fix #287 by using simple division

src/module/timeLabel.js

@@ -1,4 +1,68 @@
 import moment from 'moment';
+const NUM_OF_PARTS_TO_SPLIT = 6;
+
+/**
+ * 若想要有等差的Y軸刻度，則必須確保index是乘以一個共通的被乘數
+ * 此被乘數就是 stepSize
+ * @param {number} maxTimeInSecond 
+ * @returns {object} {resultStepSize, unitToUse}
+ */
+export const getStepSizeOfYTicks = (maxTimeInSecond) => {
+  const numOfParts = NUM_OF_PARTS_TO_SPLIT;
+  const {unitToUse, timeValue} = getTimeUnitAndValueToUse(maxTimeInSecond);
+  let resultStepSize;
+  resultStepSize = Math.floor(timeValue / numOfParts);
+
+  return {resultStepSize, unitToUse};
+}
+
+/**
+ * Convert second to possibly day or hour or mins.
+ * @param {number} secondToDecide 
+ * @returns {object} {unitToUse, timeValue} where timeValue is measured in unitToUse
+ */
+const getTimeUnitAndValueToUse = (secondToDecide) => {
+  const day = 24 * 60 * 60;
+  const hour = 60 * 60;
+  const minutes = 60;
+  const dd = secondToDecide / day;
+  const hh = (secondToDecide % day) / hour;
+  const mm = (secondToDecide % hour) / minutes;
+
+  if (dd > 0 && dd > 1) {
+    return {
+      unitToUse: "d",
+      timeValue: secondToDecide / day,
+    };
+  } else if (hh > 0 && hh > 1) {
+    return {
+      unitToUse: "h",
+      timeValue: (secondToDecide % day) / hour,
+    };
+  } else if (mm > 0 && mm > 1) {
+    return {
+      unitToUse: "m",
+      timeValue: (secondToDecide % hour) / minutes,
+    };
+  } else {
+    return {
+      unitToUse: "s",
+      timeValue: secondToDecide,
+    }
+  }
+};
+
+/**
+ * For the display of PrimeVue chart.
+ * According to the max time of the data given,
+ * split the Y axis into equal part as ticks.
+ * @param {number} stepSize stepSize of Y axis
+ * @param {number} index index of current visiting tick on Y axis
+ * @param {string} unitToUse time unit to display; "dhms" usually
+ */
+export function getYTicksByIndex(stepSize, index, unitToUse){
+  return `${stepSize * index}${unitToUse}`;
+};
 
 /**
  * 將秒數轉換成帶有時間單位的格式