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

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

const sameOriginWindowChainCache = new WeakMap<Window, IWindowChainElement[] | 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 {
    const location = w.location;
    const parentLocation = w.parent.location;
    if (location.origin !== 'null' && parentLocation.origin !== 'null' && location.origin !== parentLocation.origin) {
      return null;
    }
  } catch {
    return null;
  }

  return w.parent;
}

export class IframeUtils {

  /**
   * Returns a chain of embedded windows with the same origin.
   * The chain 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.
   */
  private static _getSameOriginWindowChain(targetWindow: Window): IWindowChainElement[] {
    let windowChainCache = sameOriginWindowChainCache.get(targetWindow);
    if (!windowChainCache) {
      windowChainCache = [];
      sameOriginWindowChainCache.set(targetWindow, windowChainCache);
      let w: Window | null = targetWindow;
      let parent: Window | null;
      do {
        parent = getParentWindowIfSameOrigin(w);
        if (parent) {
          windowChainCache.push({
            window: new WeakRef(w),
            iframeElement: w.frameElement ?? null
          });
        } else {
          windowChainCache.push({
            window: new WeakRef(w),
            iframeElement: null
          });
        }
        w = parent;
      } while (w);
    }
    return windowChainCache.slice(0);
  }

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

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

    let top = 0; let left = 0;

    const windowChain = this._getSameOriginWindowChain(childWindow);

    for (const windowChainEl of windowChain) {
      const windowInChain = windowChainEl.window.deref();
      top += windowInChain?.scrollY ?? 0;
      left += windowInChain?.scrollX ?? 0;

      if (windowInChain === ancestorWindow) {
        break;
      }

      if (!windowChainEl.iframeElement) {
        break;
      }

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

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

/**
 * Returns a sha-256 composed of `parentOrigin` and `salt` converted to base 32
 */