/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

#pragma once

#include <atomic>

#include "Recognizer.h"
#include "atn/ATN.h"
#include "atn/ATNState.h"

namespace antlr4 {
namespace atn {

  struct PredictionContextHasher;
  struct PredictionContextComparer;
  class PredictionContextMergeCache;

  typedef std::unordered_set<Ref<PredictionContext>, PredictionContextHasher, PredictionContextComparer> PredictionContextCache;

  class ANTLR4CPP_PUBLIC PredictionContext {
  public:
    /// Represents $ in local context prediction, which means wildcard.
    /// *+x = *.
    static const Ref<PredictionContext> EMPTY;

    /// Represents $ in an array in full context mode, when $
    /// doesn't mean wildcard: $ + x = [$,x]. Here,
    /// $ = EMPTY_RETURN_STATE.
    // ml: originally Integer.MAX_VALUE, which would be -1 for us, but this is already used in places where
    //     -1 is converted to unsigned, so we use a different value here. Any value does the job provided it doesn't
    //     conflict with real return states.
#if __cplusplus >= 201703L
    static constexpr size_t EMPTY_RETURN_STATE = std::numeric_limits<size_t>::max() - 9;
#else
    enum : size_t {
      EMPTY_RETURN_STATE = static_cast<size_t>(-10), // std::numeric_limits<size_t>::max() - 9; doesn't work in VS 2013
    };
#endif

  private:
#if __cplusplus >= 201703L
    static constexpr size_t INITIAL_HASH = 1;
#else
    enum : size_t {
      INITIAL_HASH = 1,
    };
#endif

  public:
    static std::atomic<size_t> globalNodeCount;
    const size_t id;

    /// <summary>
    /// Stores the computed hash code of this <seealso cref="PredictionContext"/>. The hash
    /// code is computed in parts to match the following reference algorithm.
    ///
    /// <pre>
    ///  private int referenceHashCode() {
    ///      int hash = <seealso cref="MurmurHash#initialize"/>(<seealso cref="#INITIAL_HASH"/>);
    ///
    ///      for (int i = 0; i < <seealso cref="#size()"/>; i++) {
    ///          hash = <seealso cref="MurmurHash#update"/>(hash, <seealso cref="#getParent"/>(i));
    ///      }
    ///
    ///      for (int i = 0; i < <seealso cref="#size()"/>; i++) {
    ///          hash = <seealso cref="MurmurHash#update"/>(hash, <seealso cref="#getReturnState"/>(i));
    ///      }
    ///
    ///      hash = <seealso cref="MurmurHash#finish"/>(hash, 2 * <seealso cref="#size()"/>);
    ///      return hash;
    ///  }
    /// </pre>
    /// </summary>
    const size_t cachedHashCode;

  protected:
    PredictionContext(size_t cachedHashCode);
    ~PredictionContext();

  public:
    /// Convert a RuleContext tree to a PredictionContext graph.
    /// Return EMPTY if outerContext is empty.
    static Ref<PredictionContext> fromRuleContext(const ATN &atn, RuleContext *outerContext);

    virtual size_t size() const = 0;
    virtual Ref<PredictionContext> getParent(size_t index) const = 0;
    virtual size_t getReturnState(size_t index) const = 0;

    virtual bool operator == (const PredictionContext &o) const = 0;

    /// This means only the EMPTY (wildcard? not sure) context is in set.
    virtual bool isEmpty() const;
    virtual bool hasEmptyPath() const;
    virtual size_t hashCode() const;

  protected:
    static size_t calculateEmptyHashCode();
    static size_t calculateHashCode(Ref<PredictionContext> parent, size_t returnState);
    static size_t calculateHashCode(const std::vector<Ref<PredictionContext>> &parents,
                                    const std::vector<size_t> &returnStates);

  public:
    // dispatch
    static Ref<PredictionContext> merge(const Ref<PredictionContext> &a, const Ref<PredictionContext> &b,
                                        bool rootIsWildcard, PredictionContextMergeCache *mergeCache);

    /// <summary>
    /// Merge two <seealso cref="SingletonPredictionContext"/> instances.
    ///
    /// <p/>
    ///
    /// Stack tops equal, parents merge is same; return left graph.<br/>
    /// <embed src="images/SingletonMerge_SameRootSamePar.svg" type="image/svg+xml"/>
    ///
    /// <p/>
    ///
    /// Same stack top, parents differ; merge parents giving array node, then
    /// remainders of those graphs. A new root node is created to point to the
    /// merged parents.<br/>
    /// <embed src="images/SingletonMerge_SameRootDiffPar.svg" type="image/svg+xml"/>
    ///
    /// <p/>
    ///
    /// Different stack tops pointing to same parent. Make array node for the
    /// root where both element in the root point to the same (original)
    /// parent.<br/>
    /// <embed src="images/SingletonMerge_DiffRootSamePar.svg" type="image/svg+xml"/>
    ///
    /// <p/>
    ///
    /// Different stack tops pointing to different parents. Make array node for
    /// the root where each element points to the corresponding original
    /// parent.<br/>
    /// <embed src="images/SingletonMerge_DiffRootDiffPar.svg" type="image/svg+xml"/>
    /// </summary>
    /// <param name="a"> the first <seealso cref="SingletonPredictionContext"/> </param>
    /// <param name="b"> the second <seealso cref="SingletonPredictionContext"/> </param>
    /// <param name="rootIsWildcard"> {@code true} if this is a local-context merge,
    /// otherwise false to indicate a full-context merge </param>
    /// <param name="mergeCache"> </param>
    static Ref<PredictionContext> mergeSingletons(const Ref<SingletonPredictionContext> &a,
      const Ref<SingletonPredictionContext> &b, bool rootIsWildcard, PredictionContextMergeCache *mergeCache);

    /**
     * Handle case where at least one of {@code a} or {@code b} is
     * {@link #EMPTY}. In the following diagrams, the symbol {@code $} is used
     * to represent {@link #EMPTY}.
     *
     * <h2>Local-Context Merges</h2>
     *
     * <p>These local-context merge operations are used when {@code rootIsWildcard}
     * is true.</p>
     *
     * <p>{@link #EMPTY} is superset of any graph; return {@link #EMPTY}.<br>
     * <embed src="images/LocalMerge_EmptyRoot.svg" type="image/svg+xml"/></p>
     *
     * <p>{@link #EMPTY} and anything is {@code #EMPTY}, so merged parent is
     * {@code #EMPTY}; return left graph.<br>
     * <embed src="images/LocalMerge_EmptyParent.svg" type="image/svg+xml"/></p>
     *
     * <p>Special case of last merge if local context.<br>
     * <embed src="images/LocalMerge_DiffRoots.svg" type="image/svg+xml"/></p>
     *
     * <h2>Full-Context Merges</h2>
     *
     * <p>These full-context merge operations are used when {@code rootIsWildcard}
     * is false.</p>
     *
     * <p><embed src="images/FullMerge_EmptyRoots.svg" type="image/svg+xml"/></p>
     *
     * <p>Must keep all contexts; {@link #EMPTY} in array is a special value (and
     * null parent).<br>
     * <embed src="images/FullMerge_EmptyRoot.svg" type="image/svg+xml"/></p>
     *
     * <p><embed src="images/FullMerge_SameRoot.svg" type="image/svg+xml"/></p>
     *
     * @param a the first {@link SingletonPredictionContext}
     * @param b the second {@link SingletonPredictionContext}
     * @param rootIsWildcard {@code true} if this is a local-context merge,
     * otherwise false to indicate a full-context merge
     */
    static Ref<PredictionContext> mergeRoot(const Ref<SingletonPredictionContext> &a,
      const Ref<SingletonPredictionContext> &b, bool rootIsWildcard);

    /**
     * Merge two {@link ArrayPredictionContext} instances.
     *
     * <p>Different tops, different parents.<br>
     * <embed src="images/ArrayMerge_DiffTopDiffPar.svg" type="image/svg+xml"/></p>
     *
     * <p>Shared top, same parents.<br>
     * <embed src="images/ArrayMerge_ShareTopSamePar.svg" type="image/svg+xml"/></p>
     *
     * <p>Shared top, different parents.<br>
     * <embed src="images/ArrayMerge_ShareTopDiffPar.svg" type="image/svg+xml"/></p>
     *
     * <p>Shared top, all shared parents.<br>
     * <embed src="images/ArrayMerge_ShareTopSharePar.svg" type="image/svg+xml"/></p>
     *
     * <p>Equal tops, merge parents and reduce top to
     * {@link SingletonPredictionContext}.<br>
     * <embed src="images/ArrayMerge_EqualTop.svg" type="image/svg+xml"/></p>
     */
    static Ref<PredictionContext> mergeArrays(const Ref<ArrayPredictionContext> &a,
      const Ref<ArrayPredictionContext> &b, bool rootIsWildcard, PredictionContextMergeCache *mergeCache);

  protected:
    /// Make pass over all M parents; merge any equal() ones.
    /// @returns true if the list has been changed (i.e. duplicates where found).
    static bool combineCommonParents(std::vector<Ref<PredictionContext>> &parents);

  public:
    static std::string toDOTString(const Ref<PredictionContext> &context);

    static Ref<PredictionContext> getCachedContext(const Ref<PredictionContext> &context,
      PredictionContextCache &contextCache,
      std::map<Ref<PredictionContext>, Ref<PredictionContext>> &visited);

    // ter's recursive version of Sam's getAllNodes()
    static std::vector<Ref<PredictionContext>> getAllContextNodes(const Ref<PredictionContext> &context);
    static void getAllContextNodes_(const Ref<PredictionContext> &context,
      std::vector<Ref<PredictionContext>> &nodes, std::set<PredictionContext *> &visited);

    virtual std::string toString() const;
    virtual std::string toString(Recognizer *recog) const;

    std::vector<std::string> toStrings(Recognizer *recognizer, int currentState);
    std::vector<std::string> toStrings(Recognizer *recognizer, const Ref<PredictionContext> &stop, int currentState);
  };

  struct PredictionContextHasher {
    size_t operator () (const Ref<PredictionContext> &k) const {
      return k->hashCode();
    }
  };

  struct PredictionContextComparer {
    bool operator () (const Ref<PredictionContext> &lhs, const Ref<PredictionContext> &rhs) const
    {
      if (lhs == rhs) // Object identity.
        return true;
      return (lhs->hashCode() == rhs->hashCode()) && (*lhs == *rhs);
    }
  };

  class PredictionContextMergeCache {
  public:
    Ref<PredictionContext> put(Ref<PredictionContext> const& key1, Ref<PredictionContext> const& key2,
                               Ref<PredictionContext> const& value);
    Ref<PredictionContext> get(Ref<PredictionContext> const& key1, Ref<PredictionContext> const& key2);

    void clear();
    std::string toString() const;
    size_t count() const;

  private:
    std::unordered_map<Ref<PredictionContext>,
      std::unordered_map<Ref<PredictionContext>, Ref<PredictionContext>, PredictionContextHasher, PredictionContextComparer>,
      PredictionContextHasher, PredictionContextComparer> _data;

  };

} // namespace atn
} // namespace antlr4

