Add rate() function resistant to counter reset

dist/datasource-zabbix/timeseries.js

@@ -154,6 +154,10 @@ System.register(['lodash', './utils'], function (_export, _context) {
     });
   }
 
+  /**
+   * Simple delta. Calculate value delta between points.
+   * @param {*} datapoints
+   */
   function delta(datapoints) {
     var newSeries = [];
     var deltaValue = void 0;
@@ -164,6 +168,33 @@ System.register(['lodash', './utils'], function (_export, _context) {
     return newSeries;
   }
 
+  /**
+   * Calculates rate per second. Resistant to counter reset.
+   * @param {*} datapoints
+   */
+  function rate(datapoints) {
+    var newSeries = [];
+    var point = void 0,
+        point_prev = void 0;
+    var valueDelta = 0;
+    var timeDelta = 0;
+    for (var i = 1; i < datapoints.length; i++) {
+      point = datapoints[i];
+      point_prev = datapoints[i - 1];
+
+      // Convert ms to seconds
+      timeDelta = (point[POINT_TIMESTAMP] - point_prev[POINT_TIMESTAMP]) / 1000;
+
+      // Handle counter reset - use previous value
+      if (point[POINT_VALUE] >= point_prev[POINT_VALUE]) {
+        valueDelta = (point[POINT_VALUE] - point_prev[POINT_VALUE]) / timeDelta;
+      }
+
+      newSeries.push([valueDelta, point[POINT_TIMESTAMP]]);
+    }
+    return newSeries;
+  }
+
   function SUM(values) {
     var sum = 0;
     _.each(values, function (value) {
@@ -292,6 +323,7 @@ System.register(['lodash', './utils'], function (_export, _context) {
         sumSeries: sumSeries,
         scale: scale,
         delta: delta,
+        rate: rate,
         SUM: SUM,
         COUNT: COUNT,
         AVERAGE: AVERAGE,