// 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 "re2/prefilter.h"
#include "re2/sparse_array.h"
#include "util/util.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;
    // TODO(junyer): Use std::unordered_set<Prefilter*> instead?
    // It should be trivial to get rid of the stringification...
    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.
        std::vector<int> 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 re2

#endif // RE2_PREFILTER_TREE_H_
