Add a general, reusable ringbuffer.

helpers/ringbuffer.js

@@ -0,0 +1,30 @@
+export class RingBuffer {
+    constructor(size) {
+        this.size = size;
+        let data = [];
+        for (let i=0; i<size; i++) {
+            data.push([0, 0]);
+        }
+        this.head = 0;
+        this.data = data;
+    }
+
+    push(recent, completed) {
+        this.data[this.head] = [recent, completed];
+        this.head += 1;
+        this.head %= this.size;
+    }
+
+    series() {
+        let result = [[], []];
+        for (let i=this.head; i<this.size; i++) {
+            result[0].push(this.data[i][0]);
+            result[1].push(this.data[i][1]);
+        }
+        for (let i=0; i<this.head; i++) {
+            result[0].push(this.data[i][0]);
+            result[1].push(this.data[i][1]);
+        }
+        return result;
+    }
+}