IsOccupied computed based on last readings

UI.Web.Dashboard/src/app/sensors.config.js

 define({
     "Sensor 1": {
        name: "Chill room"
+    },
+
+    __default__: {
+        minReadingsCount: 3,
+        readingExpiry: 3 * 60, //in seconds
+        lastReadings: 10 //number of last readings taken into account when calculating isOccupied
     }
 });
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UI.Web.Dashboard/src/components/sensor/sensorViewModel.js

-define(['knockout', "app/sensors.config", "lodash"], function(ko, sensorsConfig, _) {
+define(['knockout', "app/sensors.config", "lodash"], function (ko, sensorsConfig, _) {
 
   function SensorViewModel(sensorData) {
     this.name = getName(sensorData.id);
     this.readings = ko.observableArray([]);
+    this.config = getConfig(sensorData.id);
 
     this.update(sensorData);
 
-    this.isOccupied = ko.computed(_.bind(function () {
-      var lastReading = _.last(this.readings());
+    this.isOccupied = ko.computed(_.bind(calculateIsOcupied, this));
 
-      if(!lastReading)
+    var clearReadingsPeriodically = _.bind(function () {
+      this.clearExpiredReadings();
+      setTimeout(clearReadingsPeriodically, 10 * 1000);
+    }, this);
+    clearReadingsPeriodically();
+  }
+
+  function calculateIsOcupied() {
+    var readings = this.readings();
+
+    if (readings.length < this.config.minReadingsCount)
       return undefined;
 
-      return lastReading.isOccupied;
+    var lastReadings = _.slice(_.orderBy(readings, "timestamp", "desc"), 0, this.config.lastReadings);
+
+    var occupiedReadingsCount = 0;
+    var notOccupiedReadingsCount = 0;
+
+    _.forEach(lastReadings, function (reading) {
+      if (reading.isOccupied) {
+        occupiedReadingsCount++;
+      } else {
+        notOccupiedReadingsCount++;
+      }
+    });
 
-    }, this));
+    return occupiedReadingsCount > notOccupiedReadingsCount;
   }
 
-  SensorViewModel.prototype.update = function(sensorData){
+  SensorViewModel.prototype.clearExpiredReadings = function () {
+    var currentDate = new Date();
+    var expiryInMiliseconds = this.config.readingExpiry * 1000;
+
+    this.readings.remove(function (reading) {
+      return currentDate - reading.timestamp > expiryInMiliseconds;
+    });
+  };
+
+  SensorViewModel.prototype.update = function (sensorData) {
     this.readings.push(_.pick(sensorData, ["isOccupied", "timestamp"]));
     this.timestamp = ko.observable(sensorData.timestamp);
   };
 
-  function getName(id){
+  function getName(id) {
     return (sensorsConfig[id] && sensorsConfig[id].name) || id;
   }
 
+  function getConfig(id) {
+    return _.merge(sensorsConfig[id] || {}, sensorsConfig.__default__);    
+  }
+
   return SensorViewModel;
 });
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