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      1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef UI_BASE_MODELS_TREE_NODE_ITERATOR_H_
      6 #define UI_BASE_MODELS_TREE_NODE_ITERATOR_H_
      7 
      8 #include <stack>
      9 
     10 #include "base/basictypes.h"
     11 #include "base/logging.h"
     12 
     13 namespace ui {
     14 
     15 // Iterator that iterates over the descendants of a node. The iteration does
     16 // not include the node itself, only the descendants. The following illustrates
     17 // typical usage:
     18 // while (iterator.has_next()) {
     19 //   Node* node = iterator.Next();
     20 //   // do something with node.
     21 // }
     22 template <class NodeType>
     23 class TreeNodeIterator {
     24  public:
     25   // This contructor accepts an optional filter function |prune| which could be
     26   // used to prune complete branches of the tree. The filter function will be
     27   // evaluated on each tree node and if it evaluates to true the node and all
     28   // its descendants will be skipped by the iterator.
     29   TreeNodeIterator(NodeType* node, bool (*prune)(NodeType*))
     30       : prune_(prune) {
     31     int index = 0;
     32 
     33     // Move forward through the children list until the first non prunable node.
     34     // This is to satisfy the iterator invariant that the current index in the
     35     // Position at the top of the _positions list must point to a node the
     36     // iterator will be returning.
     37     for (; index < node->child_count(); ++index)
     38       if (!prune || !prune(node->GetChild(index)))
     39         break;
     40 
     41     if (index < node->child_count())
     42       positions_.push(Position<NodeType>(node, index));
     43   }
     44 
     45   explicit TreeNodeIterator(NodeType* node) : prune_(NULL) {
     46     if (!node->empty())
     47       positions_.push(Position<NodeType>(node, 0));
     48   }
     49 
     50   // Returns true if there are more descendants.
     51   bool has_next() const { return !positions_.empty(); }
     52 
     53   // Returns the next descendant.
     54   NodeType* Next() {
     55     if (!has_next()) {
     56       NOTREACHED();
     57       return NULL;
     58     }
     59 
     60     // There must always be a valid node in the current Position index.
     61     NodeType* result = positions_.top().node->GetChild(positions_.top().index);
     62 
     63     // Make sure we don't attempt to visit result again.
     64     positions_.top().index++;
     65 
     66     // Iterate over result's children.
     67     positions_.push(Position<NodeType>(result, 0));
     68 
     69     // Advance to next valid node by skipping over the pruned nodes and the
     70     // empty Positions. At the end of this loop two cases are possible:
     71     // - the current index of the top() Position points to a valid node
     72     // - the _position list is empty, the iterator has_next() will return false.
     73     while (!positions_.empty()) {
     74       if (positions_.top().index >= positions_.top().node->child_count())
     75         positions_.pop(); // This Position is all processed, move to the next.
     76       else if (prune_ &&
     77           prune_(positions_.top().node->GetChild(positions_.top().index)))
     78         positions_.top().index++;  // Prune the branch.
     79       else
     80         break;  // Now positioned at the next node to be returned.
     81     }
     82 
     83     return result;
     84   }
     85 
     86  private:
     87   template <class PositionNodeType>
     88   struct Position {
     89     Position(PositionNodeType* node, int index) : node(node), index(index) {}
     90     Position() : node(NULL), index(-1) {}
     91 
     92     PositionNodeType* node;
     93     int index;
     94   };
     95 
     96   std::stack<Position<NodeType> > positions_;
     97   bool (*prune_)(NodeType*);
     98 
     99   DISALLOW_COPY_AND_ASSIGN(TreeNodeIterator);
    100 };
    101 
    102 }  // namespace ui
    103 
    104 #endif  // UI_BASE_MODELS_TREE_NODE_ITERATOR_H_
    105