/**
 * @license
 * Copyright 2022 Google Inc.
 * SPDX-License-Identifier: Apache-2.0
 */

import {assert} from '../util/assert.js';
import {Deferred} from '../util/Deferred.js';

/**
 * @internal
 */
export interface Poller<T> {
  start(): Promise<void>;
  stop(): Promise<void>;
  result(): Promise<T>;
}

const MUTATION_OBSERVER_OPTIONS: MutationObserverInit = {
  childList: true,
  subtree: true,
  attributes: true,
};

function canHostShadowRoots(node: Node): boolean {
  return (
    node.nodeType === Node.ELEMENT_NODE ||
    node.nodeType === Node.DOCUMENT_FRAGMENT_NODE
  );
}

/**
 * A shadow root has no parent, so the walk up continues through its host to
 * stay inside the tree the node was added to.
 */
function parentOf(node: Node): Node | null {
  return node.parentNode ?? (node as ShadowRoot).host ?? null;
}

function hasAncestorIn(node: Node, nodes: Set<Node>): boolean {
  let current = node;
  let parent: Node | null;
  while ((parent = parentOf(current))) {
    if (nodes.has(parent)) {
      return true;
    }
    current = parent;
  }
  return false;
}

/**
 * @internal
 */
export class MutationPoller<T> implements Poller<T> {
  #fn: () => Promise<T>;

  #root: Node;

  #observer?: MutationObserver;
  #observedRoots = new WeakSet<Node>();
  #deferred?: Deferred<T>;
  constructor(fn: () => Promise<T>, root: Node) {
    this.#fn = fn;
    this.#root = root;
  }

  async start(): Promise<void> {
    const deferred = (this.#deferred = Deferred.create<T>());
    const result = await this.#fn();
    if (result) {
      deferred.resolve(result);
      return;
    }

    this.#observedRoots = new WeakSet();
    this.#observer = new MutationObserver(async mutations => {
      this.#observeAddedShadowRoots(mutations);
      const result = await this.#fn();
      if (!result) {
        return;
      }
      deferred.resolve(result);
      await this.stop();
    });
    this.#observe(this.#root);
  }

  /**
   * A `subtree` observation does not cross shadow boundaries, so every shadow
   * root needs to be observed on its own.
   */
  #observe(root: Node): void {
    if (!this.#observer || this.#observedRoots.has(root)) {
      return;
    }
    this.#observedRoots.add(root);
    this.#observer.observe(root, MUTATION_OBSERVER_OPTIONS);
    this.#observeShadowRoots(root);
  }

  /**
   * A batch can report a subtree and nodes inside it, so the added nodes are
   * pruned to the top-most ones and each tree is walked once.
   */
  #observeAddedShadowRoots(mutations: MutationRecord[]): void {
    const addedNodes = new Set<Node>();
    for (const mutation of mutations) {
      for (const node of mutation.addedNodes) {
        if (!canHostShadowRoots(node)) {
          continue;
        }
        addedNodes.add(node);
      }
    }
    for (const node of addedNodes) {
      if (!hasAncestorIn(node, addedNodes)) {
        this.#observeShadowRoots(node);
      }
    }
  }

  /**
   * Attaching a shadow root does not emit a mutation, so shadow roots are
   * instead picked up from the trees they arrive in.
   */
  #observeShadowRoots(root: Node): void {
    const walker = document.createTreeWalker(root, NodeFilter.SHOW_ELEMENT);
    do {
      const {shadowRoot} = walker.currentNode as Element;
      if (shadowRoot) {
        this.#observe(shadowRoot);
      }
    } while (walker.nextNode());
  }

  async stop(): Promise<void> {
    assert(this.#deferred, 'Polling never started.');
    if (!this.#deferred.finished()) {
      this.#deferred.reject(new Error('Polling stopped'));
    }
    if (this.#observer) {
      this.#observer.disconnect();
      this.#observer = undefined;
    }
  }

  result(): Promise<T> {
    assert(this.#deferred, 'Polling never started.');
    return this.#deferred.valueOrThrow();
  }
}

/**
 * @internal
 */
export class RAFPoller<T> implements Poller<T> {
  #fn: () => Promise<T>;
  #deferred?: Deferred<T>;
  constructor(fn: () => Promise<T>) {
    this.#fn = fn;
  }

  async start(): Promise<void> {
    const deferred = (this.#deferred = Deferred.create<T>());
    const result = await this.#fn();
    if (result) {
      deferred.resolve(result);
      return;
    }

    const poll = async () => {
      if (deferred.finished()) {
        return;
      }
      const result = await this.#fn();
      if (!result) {
        window.requestAnimationFrame(poll);
        return;
      }
      deferred.resolve(result);
      await this.stop();
    };
    window.requestAnimationFrame(poll);
  }

  async stop(): Promise<void> {
    assert(this.#deferred, 'Polling never started.');
    if (!this.#deferred.finished()) {
      this.#deferred.reject(new Error('Polling stopped'));
    }
  }

  result(): Promise<T> {
    assert(this.#deferred, 'Polling never started.');
    return this.#deferred.valueOrThrow();
  }
}

/**
 * @internal
 */

export class IntervalPoller<T> implements Poller<T> {
  #fn: () => Promise<T>;
  #ms: number;

  #interval?: NodeJS.Timeout;
  #deferred?: Deferred<T>;
  constructor(fn: () => Promise<T>, ms: number) {
    this.#fn = fn;
    this.#ms = ms;
  }

  async start(): Promise<void> {
    const deferred = (this.#deferred = Deferred.create<T>());
    const result = await this.#fn();
    if (result) {
      deferred.resolve(result);
      return;
    }

    this.#interval = setInterval(async () => {
      const result = await this.#fn();
      if (!result) {
        return;
      }
      deferred.resolve(result);
      await this.stop();
    }, this.#ms);
  }

  async stop(): Promise<void> {
    assert(this.#deferred, 'Polling never started.');
    if (!this.#deferred.finished()) {
      this.#deferred.reject(new Error('Polling stopped'));
    }
    if (this.#interval) {
      clearInterval(this.#interval);
      this.#interval = undefined;
    }
  }

  result(): Promise<T> {
    assert(this.#deferred, 'Polling never started.');
    return this.#deferred.valueOrThrow();
  }
}