/**
 * @license
 * Copyright Google Inc. 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
 */
/* tslint:disable:array-type member-access variable-name typedef
 only-arrow-functions directive-class-suffix component-class-suffix
 component-selector no-unnecessary-type-assertion arrow-parens
 no-unused-variable*/
import {ElementRef} from '@angular/core';
import {Observable} from 'rxjs/Observable';
import {Subject} from 'rxjs/Subject';

import {Scrollable} from '../scroll/scrollable';

import {ConnectedOverlayPositionChange, ConnectionPositionPair, OriginConnectionPosition, OverlayConnectionPosition, ScrollableViewProperties} from './connected-position';
import {PositionStrategy} from './position-strategy';
import {ViewportRuler} from './viewport-ruler';

/**
 * Container to hold the bounding positions of a particular element with respect
 * to the viewport, where top and bottom are the y-axis coordinates of the
 * bounding rectangle and left and right are the x-axis coordinates.
 */
interface ElementBoundingPositions {
  top: number;
  right: number;
  bottom: number;
  left: number;
}

/**
 * A strategy for positioning overlays. Using this strategy, an overlay is given
 * an implicit position relative some origin element. The relative position is
 * defined in terms of a point on the origin element that is connected to a
 * point on the overlay element. For example, a basic dropdown is connecting the
 * bottom-left corner of the origin to the top-left corner of the overlay.
 */
export class ConnectedPositionStrategy implements PositionStrategy {
  private _dir = 'ltr';

  /** The offset in pixels for the overlay connection point on the x-axis */
  private _offsetX = 0;

  /** The offset in pixels for the overlay connection point on the y-axis */
  private _offsetY = 0;

  /** The Scrollable containers used to check scrollable view properties on
   * position change. */
  private scrollables: Scrollable[] = [];

  /** Whether the we're dealing with an RTL context */
  get _isRtl() {
	return this._dir === 'rtl';
  }

  /** Ordered list of preferred positions, from most to least desirable. */
  _preferredPositions: ConnectionPositionPair[] = [];

  /** The origin element against which the overlay will be positioned. */
  private _origin: HTMLElement;

  /** The overlay pane element. */
  private _pane: HTMLElement;

  /** The last position to have been calculated as the best fit position. */
  private _lastConnectedPosition: ConnectionPositionPair;

  _onPositionChange: Subject<ConnectedOverlayPositionChange> =
		new Subject<ConnectedOverlayPositionChange>();

  /** Emits an event when the connection point changes. */
  get onPositionChange(): Observable<ConnectedOverlayPositionChange> {
	return this._onPositionChange.asObservable();
  }

  constructor(
		private _connectedTo: ElementRef,
		private _originPos: OriginConnectionPosition,
		private _overlayPos: OverlayConnectionPosition,
		private _viewportRuler: ViewportRuler) {
	this._origin = this._connectedTo.nativeElement;
	this.withFallbackPosition(this._originPos, this._overlayPos);
  }

  /** Ordered list of preferred positions, from most to least desirable. */
  get positions() {
	return this._preferredPositions;
  }

  /**
   * To be used to for any cleanup after the element gets destroyed.
   */
  dispose() {
    //
  }

  /**
   * Updates the position of the overlay element, using whichever preferred
   * position relative to the origin fits on-screen.
   * @docs-private
   *
   * @param element Element to which to apply the CSS styles.
   * @returns Resolves when the styles have been applied.
   */
  apply(element: HTMLElement): void {
    // Cache the overlay pane element in case re-calculating position is
    // necessary
	this._pane = element;

    // We need the bounding rects for the origin and the overlay to determine
    // how to position the overlay relative to the origin.
	const originRect = this._origin.getBoundingClientRect();
	const overlayRect = element.getBoundingClientRect();

    // We use the viewport rect to determine whether a position would go
    // off-screen.
	const viewportRect = this._viewportRuler.getViewportRect();

    // Fallback point if none of the fallbacks fit into the viewport.
	let fallbackPoint: OverlayPoint|undefined;
	let fallbackPosition: ConnectionPositionPair|undefined;

    // We want to place the overlay in the first of the preferred positions such
    // that the overlay fits on-screen.
	for (const pos of this._preferredPositions) {
      // Get the (x, y) point of connection on the origin, and then use that to
      // get the (top, left) coordinate for the overlay at `pos`.
		const originPoint = this._getOriginConnectionPoint(originRect, pos);
		const overlayPoint =
			this._getOverlayPoint(originPoint, overlayRect, viewportRect, pos);

      // If the overlay in the calculated position fits on-screen, put it there
      // and we're done.
		if (overlayPoint.fitsInViewport) {
		this._setElementPosition(element, overlayRect, overlayPoint, pos);

        // Save the last connected position in case the position needs to be
        // re-calculated.
		this._lastConnectedPosition = pos;

        // Notify that the position has been changed along with its change
        // properties.
		const scrollableViewProperties =
			this.getScrollableViewProperties(element);
		const positionChange =
			new ConnectedOverlayPositionChange(pos, scrollableViewProperties);
		this._onPositionChange.next(positionChange);

		return;
		} else if (
			!fallbackPoint ||
			fallbackPoint.visibleArea < overlayPoint.visibleArea) {
		fallbackPoint = overlayPoint;
		fallbackPosition = pos;
		}
	}

    // If none of the preferred positions were in the viewport, take the one
    // with the largest visible area.
	this._setElementPosition(
		element, overlayRect, fallbackPoint, fallbackPosition);
  }

  /**
   * This re-aligns the overlay element with the trigger in its last calculated
   * position, even if a position higher in the "preferred positions" list would
   * now fit. This allows one to re-align the panel without changing the
   * orientation of the panel.
   */
  recalculateLastPosition(): void {
	const originRect = this._origin.getBoundingClientRect();
	const overlayRect = this._pane.getBoundingClientRect();
	const viewportRect = this._viewportRuler.getViewportRect();
	const lastPosition =
		this._lastConnectedPosition || this._preferredPositions[0];

	const originPoint =
		this._getOriginConnectionPoint(originRect, lastPosition);
	const overlayPoint = this._getOverlayPoint(
		originPoint, overlayRect, viewportRect, lastPosition);
	this._setElementPosition(
		this._pane, overlayRect, overlayPoint, lastPosition);
  }

  /**
   * Sets the list of Scrollable containers that host the origin element so that
   * on reposition we can evaluate if it or the overlay has been clipped or
   * outside view. Every Scrollable must be an ancestor element of the
   * strategy's origin element.
   */
  withScrollableContainers(scrollables: Scrollable[]) {
	this.scrollables = scrollables;
  }

  /**
   * Adds a new preferred fallback position.
   * @param originPos
   * @param overlayPos
   */
  withFallbackPosition(
		originPos: OriginConnectionPosition,
		overlayPos: OverlayConnectionPosition): this {
	this._preferredPositions.push(
		new ConnectionPositionPair(originPos, overlayPos));
	return this;
  }

  /**
   * Sets the layout direction so the overlay's position can be adjusted to
   * match.
   * @param dir New layout direction.
   */
  withDirection(dir: 'ltr'|'rtl'): this {
	this._dir = dir;
	return this;
  }

  /**
   * Sets an offset for the overlay's connection point on the x-axis
   * @param offset New offset in the X axis.
   */
  withOffsetX(offset: number): this {
	this._offsetX = offset;
	return this;
  }

  /**
   * Sets an offset for the overlay's connection point on the y-axis
   * @param  offset New offset in the Y axis.
   */
  withOffsetY(offset: number): this {
	this._offsetY = offset;
	return this;
  }

  /**
   * Gets the horizontal (x) "start" dimension based on whether the overlay is
   * in an RTL context.
   * @param rect
   */
  private _getStartX(rect: ClientRect): number {
	return this._isRtl ? rect.right : rect.left;
  }

  /**
   * Gets the horizontal (x) "end" dimension based on whether the overlay is in
   * an RTL context.
   * @param rect
   */
  private _getEndX(rect: ClientRect): number {
	return this._isRtl ? rect.left : rect.right;
  }


  /**
   * Gets the (x, y) coordinate of a connection point on the origin based on a
   * relative position.
   * @param originRect
   * @param pos
   */
  private _getOriginConnectionPoint(
		originRect: ClientRect, pos: ConnectionPositionPair): Point {
	const originStartX = this._getStartX(originRect);
	const originEndX = this._getEndX(originRect);

	let x: number;
	if (pos.originX === 'center') {
		x = originStartX + (originRect.width / 2);
	} else {
		x = pos.originX === 'start' ? originStartX : originEndX;
	}

	let y: number;
	if (pos.originY === 'center') {
		y = originRect.top + (originRect.height / 2);
	} else {
		y = pos.originY === 'top' ? originRect.top : originRect.bottom;
	}

	return {x, y};
  }


  /**
   * Gets the (x, y) coordinate of the top-left corner of the overlay given a
   * given position and origin point to which the overlay should be connected,
   * as well as how much of the element would be inside the viewport at that
   * position.
   */
  private _getOverlayPoint(
		originPoint: Point, overlayRect: ClientRect, viewportRect: ClientRect,
		pos: ConnectionPositionPair): OverlayPoint {
    // Calculate the (overlayStartX, overlayStartY), the start of the potential
    // overlay position relative to the origin point.
	let overlayStartX: number;
	if (pos.overlayX === 'center') {
		overlayStartX = -overlayRect.width / 2;
	} else if (pos.overlayX === 'start') {
		overlayStartX = this._isRtl ? -overlayRect.width : 0;
	} else {
		overlayStartX = this._isRtl ? 0 : -overlayRect.width;
	}

	let overlayStartY: number;
	if (pos.overlayY === 'center') {
		overlayStartY = -overlayRect.height / 2;
	} else {
		overlayStartY = pos.overlayY === 'top' ? 0 : -overlayRect.height;
	}

    // The (x, y) coordinates of the overlay.
	const x = originPoint.x + overlayStartX + this._offsetX;
	const y = originPoint.y + overlayStartY + this._offsetY;

    // How much the overlay would overflow at this position, on each side.
	const leftOverflow = 0 - x;
	const rightOverflow = (x + overlayRect.width) - viewportRect.width;
	const topOverflow = 0 - y;
	const bottomOverflow = (y + overlayRect.height) - viewportRect.height;

    // Visible parts of the element on each axis.
	const visibleWidth =
		this._subtractOverflows(overlayRect.width, leftOverflow, rightOverflow);
	const visibleHeight = this._subtractOverflows(
		overlayRect.height, topOverflow, bottomOverflow);

    // The area of the element that's within the viewport.
	const visibleArea = visibleWidth * visibleHeight;
	const fitsInViewport =
		(overlayRect.width * overlayRect.height) === visibleArea;

	return {x, y, fitsInViewport, visibleArea};
  }

  /**
   * Gets the view properties of the trigger and overlay, including whether they
   * are clipped or completely outside the view of any of the strategy's
   * scrollables.
   */
  private getScrollableViewProperties(overlay: HTMLElement):
		ScrollableViewProperties {
	const originBounds = this._getElementBounds(this._origin);
	const overlayBounds = this._getElementBounds(overlay);
	const scrollContainerBounds =
		this.scrollables.map((scrollable: Scrollable) => {
			return this._getElementBounds(
				scrollable.getElementRef().nativeElement);
		});

	return {
		isOriginClipped:
			this.isElementClipped(originBounds, scrollContainerBounds),
		isOriginOutsideView:
			this.isElementOutsideView(originBounds, scrollContainerBounds),
		isOverlayClipped:
			this.isElementClipped(overlayBounds, scrollContainerBounds),
		isOverlayOutsideView:
			this.isElementOutsideView(overlayBounds, scrollContainerBounds),
	};
  }

  /** Whether the element is completely out of the view of any of the
   * containers. */
  private isElementOutsideView(
		elementBounds: ElementBoundingPositions,
		containersBounds: ElementBoundingPositions[]): boolean {
	return containersBounds.some(
		(containerBounds: ElementBoundingPositions) => {
			const outsideAbove = elementBounds.bottom < containerBounds.top;
			const outsideBelow = elementBounds.top > containerBounds.bottom;
			const outsideLeft = elementBounds.right < containerBounds.left;
			const outsideRight = elementBounds.left > containerBounds.right;

			return outsideAbove || outsideBelow || outsideLeft || outsideRight;
		});
  }

  /** Whether the element is clipped by any of the containers. */
  private isElementClipped(
		elementBounds: ElementBoundingPositions,
		containersBounds: ElementBoundingPositions[]): boolean {
	return containersBounds.some(
		(containerBounds: ElementBoundingPositions) => {
			const clippedAbove = elementBounds.top < containerBounds.top;
			const clippedBelow = elementBounds.bottom > containerBounds.bottom;
			const clippedLeft = elementBounds.left < containerBounds.left;
			const clippedRight = elementBounds.right > containerBounds.right;

			return clippedAbove || clippedBelow || clippedLeft || clippedRight;
		});
  }

  /** Physically positions the overlay element to the given coordinate. */
  private _setElementPosition(
		element: HTMLElement, overlayRect: ClientRect, overlayPoint: Point,
		pos: ConnectionPositionPair) {
    // We want to set either `top` or `bottom` based on whether the overlay
    // wants to appear above or below the origin and the direction in which the
    // element will expand.
	const verticalStyleProperty = pos.overlayY === 'bottom' ? 'bottom' : 'top';

    // When using `bottom`, we adjust the y position such that it is the
    // distance from the bottom of the viewport rather than the top.
	const y = verticalStyleProperty === 'top' ?
		overlayPoint.y :
		document.documentElement.clientHeight -
			(overlayPoint.y + overlayRect.height);

    // We want to set either `left` or `right` based on whether the overlay
    // wants to appear "before" or "after" the origin, which determines the
    // direction in which the element will expand. For the horizontal axis, the
    // meaning of "before" and "after" change based on whether the page is in
    // RTL or LTR.
	let horizontalStyleProperty: any;
	if (this._dir === 'rtl') {
		horizontalStyleProperty = pos.overlayX === 'end' ? 'left' : 'right';
	} else {
		horizontalStyleProperty = pos.overlayX === 'end' ? 'right' : 'left';
	}

    // When we're setting `right`, we adjust the x position such that it is the
    // distance from the right edge of the viewport rather than the left edge.
	const x = horizontalStyleProperty === 'left' ?
		overlayPoint.x :
		document.documentElement.clientWidth -
			(overlayPoint.x + overlayRect.width);


    // Reset any existing styles. This is necessary in case the preferred
    // position has changed since the last `apply`.
	['top', 'bottom', 'left', 'right'].forEach(
		(p: any) => element.style[p] = null);

	element.style[verticalStyleProperty] = `${y}px`;
	element.style[horizontalStyleProperty] = `${x}px`;
  }

  /** Returns the bounding positions of the provided element with respect to the
   * viewport. */
  private _getElementBounds(element: HTMLElement): ElementBoundingPositions {
	const boundingClientRect = element.getBoundingClientRect();
	return {
		top: boundingClientRect.top,
		right: boundingClientRect.left + boundingClientRect.width,
		bottom: boundingClientRect.top + boundingClientRect.height,
		left: boundingClientRect.left
	};
  }

  /**
   * Subtracts the amount that an element is overflowing on an axis from it's
   * length.
   */
  private _subtractOverflows(length: number, ...overflows: number[]): number {
	return overflows.reduce((currentValue: number, currentOverflow: number) => {
		return currentValue - Math.max(currentOverflow, 0);
	}, length);
  }
}

/** A simple (x, y) coordinate. */
interface Point {
  x: number;
  y: number;
}

/**
 * Expands the simple (x, y) coordinate by adding info about whether the
 * element would fit inside the viewport at that position, as well as
 * how much of the element would be visible.
 */
interface OverlayPoint extends Point {
  visibleArea: number;
  fitsInViewport: boolean;
}