Massage the data going into download graph

app/components/download-graph.js

@@ -20,6 +20,54 @@ export default Ember.Component.extend({
 
         let data = this.get('data');
 
+        let datapoints_count = (data[1] || []).length - 1;
+
+        // "on" is an array of booleans where each
+        // element in the array says whether or not the
+        // corresponding line in the data is being drawn or not.
+        //
+        // Each line starts as not being drawn, and can pick up and
+        // be stopped arbitrarily many times before the graph is complete.
+        let on = [];
+        for (let i = 0; i < datapoints_count; i++) {
+            on.push(false);
+        }
+
+        // Start at 1 because the 0th entry in the array
+        // is an array of version numbers
+        for (let i = 1; i < data.length; i++) {
+            for (let k = 0; k < datapoints_count; k++) {
+                // k + 1 because the first entry in the array is the date
+                let value = data[i][k + 1];
+
+                // If we are "off" and are looking at a zero
+                // replace the data at this point with `null`.
+                //
+                // Null tells google.visualization to stop drawing
+                // the line altogether.
+                if (!on[k] && value === 0) {
+                    data[i][k + 1] = null;
+                }
+                // If we are off and the value is not zero, we
+                // need to turn back on.  (keep the value the same though)
+                else if (!on[k] && value !== 0) {
+                    on[k] = true;
+
+                    // We previously wrote a null into data[i - 1][k + 1],
+                    // so to make the graph look pretty, we'll switch it back
+                    // to the zero that it was before.
+                    if (i > 1) {
+                        data[i - 1][k + 1] = 0;
+                    }
+                }
+                // If we are on and the value is zero, turn off
+                // but keep the zero in the array
+                else if (on[k] && value === 0) {
+                    on[k] = false;
+                }
+            }
+        }
+
         if (!data || !window.google || !window.googleChartsLoaded) {
             this.$().hide();
             return;