michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=2 sw=2 et tw=78: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef NSREFERENCEDELEMENT_H_
michael@0: #define NSREFERENCEDELEMENT_H_
michael@0: 
michael@0: #include "mozilla/Attributes.h"
michael@0: #include "mozilla/dom/Element.h"
michael@0: #include "nsIAtom.h"
michael@0: #include "nsIDocument.h"
michael@0: #include "nsThreadUtils.h"
michael@0: #include "nsAutoPtr.h"
michael@0: 
michael@0: class nsIURI;
michael@0: class nsCycleCollectionCallback;
michael@0: 
michael@0: /**
michael@0:  * Class to track what element is referenced by a given ID.
michael@0:  * 
michael@0:  * To use it, call Reset() to set it up to watch a given URI. Call get()
michael@0:  * anytime to determine the referenced element (which may be null if
michael@0:  * the element isn't found). When the element changes, ElementChanged
michael@0:  * will be called, so subclass this class if you want to receive that
michael@0:  * notification. ElementChanged runs at safe-for-script time, i.e. outside
michael@0:  * of the content update. Call Unlink() if you want to stop watching
michael@0:  * for changes (get() will then return null).
michael@0:  *
michael@0:  * By default this is a single-shot tracker --- i.e., when ElementChanged
michael@0:  * fires, we will automatically stop tracking. get() will continue to return
michael@0:  * the changed-to element.
michael@0:  * Override IsPersistent to return true if you want to keep tracking after
michael@0:  * the first change.
michael@0:  */
michael@0: class nsReferencedElement {
michael@0: public:
michael@0:   typedef mozilla::dom::Element Element;
michael@0: 
michael@0:   nsReferencedElement() {}
michael@0:   ~nsReferencedElement() {
michael@0:     Unlink();
michael@0:   }
michael@0: 
michael@0:   /**
michael@0:    * Find which element, if any, is referenced.
michael@0:    */
michael@0:   Element* get() { return mElement; }
michael@0: 
michael@0:   /**
michael@0:    * Set up the reference. This can be called multiple times to
michael@0:    * change which reference is being tracked, but these changes
michael@0:    * do not trigger ElementChanged.
michael@0:    * @param aFrom the source element for context
michael@0:    * @param aURI the URI containing a hash-reference to the element
michael@0:    * @param aWatch if false, then we do not set up the notifications to track
michael@0:    * changes, so ElementChanged won't fire and get() will always return the same
michael@0:    * value, the current element for the ID.
michael@0:    * @param aReferenceImage whether the ID references image elements which are
michael@0:    * subject to the document's mozSetImageElement overriding mechanism.
michael@0:    */
michael@0:   void Reset(nsIContent* aFrom, nsIURI* aURI, bool aWatch = true,
michael@0:              bool aReferenceImage = false);
michael@0: 
michael@0:   /**
michael@0:    * A variation on Reset() to set up a reference that consists of the ID of
michael@0:    * an element in the same document as aFrom.
michael@0:    * @param aFrom the source element for context
michael@0:    * @param aID the ID of the element
michael@0:    * @param aWatch if false, then we do not set up the notifications to track
michael@0:    * changes, so ElementChanged won't fire and get() will always return the same
michael@0:    * value, the current element for the ID.
michael@0:    */
michael@0:   void ResetWithID(nsIContent* aFrom, const nsString& aID,
michael@0:                    bool aWatch = true);
michael@0: 
michael@0:   /**
michael@0:    * Clears the reference. ElementChanged is not triggered. get() will return
michael@0:    * null.
michael@0:    */
michael@0:   void Unlink();
michael@0: 
michael@0:   void Traverse(nsCycleCollectionTraversalCallback* aCB);
michael@0:   
michael@0: protected:
michael@0:   /**
michael@0:    * Override this to be notified of element changes. Don't forget
michael@0:    * to call this superclass method to change mElement. This is called
michael@0:    * at script-runnable time.
michael@0:    */
michael@0:   virtual void ElementChanged(Element* aFrom, Element* aTo) {
michael@0:     mElement = aTo;
michael@0:   }
michael@0: 
michael@0:   /**
michael@0:    * Override this to convert from a single-shot notification to
michael@0:    * a persistent notification.
michael@0:    */
michael@0:   virtual bool IsPersistent() { return false; }
michael@0: 
michael@0:   /**
michael@0:    * Set ourselves up with our new document.  Note that aDocument might be
michael@0:    * null.  Either aWatch must be false or aRef must be empty.
michael@0:    */
michael@0:   void HaveNewDocument(nsIDocument* aDocument, bool aWatch,
michael@0:                        const nsString& aRef);
michael@0:   
michael@0: private:
michael@0:   static bool Observe(Element* aOldElement,
michael@0:                         Element* aNewElement, void* aData);
michael@0: 
michael@0:   class Notification : public nsISupports {
michael@0:   public:
michael@0:     virtual void SetTo(Element* aTo) = 0;
michael@0:     virtual void Clear() { mTarget = nullptr; }
michael@0:     virtual ~Notification() {}
michael@0:   protected:
michael@0:     Notification(nsReferencedElement* aTarget)
michael@0:       : mTarget(aTarget)
michael@0:     {
michael@0:       NS_PRECONDITION(aTarget, "Must have a target");
michael@0:     }
michael@0:     nsReferencedElement* mTarget;
michael@0:   };
michael@0: 
michael@0:   class ChangeNotification : public nsRunnable,
michael@0:                              public Notification
michael@0:   {
michael@0:   public:
michael@0:     ChangeNotification(nsReferencedElement* aTarget,
michael@0:                        Element* aFrom, Element* aTo)
michael@0:       : Notification(aTarget), mFrom(aFrom), mTo(aTo)
michael@0:     {}
michael@0:     virtual ~ChangeNotification() {}
michael@0: 
michael@0:     NS_DECL_ISUPPORTS_INHERITED
michael@0:     NS_IMETHOD Run() MOZ_OVERRIDE {
michael@0:       if (mTarget) {
michael@0:         mTarget->mPendingNotification = nullptr;
michael@0:         mTarget->ElementChanged(mFrom, mTo);
michael@0:       }
michael@0:       return NS_OK;
michael@0:     }
michael@0:     virtual void SetTo(Element* aTo) { mTo = aTo; }
michael@0:     virtual void Clear()
michael@0:     {
michael@0:       Notification::Clear(); mFrom = nullptr; mTo = nullptr;
michael@0:     }
michael@0:   protected:
michael@0:     nsRefPtr<Element> mFrom;
michael@0:     nsRefPtr<Element> mTo;
michael@0:   };
michael@0:   friend class ChangeNotification;
michael@0: 
michael@0:   class DocumentLoadNotification : public Notification,
michael@0:                                    public nsIObserver
michael@0:   {
michael@0:   public:
michael@0:     DocumentLoadNotification(nsReferencedElement* aTarget,
michael@0:                              const nsString& aRef) :
michael@0:       Notification(aTarget)
michael@0:     {
michael@0:       if (!mTarget->IsPersistent()) {
michael@0:         mRef = aRef;
michael@0:       }
michael@0:     }
michael@0:     virtual ~DocumentLoadNotification() {}
michael@0: 
michael@0:     NS_DECL_ISUPPORTS
michael@0:     NS_DECL_NSIOBSERVER
michael@0:   private:
michael@0:     virtual void SetTo(Element* aTo) { }
michael@0: 
michael@0:     nsString mRef;
michael@0:   };
michael@0:   friend class DocumentLoadNotification;
michael@0:   
michael@0:   nsCOMPtr<nsIAtom>      mWatchID;
michael@0:   nsCOMPtr<nsIDocument>  mWatchDocument;
michael@0:   nsRefPtr<Element> mElement;
michael@0:   nsRefPtr<Notification> mPendingNotification;
michael@0:   bool                   mReferencingImage;
michael@0: };
michael@0: 
michael@0: #endif /*NSREFERENCEDELEMENT_H_*/