// Single-writer/single-reader latest-sample mailbox. Header: state, UTF-8 byte length.
// State 0 = empty, 1 = owned by a reader/writer, 2 = complete sample.
// Neither side waits: an unread sample can be replaced, and a busy publication is skipped.
export class SharedProfile {
  constructor(buffer = new SharedArrayBuffer(1024 * 1024)) {
    this.buffer = buffer;
    this.header = new Int32Array(buffer, 0, 2);
    this.bytes = new Uint8Array(buffer, 8);
    this.encoder = new TextEncoder();
    this.decoder = new TextDecoder();
  }

  write(json) {
    const bytes = this.encoder.encode(json);
    if (bytes.length > this.bytes.length) return false;
    const state = Atomics.load(this.header, 0);
    if (
      state === 1 ||
      Atomics.compareExchange(this.header, 0, state, 1) !== state
    )
      return false;
    this.bytes.set(bytes);
    this.header[1] = bytes.length;
    Atomics.store(this.header, 0, 2);
    return true;
  }

  read() {
    if (Atomics.compareExchange(this.header, 0, 2, 1) !== 2) return;
    let bytes;
    try {
      bytes = this.bytes.slice(0, this.header[1]);
    } finally {
      Atomics.store(this.header, 0, 0);
    }
    return JSON.parse(this.decoder.decode(bytes));
  }

  clear() {
    Atomics.compareExchange(this.header, 0, 2, 0);
  }
}