share a single timestamp array between all graphData objects

lib/time.js

@@ -4,9 +4,10 @@ class TimeTracker {
   constructor (app) {
     this._app = app
     this._points = []
+    this._historicalTimestamps = []
   }
 
-  newTimestamp () {
+  newPingTimestamp () {
     const timestamp = new Date().getTime()
 
     this._points.push(timestamp)
@@ -15,10 +16,40 @@ class TimeTracker {
       this._points.shift()
     }
 
-    return timestamp
+    // Flag each group as history graph additions each minute
+    // This is sent to the frontend for graph updates
+    const updateHistoryGraph = config.logToDatabase && (!this._lastHistoryGraphUpdate || timestamp - this._lastHistoryGraphUpdate >= 60 * 1000)
+
+    if (updateHistoryGraph) {
+      this._lastHistoryGraphUpdate = timestamp
+
+      // Push into timestamps array to update backend state
+      this._historicalTimestamps.push(timestamp)
+
+      if (this._historicalTimestamps.length > TimeTracker.getMaxGraphDataLength()) {
+        this._historicalTimestamps.shift()
+      }
+    }
+
+    return {
+      timestamp,
+      updateHistoryGraph
+    }
   }
 
-  getPointsSeconds () {
+  loadHistoricalTimestamps (timestamps) {
+    this._historicalTimestamps = timestamps
+  }
+
+  getHistoricalPointsSeconds () {
+    return this._historicalTimestamps.map(value => Math.floor(value / 1000))
+  }
+
+  getHistoricalPointSeconds (index) {
+    return Math.floor(this._historicalTimestamps[index] / 1000)
+  }
+
+  getServerPointsSeconds () {
     return this._points.map(value => Math.floor(value / 1000))
   }