/**
 * 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: number[]

  hasFullBuffer(): boolean {
    return this.buffer.length === this.bufferMaxSize
  }

  push(value: number): number {
    let removed = 0
    if (this.hasFullBuffer()) {
      removed = this.buffer.shift() || 0
    }
    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
  }
}