export function loadTemplate(
  element: ParentNode,
  id: string
): DocumentFragment {
  let template = element.querySelector(`#${id}-template`);
  if (template !== null && template instanceof HTMLTemplateElement) {
    const fragment = document.importNode(template.content, true);
    fragment.querySelectorAll('template').forEach((t) => {
      let parent = t.parentNode!;
      const templateName = t.getAttribute('name');
      if (templateName === null) {
        return;
      }
      let template = loadTemplate(fragment, templateName);
      let firstElement = template.querySelector('*');
      if (firstElement !== null) {
        for (let i = 0; i < t.classList.length; ++i) {
          firstElement.classList.add(t.classList[i]);
        }
      }
      parent.insertBefore(template, t);
      parent.removeChild(t);
    });
    return fragment;
  } else {
    throw new Error(`#${id}-template is not a template`);
  }
}

export function clearChildren(node: Node): void {
  while (node.lastChild !== null) {
    node.removeChild(node.lastChild);
  }
}

export function getElement<E extends HTMLElement>(
  element: ParentNode,
  selector: string
): E {
  const e = element.querySelector(selector);
  if (e === null) {
    throw new Error(`Could not find required element ${selector}`);
  }
  return e as E;
}

export function createElement(
  elementName: string,
  value: string | null
): HTMLElement {
  const e = document.createElement(elementName);
  e.textContent = value;
  return e;
}

export function loadBackground(url: string): Promise<void> {
  if (url.includes('.')) {
    return new Promise((resolve, reject) => {
      let image = new Image();
      image.onload = (event) => resolve();
      image.src = url;
    });
  } else {
    return Promise.resolve();
  }
}

class ListenerManager {
  constructor(
    private target: EventTarget,
    private event: string,
    private handler: EventListener
  ) {}

  attach(): void {
    this.target.addEventListener(this.event, this.handler);
  }

  detach(): void {
    this.target.removeEventListener(this.event, this.handler);
  }
}

export class ListenersManager {
  private listeners: ListenerManager[] = [];

  add(
    target: EventTarget,
    event: string,
    handler: EventListener,
    attach: boolean = true
  ): void {
    let listener = new ListenerManager(target, event, handler);
    this.listeners.push(listener);
    if (attach) {
      listener.attach();
    }
  }

  attach(): void {
    this.listeners.forEach((l) => l.attach());
  }

  detach(): void {
    this.listeners.forEach((l) => l.detach());
  }
}

export class FnContext {
  current: Symbol = Symbol();

  invalidate() {
    this.current = Symbol();
  }

  wrap<T extends Function>(fn: T): T {
    const id = this.current;
    const wrappedFn = (...args: any[]) => {
      if (this.current === id) {
        return fn(...args);
      }
    };
    return (wrappedFn as any) as T;
  }
}

export interface Deferred {
  promise: Promise<void>;
  resolve: () => void;
}

export function makeDeferred(): Deferred {
  let resolve: undefined | (() => void);
  const promise = new Promise<void>((r) => {
    resolve = r;
  });
  return {
    promise,
    resolve: resolve!,
  };
}

export function deepEqual(
  a: unknown,
  b: unknown,
  context: string = ''
): [boolean, string] {
  if (a === b) {
    return [true, context];
  }
  if (a === null || b === null || a === undefined || b === undefined) {
    return [false, context];
  }
  if (typeof a !== typeof b) {
    return [false, context];
  }
  if (Array.isArray(a) && Array.isArray(b)) {
    if (a.length !== b.length) {
      return [false, context];
    }
    for (let i = 0; i < a.length; ++i) {
      const result = deepEqual(a[i], b[i], `${context}/${i}`);
      if (!result[0]) {
        return result;
      }
    }
    return [true, context];
  }
  if (typeof a === 'object' && typeof b === 'object') {
    const keys = Object.keys(a!);
    for (const key of keys) {
      // @ts-ignore
      const result = deepEqual(a[key], b[key], `${context}/${key}`);
      if (!result[0]) {
        return result;
      }
    }
    for (const key of Object.keys(b!)) {
      if (!keys.includes(key)) {
        return [false, `${context}/${key}`];
      }
    }
    return [true, context];
  }
  return [a === b, context];
}