import { Directive, Input } from '@angular/core';
import { Utils } from '../utils';

/**
 * Directive to use when a virtual scroller is required
 *
 * @export
 * @class VirtualScrollerDirective
 */
@Directive({
  selector: '[wmVirtualScroller]',
})
export class VirtualScrollerDirective {
  /**
   * Inner variable for totalItems
   *
   * @private
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  private _totalItems = 0;

  /**
   * Inner variable for tolerance
   *
   * @private
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  private _tolerance = 0;

  /**
   * Inner variable for virtualScrollRequired
   *
   * @memberof VirtualScrollerDirective
   */
  virtualScrollRequired = true;

  /**
   * Current scroll value
   *
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  scrollTop = 0;
  /**
   * Enables virtual scrolling functionality on
   * host components.
   *
   * @memberof VirtualScrollerDirective
   */
  @Input()
  virtualScroll = false;

  /**
   * Defines the size of a single item in the list
   *
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  @Input()
  itemHeight = this.viewportHeight / this.pageSize || 20;

  /**
   * Defines the total amount of items in the list
   *
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  @Input()
  get totalItems(): number {
    return this._totalItems;
  }

  /**
   * Defines the total amount of items in the list
   *
   * @memberof VirtualScrollerDirective
   */
  set totalItems(val: number) {
    this._totalItems = val;
  }

  /**
   * Defines the amount of time to retrieve the data after scrolling action
   *
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  @Input()
  scrollDelay: number;

  /**
   * Defines the host component
   *
   * @type {*}
   * @memberof VirtualScrollerDirective
   */
  @Input()
  hostComponent: any;

  /**
   * Defines the amount of displayed items in the list
   * by default the value is 10
   *
   * @memberof VirtualScrollerDirective
   */
  @Input()
  get pageSize() {
    return this.totalItems < 10 ? this.totalItems : 10;
  }

  /**
   * Defines a tolerance of items that are
   * retrieved but not visible in the viewport
   *
   * @memberof VirtualScrollerDirective
   */
  get tolerance(): number {
    return this._tolerance;
  }

  /**
   * Defines a tolerance of items that are
   * retrieved but not visible in the viewport
   *
   * @memberof VirtualScrollerDirective
   */
  set tolerance(val: number) {
    this._tolerance = val;
  }

  /**
   * The initial position of element
   *
   * @memberof VirtualScrollerDirective
   */
  startIndex = 0;

  /**
   * Minimum index value
   *
   * @memberof VirtualScrollerDirective
   */
  minIndex = 0;

  /**
   * Top index scrolling;
   *
   * @memberof VirtualScrollerDirective
   */
  topIndex = 0;

  /**
   * Elements above the viewport
   *
   * @memberof VirtualScrollerDirective
   */
  itemsAbove = this.startIndex - this.tolerance - this.minIndex;

  /**
   * Returns the height of viewport container
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get viewportHeight(): number {
    return this.pageSize * this.itemHeight;
  }

  /**
   * Returns the total height of rendered items in the virtualized container
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get totalHeight(): number {
    return (this.totalItems + 1) * this.itemHeight;
  }

  /**
   * Return the tolerance height
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get toleranceHeight(): number {
    return this.tolerance * this.itemHeight;
  }

  /**
   * Returns the buffer size
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get bufferSize(): number {
    return this.pageSize + 2 * this.tolerance;
  }

  /**
   * Calculates topPaddingHeight
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get topPaddingHeight(): number {
    return this.itemsAbove * this.itemHeight;
  }

  /**
   * Calculates the the bottom padding height value
   *
   * @readonly
   * @type {number}
   * @memberof VirtualScrollerDirective
   */
  get bottomPaddingHeight(): number {
    if (this.itemsAbove >= this.totalItems - this.bufferSize) {
      return 0;
    } else {
      return this.totalHeight - this.topPaddingHeight;
    }
  }

  /**
   * Defines the default value for the scroll delay
   *
   * @return {*}  {number}
   * @memberof VirtualScrollerDirective
   */
  scrollHandlerDelayDefaultValue(): number {
    return Utils.isFirefoxBrowser() ? 300 : 100;
  }

  /**
   * Reset the default indexes values
   *
   * @param {number} totalItems
   * @memberof VirtualScrollerDirective
   */
  resetValues(totalItems: number): void {
    this.startIndex = 0;
    this.minIndex = 0;
    this.totalItems = totalItems;
  }
}