import type { Loadable } from './loadable.ts';

const SHARED = Symbol.for('moroutine.shared');

/** A fixed-size shared byte buffer backed by SharedArrayBuffer. */
export class Bytes implements Loadable<Readonly<Uint8Array>> {
  readonly size: number;
  readonly view: Uint8Array;

  static byteAlignment = 1;

  constructor(size: number, buffer?: SharedArrayBuffer, byteOffset?: number) {
    this.size = size;
    const buf = buffer ?? new SharedArrayBuffer(size);
    const offset = byteOffset ?? 0;
    this.view = new Uint8Array(buf, offset, size);
  }

  /**
   * Returns a readonly view of the buffer. No copy — mutations via `view` are visible.
   * @returns A readonly typed array view into the shared buffer.
   */
  load(): Readonly<Uint8Array> {
    return this.view as Readonly<Uint8Array>;
  }

  /**
   * Writes data into the buffer. Must be exact length.
   * @param value - A Uint8Array whose length must equal the buffer's size.
   */
  store(value: Uint8Array): void {
    if (value.length !== this.size) {
      throw new RangeError(`Expected Uint8Array of length ${this.size}, got ${value.length}`);
    }
    this.view.set(value);
  }

  [SHARED](): { tag: string; buffer: SharedArrayBuffer; byteOffset: number; size: number } {
    return {
      tag: 'Bytes',
      buffer: this.view.buffer as SharedArrayBuffer,
      byteOffset: this.view.byteOffset,
      size: this.size,
    };
  }
}