/**
 * Fixed-capacity circular buffer. When full, new items overwrite the oldest.
 */
export class RingBuffer<T> {
  private buffer: Array<T | undefined>;
  private head = 0;   // next write position
  private count = 0;
  private readonly capacity: number;

  constructor(capacity: number) {
    this.capacity = capacity;
    this.buffer = new Array<T | undefined>(capacity);
  }

  push(item: T): void {
    this.buffer[this.head] = item;
    this.head = (this.head + 1) % this.capacity;
    if (this.count < this.capacity) {
      this.count++;
    }
  }

  get size(): number {
    return this.count;
  }

  /** Returns entries oldest-first */
  toArray(): T[] {
    if (this.count === 0) return [];
    const result: T[] = [];
    const start = this.count < this.capacity ? 0 : this.head;
    for (let i = 0; i < this.count; i++) {
      const idx = (start + i) % this.capacity;
      result.push(this.buffer[idx] as T);
    }
    return result;
  }

  clear(): void {
    this.buffer = new Array<T | undefined>(this.capacity);
    this.head = 0;
    this.count = 0;
  }
}