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

import { ArrayExt } from '@lumino/algorithm';
import {
  DisposableDelegate,
  DisposableSet,
  IDisposable
} from '@lumino/disposable';
import { Message } from '@lumino/messaging';
import { Panel, PanelLayout, Widget } from '@lumino/widgets';
import { IStatusBar } from './tokens';

/**
 * Main status bar object which contains all items.
 */
export class StatusBar extends Widget implements IStatusBar {
  constructor() {
    super();
    this.addClass('jp-StatusBar-Widget');

    const rootLayout = (this.layout = new PanelLayout());

    const leftPanel = (this._leftSide = new Panel());
    const middlePanel = (this._middlePanel = new Panel());
    const rightPanel = (this._rightSide = new Panel());

    leftPanel.addClass('jp-StatusBar-Left');
    middlePanel.addClass('jp-StatusBar-Middle');
    rightPanel.addClass('jp-StatusBar-Right');

    rootLayout.addWidget(leftPanel);
    rootLayout.addWidget(middlePanel);
    rootLayout.addWidget(rightPanel);
  }

  /**
   * Register a new status item.
   *
   * @param id - a unique id for the status item.
   *
   * @param statusItem - The item to add to the status bar.
   */
  registerStatusItem(id: string, statusItem: IStatusBar.IItem): IDisposable {
    if (id in this._statusItems) {
      throw new Error(`Status item ${id} already registered.`);
    }

    // Populate defaults for the optional properties of the status item.
    const fullStatusItem = {
      ...Private.statusItemDefaults,
      ...statusItem
    } as Private.IFullItem;
    const { align, item, rank } = fullStatusItem;

    // Connect the activeStateChanged signal to refreshing the status item,
    // if the signal was provided.
    const onActiveStateChanged = () => {
      this._refreshItem(id);
    };
    if (fullStatusItem.activeStateChanged) {
      fullStatusItem.activeStateChanged.connect(onActiveStateChanged);
    }

    const rankItem = { id, rank };

    fullStatusItem.item.addClass('jp-StatusBar-Item');
    this._statusItems[id] = fullStatusItem;

    if (align === 'left') {
      const insertIndex = this._findInsertIndex(this._leftRankItems, rankItem);
      if (insertIndex === -1) {
        this._leftSide.addWidget(item);
        this._leftRankItems.push(rankItem);
      } else {
        ArrayExt.insert(this._leftRankItems, insertIndex, rankItem);
        this._leftSide.insertWidget(insertIndex, item);
      }
    } else if (align === 'right') {
      const insertIndex = this._findInsertIndex(this._rightRankItems, rankItem);
      if (insertIndex === -1) {
        this._rightSide.addWidget(item);
        this._rightRankItems.push(rankItem);
      } else {
        ArrayExt.insert(this._rightRankItems, insertIndex, rankItem);
        this._rightSide.insertWidget(insertIndex, item);
      }
    } else {
      this._middlePanel.addWidget(item);
    }
    this._refreshItem(id); // Initially refresh the status item.

    const disposable = new DisposableDelegate(() => {
      delete this._statusItems[id];
      if (fullStatusItem.activeStateChanged) {
        fullStatusItem.activeStateChanged.disconnect(onActiveStateChanged);
      }
      item.parent = null;
      item.dispose();
    });
    this._disposables.add(disposable);
    return disposable;
  }

  /**
   * Dispose of the status bar.
   */
  dispose(): void {
    this._leftRankItems.length = 0;
    this._rightRankItems.length = 0;
    this._disposables.dispose();
    super.dispose();
  }

  /**
   * Handle an 'update-request' message to the status bar.
   */
  protected onUpdateRequest(msg: Message): void {
    this._refreshAll();
    super.onUpdateRequest(msg);
  }

  private _findInsertIndex(
    side: Private.IRankItem[],
    newItem: Private.IRankItem
  ): number {
    return ArrayExt.findFirstIndex(side, item => item.rank > newItem.rank);
  }

  private _refreshItem(id: string) {
    const statusItem = this._statusItems[id];
    if (statusItem.isActive()) {
      statusItem.item.show();
      statusItem.item.update();
    } else {
      statusItem.item.hide();
    }
  }

  private _refreshAll(): void {
    Object.keys(this._statusItems).forEach(id => {
      this._refreshItem(id);
    });
  }

  private _leftRankItems: Private.IRankItem[] = [];
  private _rightRankItems: Private.IRankItem[] = [];
  private _statusItems: { [id: string]: Private.IFullItem } = {};
  private _disposables = new DisposableSet();
  private _leftSide: Panel;
  private _middlePanel: Panel;
  private _rightSide: Panel;
}

/**
 * A namespace for private functionality.
 */
namespace Private {
  type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
  /**
   * Default options for a status item, less the item itself.
   */
  export const statusItemDefaults: Omit<IStatusBar.IItem, 'item'> = {
    align: 'left',
    rank: 0,
    isActive: () => true,
    activeStateChanged: undefined
  };

  /**
   * An interface for storing the rank of a status item.
   */
  export interface IRankItem {
    id: string;
    rank: number;
  }

  export type DefaultKeys = 'align' | 'rank' | 'isActive';

  /**
   * Type of statusbar item with defaults filled in.
   */
  export type IFullItem = Required<Pick<IStatusBar.IItem, DefaultKeys>> &
    Omit<IStatusBar.IItem, DefaultKeys>;
}
