Migrate LowPassFilter

Summary: _typescript_

Reviewed By: danielbuechele

Differential Revision: D16764120

fbshipit-source-id: 03185c74f3a1e753089ea550d3f193027aae9424

src/utils/LowPassFilter.tsx

@@ -0,0 +1,51 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+export default class LowPassFilter {
+  constructor(smoothing: number = 0.9) {
+    this.smoothing = smoothing;
+    this.buffer = [];
+    this.bufferMaxSize = 5;
+  }
+
+  bufferMaxSize: number;
+  smoothing: number;
+  buffer: Array<number>;
+
+  hasFullBuffer(): boolean {
+    return this.buffer.length === this.bufferMaxSize;
+  }
+
+  push(value: number): number {
+    let removed: number = 0;
+
+    if (this.hasFullBuffer()) {
+      removed = this.buffer.shift();
+    }
+
+    this.buffer.push(value);
+
+    return removed;
+  }
+
+  next(nextValue: number): number {
+    // push new value to the end, and remove oldest one
+    const removed = this.push(nextValue);
+
+    // smooth value using all values from buffer
+    const result = this.buffer.reduce(this._nextReduce, removed);
+
+    // replace smoothed value
+    this.buffer[this.buffer.length - 1] = result;
+
+    return result;
+  }
+
+  _nextReduce = (last: number, current: number): number => {
+    return this.smoothing * current + (1 - this.smoothing) * last;
+  };
+}