/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "imgINotificationObserver.idl"

interface imgIRequest;
interface nsIChannel;
interface nsIStreamListener;
interface nsIURI;
interface nsIDocument;
interface nsIFrame;

/**
 * This interface represents a content node that loads images.  The interface
 * exists to allow getting information on the images that the content node
 * loads and to allow registration of observers for the image loads.
 *
 * Implementors of this interface should handle all the mechanics of actually
 * loading an image -- getting the URI, checking with content policies and
 * the security manager to see whether loading the URI is allowed, performing
 * the load, firing any DOM events as needed.
 *
 * An implementation of this interface may support the concepts of a
 * "current" image and a "pending" image.  If it does, a request to change
 * the currently loaded image will start a "pending" request which will
 * become current only when the image is loaded.  It is the responsibility of
 * observers to check which request they are getting notifications for.
 *
 * Observers added in mid-load will not get any notifications they
 * missed.  We should NOT freeze this interface without considering
 * this issue.  (It could be that the image status on imgIRequest is
 * sufficient, when combined with the imageBlockingStatus information.)
 *
 * Please make sure to update the MozImageLoadingContent WebIDL
 * interface to mirror this interface when changing it.
 */

[scriptable, builtinclass, uuid(e3968acd-b796-4ca3-aec0-e7f0880f2219)]
interface nsIImageLoadingContent : imgINotificationObserver
{
  /**
   * Request types.  Image loading content nodes attempt to do atomic
   * image changes when the image url is changed.  This means that
   * when the url changes the new image load will start, but the old
   * image will remain the "current" request until the new image is
   * fully loaded.  At that point, the old "current" request will be
   * discarded and the "pending" request will become "current".
   */
  const long UNKNOWN_REQUEST = -1;
  const long CURRENT_REQUEST = 0;
  const long PENDING_REQUEST = 1;

  /**
   * loadingEnabled is used to enable and disable loading in
   * situations where loading images is unwanted.  Note that enabling
   * loading will *not* automatically trigger an image load.
   */
  attribute boolean loadingEnabled;

  /**
   * Returns the image blocking status (@see nsIContentPolicy).  This
   * will always be an nsIContentPolicy REJECT_* status for cases when
   * the image was blocked.  This status always refers to the
   * CURRENT_REQUEST load.
   */
  readonly attribute short imageBlockingStatus;

  /**
   * Used to register an image decoder observer.  Typically, this will
   * be a proxy for a frame that wants to paint the image.
   * Notifications from ongoing image loads will be passed to all
   * registered observers.  Notifications for all request types,
   * current and pending, will be passed through.
   *
   * @param aObserver the observer to register
   *
   * @throws NS_ERROR_OUT_OF_MEMORY
   */
  void addObserver(in imgINotificationObserver aObserver);

  /**
   * Used to unregister an image decoder observer.
   *
   * @param aObserver the observer to unregister
   */
  void removeObserver(in imgINotificationObserver aObserver);
  
  /**
   * Accessor to get the image requests
   *
   * @param aRequestType a value saying which request is wanted
   *
   * @return the imgIRequest object (may be null, even when no error
   * is thrown)
   *
   * @throws NS_ERROR_UNEXPECTED if the request type requested is not
   * known
   */
  imgIRequest getRequest(in long aRequestType);

  /**
   * Used to notify the image loading content node that a frame has been
   * created.
   */
  [notxpcom] void frameCreated(in nsIFrame aFrame);

  /**
   * Used to notify the image loading content node that a frame has been
   * destroyed.
   */
  [notxpcom] void frameDestroyed(in nsIFrame aFrame);

  /**
   * Used to find out what type of request one is dealing with (eg
   * which request got passed through to the imgINotificationObserver
   * interface of an observer)
   *
   * @param aRequest the request whose type we want to know
   *
   * @return an enum value saying what type this request is
   *
   * @throws NS_ERROR_UNEXPECTED if aRequest is not known
   */
  long getRequestType(in imgIRequest aRequest);

  /**
   * Gets the URI of the current request, if available.
   * Otherwise, returns the last URI that this content tried to load, or
   * null if there haven't been any such attempts.
   */
  readonly attribute nsIURI currentURI;

  /**
   * loadImageWithChannel allows data from an existing channel to be
   * used as the image data for this content node.
   *
   * @param aChannel the channel that will deliver the data
   *
   * @return a stream listener to pump the image data into
   *
   * @see imgILoader::loadImageWithChannel
   *
   * @throws NS_ERROR_NULL_POINTER if aChannel is null
   */
  nsIStreamListener loadImageWithChannel(in nsIChannel aChannel);

  /**
   * forceReload forces reloading of the image pointed to by currentURI
   *
   * @throws NS_ERROR_NOT_AVAILABLE if there is no current URI to reload
   */
  void forceReload();

  /**
   * Enables/disables image state forcing. When |aForce| is PR_TRUE, we force
   * nsImageLoadingContent::ImageState() to return |aState|. Call again with |aForce|
   * as PR_FALSE to revert ImageState() to its original behaviour.
   */
  void forceImageState(in boolean aForce, in unsigned long long aState);

  /**
   * A visible count is stored, if it is non-zero then this image is considered
   * visible. These methods increment, decrement, or return the visible coount.
   */
  [noscript, notxpcom] void IncrementVisibleCount();
  [noscript, notxpcom] void DecrementVisibleCount();
  [noscript, notxpcom] uint32_t GetVisibleCount();
};
