CircularBuffer.ts

export class CircularBuffer<T> implements Iterable<T> {
  private start: number = 0;
  private _length: number = 0;
  private array: T[] = [];
  grow(size: number) {
    if (size > this.array.length) {
      size = Math.max(size, this.array.length * 1.5);
      const array = new Array<T>(size | 0);
      for (const x of this) {
        array.push(x);
      }
      this.array = array;
    }
  }
  get(index: number) {
    return this.array[this.offset(index)];
  }
  set(index: number, value: T) {
    this.array[this.offset(index)] = value;
  }
  private offset(index: number) {
    index = (index + this.start) % this.array.length;
    if (index < 0) {
      index += this.array.length;
    }
    return index;
  }
  push(value: T) {
    if (this.start + this.length == this.array.length) {
      this.array.push(value);
    } else {
      this.grow(this.length + 1);
      this.set(this.length, value);
    }
    this._length++;
  }
  pop() {
    let value;
    if (this.start + this.length == this.array.length) {
      value = this.array.pop();
    } else {
      value = this.get(this.length - 1);
      this.set(this.length - 1, undefined as any);
    }
    this._length--;
    return value;
  }
  unshift(value: T) {
    this.grow(this.length + 1);
    this.set(-1, value);
    this.start = this.offset(-1);
  }
  shift() {
    const value = this.get(0);
    this.set(0, undefined as any);
    this.start++;
    return value;
  }
  get length() {
    return this._length;
  }
  *[Symbol.iterator]() {
    for (let i = 0; i < this.length; i++) {
      yield this.get(i);
    }
  }
}