// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.

/**
 * - create_view and remove_view are default functions called when adding or removing views
 * - create_view takes a model and an index and returns a view or a promise for a view for that model
 * - remove_view takes a view and destroys it (including calling `view.remove()`)
 * - each time the update() function is called with a new list, the create and remove
 *   callbacks will be called in an order so that if you append the views created in the
 *   create callback and remove the views in the remove callback, you will duplicate
 *   the order of the list.
 * - the remove callback defaults to just removing the view (e.g., pass in null for the second parameter)
 * - the context defaults to the created ViewList.  If you pass another context, the create and remove
 *   will be called in that context.
 */
export class ViewList<T> {
  constructor(
    create_view: (model: any, index: any) => T | Promise<T>,
    remove_view: ((view: T) => void) | null,
    context: any
  ) {
    this.initialize(create_view, remove_view, context);
  }

  initialize(
    create_view: (model: any, index: any) => T | Promise<T>,
    remove_view: ((view: T) => void) | null,
    context: any
  ): void {
    this._handler_context = context || this;
    this._models = [];
    this.views = []; // list of promises for views
    this._create_view = create_view;
    this._remove_view =
      remove_view ||
      function (view): void {
        (view as any).remove();
      };
  }

  /**
   * the create_view, remove_view, and context arguments override the defaults
   * specified when the list is created.
   * after this function, the .views attribute is a list of promises for views
   * if you want to perform some action on the list of views, do something like
   * `Promise.all(myviewlist.views).then(function(views) {...});`
   */
  update(
    new_models: any[],
    create_view?: (model: any, index: any) => T | Promise<T>,
    remove_view?: (view: T) => void,
    context?: any
  ): Promise<T[]> {
    const remove = remove_view || this._remove_view;
    const create = create_view || this._create_view;
    context = context || this._handler_context;
    let i = 0;
    // first, skip past the beginning of the lists if they are identical
    for (; i < new_models.length; i++) {
      if (i >= this._models.length || new_models[i] !== this._models[i]) {
        break;
      }
    }
    const first_removed = i;
    // Remove the non-matching items from the old list.
    const removed = this.views.splice(
      first_removed,
      this.views.length - first_removed
    );
    for (let j = 0; j < removed.length; j++) {
      removed[j].then(function (view) {
        remove.call(context, view);
      });
    }

    // Add the rest of the new list items.
    for (; i < new_models.length; i++) {
      this.views.push(Promise.resolve(create.call(context, new_models[i], i)));
    }
    // make a copy of the input array
    this._models = new_models.slice();
    // return a promise that resolves to all of the resolved views
    return Promise.all(this.views);
  }

  /**
   * removes every view in the list; convenience function for `.update([])`
   * that should be faster
   * returns a promise that resolves after this removal is done
   */
  remove(): Promise<void> {
    return Promise.all(this.views).then((views) => {
      views.forEach((value) =>
        this._remove_view.call(this._handler_context, value)
      );
      this.views = [];
      this._models = [];
    });
  }

  /**
   * Dispose this viewlist.
   *
   * A synchronous function which just deletes references to child views. This
   * function does not call .remove() on child views because that is
   * asynchronous. Use this in cases where child views will be removed in
   * another way.
   */
  dispose(): void {
    this.views = null!;
    this._models = null!;
  }

  _handler_context: any;
  _models: any[];
  views: Promise<T>[];
  _create_view: (model: any, index: any) => T | Promise<T>;
  _remove_view: (view: T) => void;
}