/**
 * Preallocated, refcounted frame buffers. Raw 1080p frames are 3 MB; allocating
 * one per frame is ~93 MB/s of external memory per stream and drives GC, so the
 * gate and the source bus recycle buffers once every in-flight write is done.
 */
export class BufferPool {
  private readonly free: Buffer[] = [];
  private readonly refs = new Map<Buffer, number>();
  /** Buffers allocated after construction; stays 0 in steady state. */
  allocs = 0;
  constructor(readonly size: number, prealloc: number) {
    for (let i = 0; i < prealloc; i += 1) this.free.push(Buffer.alloc(size));
  }
  /** The caller owns one reference; `release()` it when done. */
  get(): Buffer {
    let buf = this.free.pop();
    if (!buf) { this.allocs += 1; buf = Buffer.alloc(this.size); }
    this.refs.set(buf, 1);
    return buf;
  }
  retain(buf: Buffer): void { this.refs.set(buf, (this.refs.get(buf) ?? 0) + 1); }
  release(buf: Buffer): void {
    const n = (this.refs.get(buf) ?? 0) - 1;
    if (n > 0) { this.refs.set(buf, n); return; }
    if (n < 0) return; // not pool-owned or already free
    this.refs.delete(buf);
    this.free.push(buf);
  }
}