implement new way of measuring stats that allows arbitrary timeranges

htdocs/lib/Measurement.js

@@ -0,0 +1,62 @@
+function Measurement() {
+    this.reset();
+};
+
+Measurement.prototype.add = function(v) {
+    this.value += v;
+};
+
+Measurement.prototype.getValue = function() {
+    return this.value;
+};
+
+Measurement.prototype.getElapsed = function() {
+    return new Date() - this.start;
+};
+
+Measurement.prototype.getRate = function() {
+    return this.getValue() / this.getElapsed();
+};
+
+Measurement.prototype.reset = function() {
+    this.value = 0;
+    this.start = new Date();
+};
+
+Measurement.prototype.report = function(range, interval, callback) {
+    return new Reporter(this, range, interval, callback);
+}
+
+function Reporter(measurement, range, interval, callback) {
+    this.measurement = measurement;
+    this.range = range;
+    this.samples = [];
+    this.callback = callback;
+    this.interval = setInterval(this.report.bind(this), interval);
+};
+
+Reporter.prototype.sample = function(){
+    this.samples.push({
+        timestamp: new Date(),
+        value: this.measurement.getValue()
+    });
+};
+
+Reporter.prototype.report = function(){
+    this.sample();
+    var now = new Date();
+    var minDate = now.getTime() - this.range;
+    this.samples = this.samples.filter(function(s) {
+        return s.timestamp.getTime() > minDate;
+    });
+    this.samples.sort(function(a, b) {
+        return a.timestamp - b.timestamp;
+    });
+    var oldest = this.samples[0];
+    var newest = this.samples[this.samples.length -1];
+    var elapsed = newest.timestamp - oldest.timestamp;
+    if (elapsed <= 0) return;
+    var accumulated = newest.value - oldest.value;
+    // we want rate per second, but our time is in milliseconds... compensate by 1000
+    this.callback(accumulated * 1000 / elapsed);
+};