positive integer numbers and get the result of multiplication of those two numbers.','輸入兩個正整數，得到這兩個數的乘積結果。'],
  ['It will calculate any big numbers and there is no overflow!', '這個計算的結果可以是任何兩個大數的乘積結果，將不會出現溢出！'],
  ['Enter two <b style="font-size: 150%">BIG</b> integer numbers (till your sore fingers)', '輸入兩個<b style="font-size: 150%">大</b>正整數（敲到你手發酸）'],
  ['First number:', '第一個數字：'],
  ['Second number:', '第二個數字：'],
];

let buttonCaption = [
  ['Calculate', '計算'],
  ['Clear', '清除']
  ];

let resultLabels = [
  ['Calculated result:', '計算的結果：'],
  ['Infinity(overflow)','無法確定（溢出）'],
  ['Verified result:', '驗算的結果：']
]
var lanIndex = 0;

function debug(msg) {
  //if (!window.console) {
    console.log(msg);
  //}
}

function onSelect(elm) {
  lanIndex = elm.value;
  for (var i = 0; i < textArray.length; i++) {
    var e = document.getElementById(i + '');
    e.innerHTML = textArray[i][lanIndex];
  }
  for (var i = 0; i < buttonCaption.length; i++) {
  var e = document.getElementById(i + 'b');
    e.setAttribute('value', buttonCaption[i][lanIndex]);
  }
}

function addCommas(nStr) {
  nStr += "";
  x = nStr.split(".");
  x1 = x[0];
  x2 = x.length > 1 ? "." + x[1] : "";
  var rgx = /(\d+)(\d{3})/;
  while (rgx.test(x1)) {
    x1 = x1.replace(rgx, "$1" + "," + "$2");
  }
  return x1 + x2;
}

function adjustHeight() {
  let list = document.getElementsByTagName("textarea");
  for (let elm of list) {
    var sh = elm.scrollHeight;
    var h = elm.offsetHeight;
    if (h < sh) {
      elm.style.height = sh + "px";
    }
  }
}

function clearResult() {
  let elmID = 'result';
  var elm = document.getElementById(elmID);
  elm.innerHTML = '';
}

function showResult(elmID, text) {
  var fieldNameElement = document.getElementById(elmID);
  if (fieldNameElement) {
    fieldNameElement.innerHTML += text;
  }
}

function v1timesv2(v1, v2) {
  var x = ""; // result
  var i = 0;
  var j = 0;
  var r;
  var r1;
  var r2;
  var k;
  var tempVal;
  var preTempVal = "";
  debug("v1: " + v1);
  debug("v2: " + v2);
  for (
    i = v2.length - 1;
    i >= 0;
    i-- // v2
  ) {
    r2 = 0;
    tempVal = "";
    k = preTempVal.length;
    for (
      j = v1.length - 1;
      j >= 0;
      j-- // v1
    ) {
      if (k-- > 0) {
        r2 += Number(preTempVal[k]);
      }
      r = v1[j] * v2[i] + r2;
      r1 = r % 10;
      r2 = 0;
      if (r > 9) {
        r2 = (r - r1) / 10;
      }
      tempVal = r1 + tempVal;
    }
    if (r > 9) {
      tempVal = r2 + tempVal;
    }
    debug("intermediate calculated result: " + tempVal);
    // Get the last char as result
    x = tempVal[tempVal.length - 1] + x;
    debug("intermediate result: " + x);
    // Get the remaining as previous val
    if (tempVal.length > 1) {
      preTempVal = tempVal.substr(0, tempVal.length - 1);
    } else {
      preTempVal = "";
    }
    debug("== carry forward result: " + preTempVal + " ==");
  }
  x = preTempVal + x;
  debug(">>final result:    " + x);
  debug(
    ">>verified result: " +
      Number(v1) * Number(v2) +
      " (" +
      v1 +
      " x " +
      v2 +
      ")"
  );
  return x;
}

function calculate() {
  var x1 = document.getElementById("v1").value;
  var x2 = document.getElementById("v2").value;
  if (x1 == null || x1 == "" || x2 == null || x2 == "") {
    alert("nubmers must be filled out");
  } else {
    x1 = (x1 + "").replace(/^\s+|\s+$/g, "");
    x2 = (x2 + "").replace(/^\s+|\s+$/g, "");
    var x = v1timesv2(x1, x2);
    const textarea = '<textarea class="result" readonly>';
    const textareaEnd = "</textarea>";
    var i = 0;
    var content = resultLabels[i++][lanIndex] + "<br />" + textarea;
    content += addCommas(x + "");
    content += textareaEnd + "<br />";
    content +=
      textarea +
      "(" +
      x1 +
      " x " +
      x2 +
      ") = \n" +
      x +
      textareaEnd +
      "<br />";
    var x1x2;
    if ((x1 * x2) === Infinity) {
      x1x2 =  resultLabels[i][lanIndex]; 
    } else {
      x1x2 = (x1 * x2) + '';
    }
    i++;
    content +=  resultLabels[i][lanIndex] + "<code>" + x1x2 + "</code></><br /><br />";
    showResult("result", content);
    adjustHeight();
  }
}