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#ifndef MOZC_CONVERTER_NBEST_GENERATOR_H_
#define MOZC_CONVERTER_NBEST_GENERATOR_H_

#include <cstdint>
#include <memory>
#include <string>
#include <vector>

#include "base/freelist.h"
#include "base/port.h"
#include "converter/candidate_filter.h"
#include "converter/segments.h"
#include "dictionary/pos_matcher.h"
#include "dictionary/suppression_dictionary.h"

namespace mozc {

class Connector;
class Lattice;
class Segmenter;
class SuggestionFilter;
struct Node;

class NBestGenerator {
 public:
  enum BoundaryCheckMode {
    // Boundary check mode.
    // For the case like;
    //   Candidate edge:      |  candidate  |
    //   Nodes:        |Node A|Node B|Node C|Node D|

    // For normal conversion.
    //  Candidate boundary is strictly same as inner boundary.
    // A-B: Should be the boundary
    // B-C: Should not be the boundary
    // C-D: Should be the boundary
    STRICT = 0,

    // For resegmented segment.
    //  Check mid point only.
    // A-B: Don't care
    // B-C: Should not be the boundary
    // C-D: Don't care
    ONLY_MID,

    // For Realtime conversion ("私の名前は中野です").
    //  Check only for candidate edge.
    // A-B: Should be the boundary
    // B-C: Don't care
    // C-D: Should be the boundary
    ONLY_EDGE,
  };

  // Try to enumerate N-best results between begin_node and end_node.
  NBestGenerator(
      const dictionary::SuppressionDictionary *suppression_dictionary,
      const Segmenter *segmenter, const Connector *connector,
      const dictionary::POSMatcher *pos_matcher, const Lattice *lattice,
      const SuggestionFilter *suggestion_filter,
      bool apply_suggestion_filter_for_exact_match);
  ~NBestGenerator();

  // Reset the iterator status.
  void Reset(const Node *begin_node, const Node *end_node,
             const BoundaryCheckMode mode);

  // Iterator:
  // Can obtain N-best results by calling Next() in sequence.
  bool Next(const std::string &original_key, Segment::Candidate *candidate,
            Segments::RequestType request_type);

 private:
  enum BoundaryCheckResult {
    VALID = 0,
    VALID_WEAK_CONNECTED,  // Valid but should get penalty.
    INVALID,
  };

  typedef BoundaryCheckResult (NBestGenerator::*BoundaryChecker)(const Node *,
                                                                 const Node *,
                                                                 bool) const;

  struct QueueElement;
  struct QueueElementComparator;

  // This is just a priority_queue of const QueueElement*, but supports
  // more operations in addition to std::priority_queue.
  class Agenda {
   public:
    Agenda() {}
    ~Agenda() {}

    const QueueElement *Top() const { return priority_queue_.front(); }
    bool IsEmpty() const { return priority_queue_.empty(); }
    void Clear() { priority_queue_.clear(); }
    void Reserve(int size) { priority_queue_.reserve(size); }

    void Push(const QueueElement *element);
    void Pop();

   private:
    std::vector<const QueueElement *> priority_queue_;

    DISALLOW_COPY_AND_ASSIGN(Agenda);
  };

  int InsertTopResult(const std::string &original_key,
                      Segment::Candidate *candidate,
                      Segments::RequestType request_type);

  void MakeCandidate(Segment::Candidate *candidate, int32_t cost,
                     int32_t structure_cost, int32_t wcost,
                     const std::vector<const Node *> &nodes) const;

  // Helper functions for Next(). Checks node boundary conditions.
  BoundaryCheckResult CheckStrict(const Node *lnode, const Node *rnode,
                                  bool is_edge) const;
  BoundaryCheckResult CheckOnlyMid(const Node *lnode, const Node *rnode,
                                   bool is_edge) const;
  BoundaryCheckResult CheckOnlyEdge(const Node *lnode, const Node *rnode,
                                    bool is_edge) const;

  int GetTransitionCost(const Node *lnode, const Node *rnode) const;

  // Create queue element from freelist
  const QueueElement *CreateNewElement(const Node *node,
                                       const QueueElement *next, int32_t fx,
                                       int32_t gx, int32_t structure_gx,
                                       int32_t w_gx);

  // References to relevant modules.
  const dictionary::SuppressionDictionary *suppression_dictionary_;
  const Segmenter *segmenter_;
  const Connector *connector_;
  const dictionary::POSMatcher *pos_matcher_;
  const Lattice *lattice_;

  const Node *begin_node_;
  const Node *end_node_;

  Agenda agenda_;
  FreeList<QueueElement> freelist_;
  std::vector<const Node *> nodes_;
  std::unique_ptr<converter::CandidateFilter> filter_;
  bool viterbi_result_checked_;
  BoundaryCheckMode check_mode_;

  BoundaryChecker boundary_checker_;

  DISALLOW_COPY_AND_ASSIGN(NBestGenerator);
};

}  // namespace mozc

#endif  // MOZC_CONVERTER_NBEST_GENERATOR_H_
