gecko/layout/base/nsChildIterator.h

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/*
 * used by nsCSSFrameConstructor to determine and iterate the child list
 * used to construct frames (normal children or something from XBL)
 */

#include "nsCOMPtr.h"
#include "nsIContent.h"
#include "nsINodeList.h"

/**
 * Helper class for iterating children during frame construction.
 * This class should always be used in lieu of the straight content
 * node APIs, since it handles XBL-generated anonymous content as
 * well.
 */
class NS_STACK_CLASS ChildIterator
{
protected:
  // We could just use a mNodes for the case when we're not dealing with XBL
  // anon content too, but in practice that would basically replace our current
  // branch on mNodes with an extra virtual function call in the common case.

  nsIContent* mContent;
  PRUint32 mIndex;
  nsINodeList* mNodes;

public:
  ChildIterator()
    : mContent(nsnull), mIndex(0), mNodes(nsnull) {}

  ChildIterator(const ChildIterator& aOther)
    : mContent(aOther.mContent),
      mIndex(aOther.mIndex),
      mNodes(aOther.mNodes) {}

  ChildIterator& operator=(const ChildIterator& aOther) {
    mContent = aOther.mContent;
    mIndex = aOther.mIndex;
    mNodes = aOther.mNodes;
    return *this;
  }

  ChildIterator& operator++() {
    ++mIndex;
    return *this;
  }

  ChildIterator operator++(int) {
    ChildIterator result(*this);
    ++mIndex;
    return result;
  }

  ChildIterator& operator--() {
    --mIndex;
    return *this;
  }

  ChildIterator operator--(int) {
    ChildIterator result(*this);
    --mIndex;
    return result;
  }

  nsIContent* get() const {
    if (XBLInvolved()) {
      return mNodes->GetNodeAt(mIndex);
    }

    return mContent->GetChildAt(mIndex);
  }

  nsIContent* operator*() const { return get(); }

  PRBool operator==(const ChildIterator& aOther) const {
    return mContent == aOther.mContent && mIndex == aOther.mIndex;
  }

  PRBool operator!=(const ChildIterator& aOther) const {
    return !aOther.operator==(*this);
  }

  PRUint32 position() {
    return mIndex;
  }

  void seek(PRUint32 aIndex) {
    // Make sure that aIndex is reasonable.  This should be |#ifdef
    // DEBUG|, but we need these numbers for the temporary workaround
    // for bug 133219.
    PRUint32 l = length();

    NS_ASSERTION(PRInt32(aIndex) >= 0 && aIndex <= l, "out of bounds");

    // Temporary workaround for bug 133219.
    if (aIndex > l)
      aIndex = l;

    mIndex = aIndex;
  }

  void seek(nsIContent* aContent) {
    PRInt32 index;
    if (XBLInvolved()) {
      index = mNodes->IndexOf(aContent);
    } else {
      index = mContent->IndexOf(aContent);
    }
    // XXXbz I wish we could assert that index != -1, but I think that's not
    // necessarily the case when called from ContentInserted if first-letter
    // frames are about.  It also seems to not be the case in some XBL cases
    // with filtered insertion points and no default insertion point.  I will
    // now claim that XBL's management of its insertion points is broken in
    // those cases, since it's returning an insertion parent for a node that
    // doesn't actually have the node in its child list according to
    // ChildIterator.  See bug 474324.
    if (index != -1) {
      mIndex = index;
    } else {
      // If aContent isn't going to get hit by this iterator, just seek to the
      // end of the list for lack of anything better to do.
      mIndex = length();
    }
  }

  PRBool XBLInvolved() const { return mNodes != nsnull; }

  /**
   * Create a pair of ChildIterators for a content node. aFirst will
   * point to the first child of aContent; aLast will point one past
   * the last child of aContent.
   */
  static nsresult Init(nsIContent*    aContent,
                       ChildIterator* aFirst,
                       ChildIterator* aLast);

private:
  PRUint32 length() {
    PRUint32 l;
    if (XBLInvolved()) {
      mNodes->GetLength(&l);
    } else {
      l = mContent->GetChildCount();
    }
    return l;
  }
};