import { SharedProfile } from "./profile.js";

const views = Object.freeze({ f32: Float32Array, u32: Uint32Array, i32: Int32Array });

export class SharedRows {
  #view;

  constructor(buffer, descriptor) {
    if (!(buffer instanceof SharedArrayBuffer)) throw new TypeError("ROWS_DESCRIPTOR");
    this.buffer = buffer;
    this.update(descriptor);
  }

  update(descriptor) {
    if (!views[descriptor.format] || descriptor.name !== (this.descriptor?.name ?? descriptor.name))
      throw new TypeError("ROWS_DESCRIPTOR");
    this.descriptor = Object.freeze(descriptor);
    const View = views[descriptor.format];
    this.#view = new View(this.buffer, descriptor.offset, descriptor.bytes / View.BYTES_PER_ELEMENT);
    return this;
  }

  get name() { return this.descriptor.name; }
  get rows() { return this.descriptor.rows; }
  get stride() { return this.descriptor.stride; }
  get format() { return this.descriptor.format; }
  /** One typed view over the whole array; replaced only when the descriptor changes. */
  get view() { return this.#view; }

  row(index) {
    if (!Number.isInteger(index) || index < 0 || index >= this.rows) throw new RangeError("ROW_RANGE");
    const width = this.stride / views[this.format].BYTES_PER_ELEMENT;
    return this.view.subarray(index * width, (index + 1) * width);
  }

  read(index) { return Array.from(this.row(index)); }

  write(index, values) {
    const row = this.row(index);
    if (!values || values.length !== row.length) throw new RangeError("ROW_WIDTH");
    row.set(values);
    return this;
  }

  share() { return { buffer: this.buffer, descriptor: this.descriptor }; }
}

export class YawnCore {
  #worker;
  #buffer;
  #arrays = new Map();
  #pending = new Map();
  #profileListeners = new Set();
  #profile = new SharedProfile();
  #profileTimer;
  #next = 1;
  /** Optional WebGPU features the device has (WebGPU spelling); populated once `ready` resolves. */
  features = new Set();

  constructor(canvas, { arenaBytes = 64 * 1024 * 1024, debug = false, workerFactory } = {}) {
    if (!canvas) throw new TypeError("canvas is required");
    this.#worker = workerFactory?.() ?? new Worker(new URL("./worker.js", import.meta.url), {
      type: "module",
      name: "yawn-core",
    });
    this.#worker.addEventListener("message", ({ data }) => this.#message(data));
    this.#worker.addEventListener("error", () => this.#fail("WORKER_ERROR"));
    this.#worker.addEventListener("messageerror", () => this.#fail("WORKER_ERROR"));
    this.#worker.start?.();
    const offscreen = canvas.transferControlToOffscreen?.() ?? canvas;
    this.ready = this.#request("init", { canvas: offscreen, arenaBytes, profileBuffer: this.#profile.buffer }, [offscreen]).then(async result => {
      this.#buffer = result.buffer;
      this.features = new Set(result.features);
      for (const descriptor of result.rows) this.#arrays.set(
        descriptor.name,
        new SharedRows(this.#buffer, descriptor),
      );
      if (debug) await this.#request("set-profiler", { enabled: true });
    });
  }

  async createRows({ name, rows, stride, format }) {
    await this.ready;
    const result = await this.#request("create-rows", { name, rows, stride, format });
    return this.#adopt(result.rows, result.commit ? [name] : []);
  }

  async createRowsBatch(rows) {
    await this.ready;
    if (!Array.isArray(rows) || !rows.length) throw new TypeError("ROWS");
    const result = await this.#request("create-rows-batch", { rows });
    const arrays = result.rows.map(descriptor => this.#adopt(descriptor));
    this.#commit(result.commit);
    return arrays;
  }

  async deleteRows(name) {
    await this.ready;
    await this.#request("delete-rows", { name });
    this.#arrays.delete(name);
  }

  /** Reserves `count` contiguous rows and resolves with the first row ID. */
  async allocateObject(name, count = 1) {
    await this.ready;
    const { id, rows, commit } = await this.#request("allocate-object", { name, count });
    this.#adopt(rows, commit ? [name] : []);
    return id;
  }

  /**
   * Publishes a descriptor the worker returned. When the rows moved, this thread owns the copy:
   * the old bytes are copied synchronously into the new region and the worker is told to commit
   * before anything else can be requested, so no write to the array is ever lost.
   */
  #adopt(descriptor, commit = []) {
    const current = this.#arrays.get(descriptor.name);
    if (!current) {
      const array = new SharedRows(this.#buffer, descriptor);
      this.#arrays.set(descriptor.name, array);
      return array;
    }
    if (descriptor.offset !== current.descriptor.offset) {
      const { offset, bytes } = current.descriptor;
      new Uint8Array(this.#buffer, descriptor.offset, bytes).set(new Uint8Array(this.#buffer, offset, bytes));
    }
    current.update(descriptor);
    this.#commit(commit);
    return current;
  }

  #commit(names) {
    if (!names.length) return;
    this.#request("commit-rows", { names }).catch(error => this.#fail(error.code));
  }

  async deleteObject(name, id) {
    await this.ready;
    return this.#request("delete-object", { name, id });
  }

  /** Uploads rows `first .. first + count` of `name` to every active GPU buffer bound to that array. */
  async syncRows(name, first, count) {
    await this.ready;
    return this.#request("sync-rows", { name, first, count });
  }

  async compileGraph(serialized) {
    await this.ready;
    return this.#request("compile-graph", { serialized });
  }

  async switchLoadout(id) {
    await this.ready;
    return this.#request("switch-loadout", { id });
  }

  async uploadTexture(name, image, mipLevel = 0) {
    await this.ready;
    if (
      typeof name !== "string" ||
      !(image instanceof ImageBitmap) ||
      !Number.isInteger(mipLevel) ||
      mipLevel < 0
    )
      throw new TypeError("TEXTURE_SOURCE");
    return this.#request(
      "upload-texture",
      { name, image, mipLevel },
      [image],
    );
  }

  async deleteTexture(name) {
    await this.ready;
    return this.#request("delete-texture", { name });
  }

  async play() {
    await this.ready;
    return this.#request("play");
  }

  async pause() {
    await this.ready;
    return this.#request("pause");
  }

  async setFps(fps) {
    await this.ready;
    return this.#request("set-fps", { fps });
  }

  async setProfiler(enabled) {
    await this.ready;
    return this.#request("set-profiler", { enabled: Boolean(enabled) });
  }

  onProfile(listener) {
    if (typeof listener !== "function") throw new TypeError("PROFILE_LISTENER");
    this.#profileListeners.add(listener);
    if (!this.#profileTimer) this.#profileTimer = setInterval(() => {
      const stats = this.#profile.read();
      if (stats) for (const listener of this.#profileListeners) listener(stats);
    }, 100);
    return () => {
      this.#profileListeners.delete(listener);
      if (!this.#profileListeners.size) {
        clearInterval(this.#profileTimer);
        this.#profileTimer = undefined;
      }
    };
  }

  array(name) {
    const array = this.#arrays.get(name);
    if (!array) throw new Error(`UNKNOWN_ARRAY: ${name}`);
    return array;
  }

  #request(type, payload = {}, transfer = []) {
    const request = this.#next++;
    return new Promise((resolve, reject) => {
      this.#pending.set(request, { resolve, reject });
      this.#worker.postMessage({ type, request, ...payload }, transfer);
    });
  }

  #message(message) {
    const pending = this.#pending.get(message?.request);
    if (!pending) return;
    this.#pending.delete(message.request);
    if (message.error) pending.reject(Object.assign(new Error(message.error), { code: message.error }));
    else pending.resolve(message.result);
  }

  #fail(code) {
    for (const { reject } of this.#pending.values()) reject(Object.assign(new Error(code), { code }));
    this.#pending.clear();
  }

  dispose() {
    this.#fail("DISPOSED");
    clearInterval(this.#profileTimer);
    this.#profileListeners.clear();
    this.#worker.terminate();
  }
}