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+// Copyright 2009 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef RE2_PREFILTER_TREE_H_
+#define RE2_PREFILTER_TREE_H_
+
+// The PrefilterTree class is used to form an AND-OR tree of strings
+// that would trigger each regexp. The 'prefilter' of each regexp is
+// added to PrefilterTree, and then PrefilterTree is used to find all
+// the unique strings across the prefilters. During search, by using
+// matches from a string matching engine, PrefilterTree deduces the
+// set of regexps that are to be triggered. The 'string matching
+// engine' itself is outside of this class, and the caller can use any
+// favorite engine. PrefilterTree provides a set of strings (called
+// atoms) that the user of this class should use to do the string
+// matching.
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include "util/util.h"
+#include "re2/prefilter.h"
+#include "re2/sparse_array.h"
+
+namespace re2 {
+
+class PrefilterTree {
+ public:
+  PrefilterTree();
+  explicit PrefilterTree(int min_atom_len);
+  ~PrefilterTree();
+
+  // Adds the prefilter for the next regexp. Note that we assume that
+  // Add called sequentially for all regexps. All Add calls
+  // must precede Compile.
+  void Add(Prefilter* prefilter);
+
+  // The Compile returns a vector of string in atom_vec.
+  // Call this after all the prefilters are added through Add.
+  // No calls to Add after Compile are allowed.
+  // The caller should use the returned set of strings to do string matching.
+  // Each time a string matches, the corresponding index then has to be
+  // and passed to RegexpsGivenStrings below.
+  void Compile(std::vector<std::string>* atom_vec);
+
+  // Given the indices of the atoms that matched, returns the indexes
+  // of regexps that should be searched.  The matched_atoms should
+  // contain all the ids of string atoms that were found to match the
+  // content. The caller can use any string match engine to perform
+  // this function. This function is thread safe.
+  void RegexpsGivenStrings(const std::vector<int>& matched_atoms,
+                           std::vector<int>* regexps) const;
+
+  // Print debug prefilter. Also prints unique ids associated with
+  // nodes of the prefilter of the regexp.
+  void PrintPrefilter(int regexpid);
+
+ private:
+  typedef SparseArray<int> IntMap;
+  typedef std::map<int, int> StdIntMap;
+  typedef std::map<std::string, Prefilter*> NodeMap;
+
+  // Each unique node has a corresponding Entry that helps in
+  // passing the matching trigger information along the tree.
+  struct Entry {
+   public:
+    // How many children should match before this node triggers the
+    // parent. For an atom and an OR node, this is 1 and for an AND
+    // node, it is the number of unique children.
+    int propagate_up_at_count;
+
+    // When this node is ready to trigger the parent, what are the indices
+    // of the parent nodes to trigger. The reason there may be more than
+    // one is because of sharing. For example (abc | def) and (xyz | def)
+    // are two different nodes, but they share the atom 'def'. So when
+    // 'def' matches, it triggers two parents, corresponding to the two
+    // different OR nodes.
+    StdIntMap* parents;
+
+    // When this node is ready to trigger the parent, what are the
+    // regexps that are triggered.
+    std::vector<int> regexps;
+  };
+
+  // Returns true if the prefilter node should be kept.
+  bool KeepNode(Prefilter* node) const;
+
+  // This function assigns unique ids to various parts of the
+  // prefilter, by looking at if these nodes are already in the
+  // PrefilterTree.
+  void AssignUniqueIds(NodeMap* nodes, std::vector<std::string>* atom_vec);
+
+  // Given the matching atoms, find the regexps to be triggered.
+  void PropagateMatch(const std::vector<int>& atom_ids,
+                      IntMap* regexps) const;
+
+  // Returns the prefilter node that has the same NodeString as this
+  // node. For the canonical node, returns node.
+  Prefilter* CanonicalNode(NodeMap* nodes, Prefilter* node);
+
+  // A string that uniquely identifies the node. Assumes that the
+  // children of node has already been assigned unique ids.
+  std::string NodeString(Prefilter* node) const;
+
+  // Recursively constructs a readable prefilter string.
+  std::string DebugNodeString(Prefilter* node) const;
+
+  // Used for debugging.
+  void PrintDebugInfo(NodeMap* nodes);
+
+  // These are all the nodes formed by Compile. Essentially, there is
+  // one node for each unique atom and each unique AND/OR node.
+  std::vector<Entry> entries_;
+
+  // indices of regexps that always pass through the filter (since we
+  // found no required literals in these regexps).
+  std::vector<int> unfiltered_;
+
+  // vector of Prefilter for all regexps.
+  std::vector<Prefilter*> prefilter_vec_;
+
+  // Atom index in returned strings to entry id mapping.
+  std::vector<int> atom_index_to_id_;
+
+  // Has the prefilter tree been compiled.
+  bool compiled_;
+
+  // Strings less than this length are not stored as atoms.
+  const int min_atom_len_;
+
+  PrefilterTree(const PrefilterTree&) = delete;
+  PrefilterTree& operator=(const PrefilterTree&) = delete;
+};
+
+}  // namespace
+
+#endif  // RE2_PREFILTER_TREE_H_