
/**
 * Represents a window in a possible chain of iframes
 */
export interface IWindowChainElement {
	/**
	 * The window object for it
	 */
	window: Window;
	/**
	 * The iframe element inside the window.parent corresponding to window
	 */
	iframeElement: Element | null;
}

let hasDifferentOriginAncestorFlag: boolean = false;
let sameOriginWindowChainCache: IWindowChainElement[] | null = null;

function getParentWindowIfSameOrigin(w: Window): Window | null {
	if (!w.parent || w.parent === w) {
		return null;
	}

	// Cannot really tell if we have access to the parent window unless we try to access something in it
	try {
		let location = w.location;
		let parentLocation = w.parent.location;
		if (location.origin !== 'null' && parentLocation.origin !== 'null' && location.origin !== parentLocation.origin) {
			hasDifferentOriginAncestorFlag = true;
			return null;
		}
	} catch (e) {
		hasDifferentOriginAncestorFlag = true;
		return null;
	}

	return w.parent;
}

export class IframeUtils {

	/**
	 * Returns a chain of embedded windows with the same origin (which can be accessed programmatically).
	 * Having a chain of length 1 might mean that the current execution environment is running outside of an iframe or inside an iframe embedded in a window with a different origin.
	 * To distinguish if at one point the current execution environment is running inside a window with a different origin, see hasDifferentOriginAncestor()
	 */
	public static getSameOriginWindowChain(): IWindowChainElement[] {
		if (!sameOriginWindowChainCache) {
			sameOriginWindowChainCache = [];
			let w: Window | null = window;
			let parent: Window | null;
			do {
				parent = getParentWindowIfSameOrigin(w);
				if (parent) {
					sameOriginWindowChainCache.push({
						window: w,
						iframeElement: w.frameElement || null
					});
				} else {
					sameOriginWindowChainCache.push({
						window: w,
						iframeElement: null
					});
				}
				w = parent;
			} while (w);
		}
		return sameOriginWindowChainCache.slice(0);
	}

	/**
	 * Returns true if the current execution environment is chained in a list of iframes which at one point ends in a window with a different origin.
	 * Returns false if the current execution environment is not running inside an iframe or if the entire chain of iframes have the same origin.
	 */
	public static hasDifferentOriginAncestor(): boolean {
		if (!sameOriginWindowChainCache) {
			this.getSameOriginWindowChain();
		}
		return hasDifferentOriginAncestorFlag;
	}

	/**
	 * Returns the position of `childWindow` relative to `ancestorWindow`
	 */
	public static getPositionOfChildWindowRelativeToAncestorWindow(childWindow: Window, ancestorWindow: Window | null) {

		if (!ancestorWindow || childWindow === ancestorWindow) {
			return {
				top: 0,
				left: 0
			};
		}

		let top = 0, left = 0;

		let windowChain = this.getSameOriginWindowChain();

		for (const windowChainEl of windowChain) {

			top += windowChainEl.window.scrollY;
			left += windowChainEl.window.scrollX;

			if (windowChainEl.window === ancestorWindow) {
				break;
			}

			if (!windowChainEl.iframeElement) {
				break;
			}

			let boundingRect = windowChainEl.iframeElement.getBoundingClientRect();
			top += boundingRect.top;
			left += boundingRect.left;
		}

		return {
			top: top,
			left: left
		};
	}
}
