Deploy script (#52)

* No-downtime deploy script
* Easier to use helper for average numbers

packages/common/src/helpers.ts

@@ -35,3 +35,80 @@ export function sleep(time: Milliseconds): Promise<void> {
 export const timestamp = Date.now as () => Timestamp;
 
 export function noop() {}
+
+/**
+ * Keep track of last N numbers pushed onto internal stack.
+ * Provides means to get an average of said numbers.
+ */
+export class NumStats<T extends number> {
+  private readonly stack: Array<T>;
+  private readonly history: number;
+  private index: 0;
+
+  constructor(history: number) {
+    if (history < 1) {
+      throw new Error('Must track at least one number');
+    }
+
+    this.history = history;
+    this.stack = new Array(history);
+  }
+
+  public push(val: T) {
+    this.stack[this.index++ % this.history] = val;
+  }
+
+  /**
+   * Get average value of all values on the stack.
+   *
+   * @return {T} average value
+   */
+  public average(): T {
+    if (this.index === 0) {
+      return 0 as T;
+    }
+
+    const list = this.nonEmpty();
+    let sum = 0;
+
+    for (const n of list as Array<number>) {
+      sum += n;
+    }
+
+    return (sum / list.length) as T;
+  }
+
+  /**
+   * Get average value of all values of the stack after filtering
+   * out a number of highest and lowest values
+   *
+   * @param  {number} extremes number of high/low values to ignore
+   * @return {T}               average value
+   */
+  public averageWithoutExtremes(extremes: number): T {
+    if (this.index === 0) {
+      return 0 as T;
+    }
+
+    const list = this.nonEmpty();
+    const count = list.length - extremes * 2;
+
+    if (count < 1) {
+      // Not enough entries to remove desired number of extremes,
+      // fall back to regular average
+      return this.average();
+    }
+
+    let sum = 0;
+
+    for (const n of list.sort((a, b) => a - b).slice(extremes, -extremes)) {
+      sum += n;
+    }
+
+    return (sum / count) as T;
+  }
+
+  private nonEmpty(): Readonly<Array<number>> {
+    return this.index < this.history ? this.stack.slice(0, this.index) : this.stack;
+  }
+}