/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
import {SelectionModel} from '@angular/cdk/collections';
import {Observable} from 'rxjs';
import {TreeControl} from './tree-control';

/** Base tree control. It has basic toggle/expand/collapse operations on a single data node. */
export abstract class BaseTreeControl<T> implements TreeControl<T> {

  /** Gets a list of descendent data nodes of a subtree rooted at given data node recursively. */
  abstract getDescendants(dataNode: T): T[];

  /** Expands all data nodes in the tree. */
  abstract expandAll(): void;

  /** Saved data node for `expandAll` action. */
  dataNodes: T[];

  /** A selection model with multi-selection to track expansion status. */
  expansionModel: SelectionModel<T> = new SelectionModel<T>(true);

  /** Get depth of a given data node, return the level number. This is for flat tree node. */
  getLevel: (dataNode: T) => number;

  /**
   * Whether the data node is expandable. Returns true if expandable.
   * This is for flat tree node.
   */
  isExpandable: (dataNode: T) => boolean;

  /** Gets a stream that emits whenever the given data node's children change. */
  getChildren: (dataNode: T) => (Observable<T[]> | T[] | undefined | null);

  /** Toggles one single data node's expanded/collapsed state. */
  toggle(dataNode: T): void {
    this.expansionModel.toggle(dataNode);
  }

  /** Expands one single data node. */
  expand(dataNode: T): void {
    this.expansionModel.select(dataNode);
  }

  /** Collapses one single data node. */
  collapse(dataNode: T): void {
    this.expansionModel.deselect(dataNode);
  }

  /** Whether a given data node is expanded or not. Returns true if the data node is expanded. */
  isExpanded(dataNode: T): boolean {
    return this.expansionModel.isSelected(dataNode);
  }

  /** Toggles a subtree rooted at `node` recursively. */
  toggleDescendants(dataNode: T): void {
    this.expansionModel.isSelected(dataNode)
        ? this.collapseDescendants(dataNode)
        : this.expandDescendants(dataNode);
  }

  /** Collapse all dataNodes in the tree. */
  collapseAll(): void {
    this.expansionModel.clear();
  }

  /** Expands a subtree rooted at given data node recursively. */
  expandDescendants(dataNode: T): void {
    let toBeProcessed = [dataNode];
    toBeProcessed.push(...this.getDescendants(dataNode));
    this.expansionModel.select(...toBeProcessed);
  }

  /** Collapses a subtree rooted at given data node recursively. */
  collapseDescendants(dataNode: T): void {
    let toBeProcessed = [dataNode];
    toBeProcessed.push(...this.getDescendants(dataNode));
    this.expansionModel.deselect(...toBeProcessed);
  }
}