/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import * as dom from '../Dom';
import { FastDomNode } from './fastDomNode';
import { IMouseEvent, IMouseWheelEvent, StandardWheelEvent } from './mouseEvent';
import { IScrollbarHost } from './abstractScrollbar';
import { HorizontalScrollbar } from './horizontalScrollbar';
import { IScrollableElementChangeOptions, IScrollableElementCreationOptions, IScrollableElementResolvedOptions } from './scrollableElementOptions';
import { VerticalScrollbar } from './verticalScrollbar';
import { Widget } from './widget';
import { TimeoutTimer } from '../../common/Async';
import { Emitter, IEvent } from '../../common/Event';
import { IDisposable, dispose } from '../../common/Lifecycle';
import * as platform from '../../common/Platform';
import { INewScrollDimensions, INewScrollPosition, IScrollDimensions, IScrollPosition, IScrollEvent, Scrollable, ScrollbarVisibility } from './scrollable';
// import 'vs/css!./media/scrollbars';

const enum Constants {
  HIDE_TIMEOUT = 500,
  SCROLL_WHEEL_SENSITIVITY = 50
}

class MouseWheelClassifierItem {
  public timestamp: number;
  public deltaX: number;
  public deltaY: number;
  public score: number;

  constructor(timestamp: number, deltaX: number, deltaY: number) {
    this.timestamp = timestamp;
    this.deltaX = deltaX;
    this.deltaY = deltaY;
    this.score = 0;
  }
}

class MouseWheelClassifier {

  public static readonly INSTANCE = new MouseWheelClassifier();

  private readonly _capacity: number;
  private _memory: MouseWheelClassifierItem[];
  private _front: number;
  private _rear: number;

  constructor() {
    this._capacity = 5;
    this._memory = [];
    this._front = -1;
    this._rear = -1;
  }

  public isPhysicalMouseWheel(): boolean {
    if (this._front === -1 && this._rear === -1) {
      return false;
    }

    let remainingInfluence = 1;
    let score = 0;
    let iteration = 1;

    let index = this._rear;
    while (index !== -1) {
      const influence = (index === this._front ? remainingInfluence : Math.pow(2, -iteration));
      remainingInfluence -= influence;
      score += this._memory[index].score * influence;

      if (index === this._front) {
        break;
      }

      index = (this._capacity + index - 1) % this._capacity;
      iteration++;
    }

    return (score <= 0.5);
  }

  public acceptStandardWheelEvent(e: StandardWheelEvent): void {
    if (platform.isChrome) {
      const targetWindow = dom.getWindow(e.browserEvent);
      const pageZoomFactor = platform.getZoomFactor(targetWindow);
      this.accept(Date.now(), e.deltaX * pageZoomFactor, e.deltaY * pageZoomFactor);
    } else {
      this.accept(Date.now(), e.deltaX, e.deltaY);
    }
  }

  public accept(timestamp: number, deltaX: number, deltaY: number): void {
    let previousItem = null;
    const item = new MouseWheelClassifierItem(timestamp, deltaX, deltaY);

    if (this._front === -1 && this._rear === -1) {
      this._memory[0] = item;
      this._front = 0;
      this._rear = 0;
    } else {
      previousItem = this._memory[this._rear];

      this._rear = (this._rear + 1) % this._capacity;
      if (this._rear === this._front) {
        this._front = (this._front + 1) % this._capacity;
      }
      this._memory[this._rear] = item;
    }

    item.score = this._computeScore(item, previousItem);
  }

  private _computeScore(item: MouseWheelClassifierItem, previousItem: MouseWheelClassifierItem | null): number {

    if (Math.abs(item.deltaX) > 0 && Math.abs(item.deltaY) > 0) {
      return 1;
    }

    let score: number = 0.5;

    if (!this._isAlmostInt(item.deltaX) || !this._isAlmostInt(item.deltaY)) {
      score += 0.25;
    }

    if (previousItem) {
      const absDeltaX = Math.abs(item.deltaX);
      const absDeltaY = Math.abs(item.deltaY);

      const absPreviousDeltaX = Math.abs(previousItem.deltaX);
      const absPreviousDeltaY = Math.abs(previousItem.deltaY);

      const minDeltaX = Math.max(Math.min(absDeltaX, absPreviousDeltaX), 1);
      const minDeltaY = Math.max(Math.min(absDeltaY, absPreviousDeltaY), 1);

      const maxDeltaX = Math.max(absDeltaX, absPreviousDeltaX);
      const maxDeltaY = Math.max(absDeltaY, absPreviousDeltaY);

      const isSameModulo = (maxDeltaX % minDeltaX === 0 && maxDeltaY % minDeltaY === 0);
      if (isSameModulo) {
        score -= 0.5;
      }
    }

    return Math.min(Math.max(score, 0), 1);
  }

  private _isAlmostInt(value: number): boolean {
    const delta = Math.abs(Math.round(value) - value);
    return (delta < 0.01);
  }
}

export class SmoothScrollableElement extends Widget {

  private readonly _options: IScrollableElementResolvedOptions;
  protected readonly _scrollable: Scrollable;
  private readonly _verticalScrollbar: VerticalScrollbar;
  private readonly _horizontalScrollbar: HorizontalScrollbar;
  private readonly _domNode: HTMLElement;

  private readonly _leftShadowDomNode: FastDomNode<HTMLElement> | null;
  private readonly _topShadowDomNode: FastDomNode<HTMLElement> | null;
  private readonly _topLeftShadowDomNode: FastDomNode<HTMLElement> | null;

  private readonly _listenOnDomNode: HTMLElement;

  private _mouseWheelToDispose: IDisposable[];

  private _isDragging: boolean;
  private _mouseIsOver: boolean;

  private readonly _hideTimeout: TimeoutTimer;
  private _shouldRender: boolean;

  private _revealOnScroll: boolean;

  private readonly _onScroll = this._register(new Emitter<IScrollEvent>());
  public readonly onScroll: IEvent<IScrollEvent> = this._onScroll.event;

  public get options(): Readonly<IScrollableElementResolvedOptions> {
    return this._options;
  }

  public constructor(element: HTMLElement, options: IScrollableElementCreationOptions, scrollable?: Scrollable) {
    super();
    options = options ?? {};
    let resolvedScrollable: Scrollable;
    const ownsScrollable = !scrollable;
    if (scrollable) {
      resolvedScrollable = scrollable;
    } else {
      options.mouseWheelSmoothScroll = false;
      resolvedScrollable = new Scrollable({
        forceIntegerValues: true,
        smoothScrollDuration: 0,
        scheduleAtNextAnimationFrame: (callback) => dom.scheduleAtNextAnimationFrame(dom.getWindow(element), callback)
      });
    }

    this._options = resolveOptions(options);
    this._scrollable = resolvedScrollable;

    this._register(this._scrollable.onScroll((e) => {
      this._handleScroll(e);
      this._onScroll.fire(e);
    }));
    if (ownsScrollable) {
      this._register(this._scrollable);
    }

    const scrollbarHost: IScrollbarHost = {
      handleMouseWheel: (mouseWheelEvent: StandardWheelEvent) => this._handleMouseWheel(mouseWheelEvent),
      handleDragStart: () => this._handleDragStart(),
      handleDragEnd: () => this._handleDragEnd(),
    };
    this._verticalScrollbar = this._register(new VerticalScrollbar(this._scrollable, this._options, scrollbarHost));
    this._horizontalScrollbar = this._register(new HorizontalScrollbar(this._scrollable, this._options, scrollbarHost));

    this._domNode = document.createElement('div');
    this._domNode.className = 'xterm-scrollable-element ' + this._options.className;
    this._domNode.setAttribute('role', 'presentation');
    this._domNode.style.position = 'relative';
    this._domNode.appendChild(element);
    this._domNode.appendChild(this._horizontalScrollbar.domNode.domNode);
    this._domNode.appendChild(this._verticalScrollbar.domNode.domNode);

    if (this._options.useShadows) {
      this._leftShadowDomNode = new FastDomNode(document.createElement('div'));
      this._leftShadowDomNode.setClassName('xterm-shadow');
      this._domNode.appendChild(this._leftShadowDomNode.domNode);

      this._topShadowDomNode = new FastDomNode(document.createElement('div'));
      this._topShadowDomNode.setClassName('xterm-shadow');
      this._domNode.appendChild(this._topShadowDomNode.domNode);

      this._topLeftShadowDomNode = new FastDomNode(document.createElement('div'));
      this._topLeftShadowDomNode.setClassName('xterm-shadow');
      this._domNode.appendChild(this._topLeftShadowDomNode.domNode);
    } else {
      this._leftShadowDomNode = null;
      this._topShadowDomNode = null;
      this._topLeftShadowDomNode = null;
    }

    this._listenOnDomNode = this._options.listenOnDomNode ?? this._domNode;

    this._mouseWheelToDispose = [];
    this._setListeningToMouseWheel(this._options.handleMouseWheel);

    this._onmouseover(this._listenOnDomNode, (e) => this._handleMouseOver(e));
    this._onmouseleave(this._listenOnDomNode, (e) => this._handleMouseLeave(e));

    this._hideTimeout = this._register(new TimeoutTimer());
    this._isDragging = false;
    this._mouseIsOver = false;

    this._shouldRender = true;

    this._revealOnScroll = true;
  }

  public override dispose(): void {
    this._mouseWheelToDispose = dispose(this._mouseWheelToDispose);
    super.dispose();
  }

  public getDomNode(): HTMLElement {
    return this._domNode;
  }

  public getScrollDimensions(): IScrollDimensions {
    return this._scrollable.getScrollDimensions();
  }

  public setScrollDimensions(dimensions: INewScrollDimensions): void {
    this._scrollable.setScrollDimensions(dimensions, false);
  }

  public setScrollPosition(update: INewScrollPosition & { reuseAnimation?: boolean }): void {
    if (update.reuseAnimation) {
      this._scrollable.setScrollPositionSmooth(update, update.reuseAnimation);
    } else {
      this._scrollable.setScrollPositionNow(update);
    }
  }

  public getScrollPosition(): IScrollPosition {
    return this._scrollable.getCurrentScrollPosition();
  }

  public updateClassName(newClassName: string): void {
    this._options.className = newClassName;
    if (platform.isMac) {
      this._options.className += ' xterm-mac';
    }
    this._domNode.className = 'xterm-scrollable-element ' + this._options.className;
  }

  public updateOptions(newOptions: IScrollableElementChangeOptions): void {
    if (typeof newOptions.handleMouseWheel !== 'undefined') {
      this._options.handleMouseWheel = newOptions.handleMouseWheel;
      this._setListeningToMouseWheel(this._options.handleMouseWheel);
    }
    if (typeof newOptions.mouseWheelScrollSensitivity !== 'undefined') {
      this._options.mouseWheelScrollSensitivity = newOptions.mouseWheelScrollSensitivity;
    }
    if (typeof newOptions.fastScrollSensitivity !== 'undefined') {
      this._options.fastScrollSensitivity = newOptions.fastScrollSensitivity;
    }
    if (typeof newOptions.scrollPredominantAxis !== 'undefined') {
      this._options.scrollPredominantAxis = newOptions.scrollPredominantAxis;
    }
    if (typeof newOptions.horizontal !== 'undefined') {
      this._options.horizontal = newOptions.horizontal;
    }
    if (typeof newOptions.vertical !== 'undefined') {
      this._options.vertical = newOptions.vertical;
    }
    if (typeof newOptions.horizontalHasArrows !== 'undefined') {
      this._options.horizontalHasArrows = newOptions.horizontalHasArrows;
    }
    if (typeof newOptions.verticalHasArrows !== 'undefined') {
      this._options.verticalHasArrows = newOptions.verticalHasArrows;
    }
    if (typeof newOptions.horizontalScrollbarSize !== 'undefined') {
      this._options.horizontalScrollbarSize = newOptions.horizontalScrollbarSize;
    }
    if (typeof newOptions.verticalScrollbarSize !== 'undefined') {
      this._options.verticalScrollbarSize = newOptions.verticalScrollbarSize;
    }
    if (typeof newOptions.scrollByPage !== 'undefined') {
      this._options.scrollByPage = newOptions.scrollByPage;
    }
    this._horizontalScrollbar.updateOptions(this._options);
    this._verticalScrollbar.updateOptions(this._options);

    if (!this._options.lazyRender) {
      this._render();
    }
  }

  public delegateScrollFromMouseWheelEvent(browserEvent: IMouseWheelEvent): void {
    this._handleMouseWheel(new StandardWheelEvent(browserEvent));
  }

  // -------------------- mouse wheel scrolling --------------------

  private _setListeningToMouseWheel(shouldListen: boolean): void {
    const isListening = (this._mouseWheelToDispose.length > 0);

    if (isListening === shouldListen) {
      return;
    }

    this._mouseWheelToDispose = dispose(this._mouseWheelToDispose);

    if (shouldListen) {
      const onMouseWheel = (browserEvent: IMouseWheelEvent): void => {
        this._handleMouseWheel(new StandardWheelEvent(browserEvent));
      };

      this._mouseWheelToDispose.push(dom.addDisposableListener(this._listenOnDomNode, dom.eventType.MOUSE_WHEEL, onMouseWheel, { passive: false }));
    }
  }

  private _handleMouseWheel(e: StandardWheelEvent): void {
    if (e.browserEvent?.defaultPrevented) {
      return;
    }

    const classifier = MouseWheelClassifier.INSTANCE;
    classifier.acceptStandardWheelEvent(e);

    let didScroll = false;

    if (e.deltaY || e.deltaX) {
      let deltaY = e.deltaY * this._options.mouseWheelScrollSensitivity;
      let deltaX = e.deltaX * this._options.mouseWheelScrollSensitivity;

      if (this._options.scrollPredominantAxis) {
        if (this._options.scrollYToX && deltaX + deltaY === 0) {
          deltaX = deltaY = 0;
        } else if (Math.abs(deltaY) >= Math.abs(deltaX)) {
          deltaX = 0;
        } else {
          deltaY = 0;
        }
      }

      if (this._options.flipAxes) {
        [deltaY, deltaX] = [deltaX, deltaY];
      }

      const shiftConvert = !platform.isMac && e.browserEvent && e.browserEvent.shiftKey;
      if ((this._options.scrollYToX || shiftConvert) && !deltaX) {
        deltaX = deltaY;
        deltaY = 0;
      }

      if (e.browserEvent && e.browserEvent.altKey) {
        deltaX = deltaX * this._options.fastScrollSensitivity;
        deltaY = deltaY * this._options.fastScrollSensitivity;
      }

      const futureScrollPosition = this._scrollable.getFutureScrollPosition();

      let desiredScrollPosition: INewScrollPosition = {};
      if (deltaY) {
        const deltaScrollTop = Constants.SCROLL_WHEEL_SENSITIVITY * deltaY;
        const desiredScrollTop = futureScrollPosition.scrollTop - (deltaScrollTop < 0 ? Math.floor(deltaScrollTop) : Math.ceil(deltaScrollTop));
        this._verticalScrollbar.writeScrollPosition(desiredScrollPosition, desiredScrollTop);
      }
      if (deltaX) {
        const deltaScrollLeft = Constants.SCROLL_WHEEL_SENSITIVITY * deltaX;
        const desiredScrollLeft = futureScrollPosition.scrollLeft - (deltaScrollLeft < 0 ? Math.floor(deltaScrollLeft) : Math.ceil(deltaScrollLeft));
        this._horizontalScrollbar.writeScrollPosition(desiredScrollPosition, desiredScrollLeft);
      }

      desiredScrollPosition = this._scrollable.validateScrollPosition(desiredScrollPosition);

      if (futureScrollPosition.scrollLeft !== desiredScrollPosition.scrollLeft || futureScrollPosition.scrollTop !== desiredScrollPosition.scrollTop) {

        const canPerformSmoothScroll = (
          this._options.mouseWheelSmoothScroll
					&& classifier.isPhysicalMouseWheel()
        );

        if (canPerformSmoothScroll) {
          this._scrollable.setScrollPositionSmooth(desiredScrollPosition);
        } else {
          this._scrollable.setScrollPositionNow(desiredScrollPosition);
        }

        didScroll = true;
      }
    }

    let consumeMouseWheel = didScroll;
    if (!consumeMouseWheel && this._options.alwaysConsumeMouseWheel) {
      consumeMouseWheel = true;
    }
    if (!consumeMouseWheel && this._options.consumeMouseWheelIfScrollbarIsNeeded && (this._verticalScrollbar.isNeeded() || this._horizontalScrollbar.isNeeded())) {
      consumeMouseWheel = true;
    }

    if (consumeMouseWheel) {
      e.preventDefault();
      e.stopPropagation();
    }
  }

  private _handleScroll(e: IScrollEvent): void {
    this._shouldRender = this._horizontalScrollbar.handleScroll(e) || this._shouldRender;
    this._shouldRender = this._verticalScrollbar.handleScroll(e) || this._shouldRender;

    if (this._options.useShadows) {
      this._shouldRender = true;
    }

    if (this._revealOnScroll) {
      this._reveal();
    }

    if (!this._options.lazyRender) {
      this._render();
    }
  }

  public renderNow(): void {
    if (!this._options.lazyRender) {
      throw new Error('Please use `lazyRender` together with `renderNow`!');
    }

    this._render();
  }

  private _render(): void {
    if (!this._shouldRender) {
      return;
    }

    this._shouldRender = false;

    this._horizontalScrollbar.render();
    this._verticalScrollbar.render();

    if (this._options.useShadows) {
      const scrollState = this._scrollable.getCurrentScrollPosition();
      const enableTop = scrollState.scrollTop > 0;
      const enableLeft = scrollState.scrollLeft > 0;

      const leftClassName = (enableLeft ? ' xterm-shadow-left' : '');
      const topClassName = (enableTop ? ' xterm-shadow-top' : '');
      const topLeftClassName = (enableLeft || enableTop ? ' xterm-shadow-top-left-corner' : '');
      this._leftShadowDomNode!.setClassName(`xterm-shadow${leftClassName}`);
      this._topShadowDomNode!.setClassName(`xterm-shadow${topClassName}`);
      this._topLeftShadowDomNode!.setClassName(`xterm-shadow${topLeftClassName}${topClassName}${leftClassName}`);
    }
  }

  // -------------------- fade in / fade out --------------------

  private _handleDragStart(): void {
    this._isDragging = true;
    this._reveal();
  }

  private _handleDragEnd(): void {
    this._isDragging = false;
    this._hide();
  }

  private _handleMouseLeave(e: IMouseEvent): void {
    this._mouseIsOver = false;
    this._hide();
  }

  private _handleMouseOver(e: IMouseEvent): void {
    this._mouseIsOver = true;
    this._reveal();
  }

  private _reveal(): void {
    this._verticalScrollbar.beginReveal();
    this._horizontalScrollbar.beginReveal();
    this._scheduleHide();
  }

  private _hide(): void {
    if (!this._mouseIsOver && !this._isDragging) {
      this._verticalScrollbar.beginHide();
      this._horizontalScrollbar.beginHide();
    }
  }

  private _scheduleHide(): void {
    if (!this._mouseIsOver && !this._isDragging) {
      this._hideTimeout.cancelAndSet(() => this._hide(), Constants.HIDE_TIMEOUT);
    }
  }
}

function resolveOptions(opts: IScrollableElementCreationOptions): IScrollableElementResolvedOptions {
  const result: IScrollableElementResolvedOptions = {
    lazyRender: (typeof opts.lazyRender !== 'undefined' ? opts.lazyRender : false),
    className: (typeof opts.className !== 'undefined' ? opts.className : ''),
    useShadows: (typeof opts.useShadows !== 'undefined' ? opts.useShadows : true),
    handleMouseWheel: (typeof opts.handleMouseWheel !== 'undefined' ? opts.handleMouseWheel : true),
    flipAxes: (typeof opts.flipAxes !== 'undefined' ? opts.flipAxes : false),
    consumeMouseWheelIfScrollbarIsNeeded: (typeof opts.consumeMouseWheelIfScrollbarIsNeeded !== 'undefined' ? opts.consumeMouseWheelIfScrollbarIsNeeded : false),
    alwaysConsumeMouseWheel: (typeof opts.alwaysConsumeMouseWheel !== 'undefined' ? opts.alwaysConsumeMouseWheel : false),
    scrollYToX: (typeof opts.scrollYToX !== 'undefined' ? opts.scrollYToX : false),
    mouseWheelScrollSensitivity: (typeof opts.mouseWheelScrollSensitivity !== 'undefined' ? opts.mouseWheelScrollSensitivity : 1),
    fastScrollSensitivity: (typeof opts.fastScrollSensitivity !== 'undefined' ? opts.fastScrollSensitivity : 5),
    scrollPredominantAxis: (typeof opts.scrollPredominantAxis !== 'undefined' ? opts.scrollPredominantAxis : true),
    mouseWheelSmoothScroll: (typeof opts.mouseWheelSmoothScroll !== 'undefined' ? opts.mouseWheelSmoothScroll : true),

    listenOnDomNode: (typeof opts.listenOnDomNode !== 'undefined' ? opts.listenOnDomNode : null),

    horizontal: (typeof opts.horizontal !== 'undefined' ? opts.horizontal : ScrollbarVisibility.AUTO),
    horizontalScrollbarSize: (typeof opts.horizontalScrollbarSize !== 'undefined' ? opts.horizontalScrollbarSize : 10),
    horizontalSliderSize: (typeof opts.horizontalSliderSize !== 'undefined' ? opts.horizontalSliderSize : 0),
    horizontalHasArrows: (typeof opts.horizontalHasArrows !== 'undefined' ? opts.horizontalHasArrows : false),

    vertical: (typeof opts.vertical !== 'undefined' ? opts.vertical : ScrollbarVisibility.AUTO),
    verticalScrollbarSize: (typeof opts.verticalScrollbarSize !== 'undefined' ? opts.verticalScrollbarSize : 10),
    verticalHasArrows: (typeof opts.verticalHasArrows !== 'undefined' ? opts.verticalHasArrows : false),
    verticalSliderSize: (typeof opts.verticalSliderSize !== 'undefined' ? opts.verticalSliderSize : 0),

    scrollByPage: (typeof opts.scrollByPage !== 'undefined' ? opts.scrollByPage : false)
  };

  result.horizontalSliderSize = (typeof opts.horizontalSliderSize !== 'undefined' ? opts.horizontalSliderSize : result.horizontalScrollbarSize);
  result.verticalSliderSize = (typeof opts.verticalSliderSize !== 'undefined' ? opts.verticalSliderSize : result.verticalScrollbarSize);

  if (platform.isMac) {
    result.className += ' xterm-mac';
  }

  return result;
}