/******************************************************************************

 * Top contributors (to current version):

 *   Andrew Reynolds, Mathias Preiner

 *

 * This file is part of the cvc5 project.

 *

 * Copyright (c) 2009-2021 by the authors listed in the file AUTHORS

 * in the top-level source directory and their institutional affiliations.

 * All rights reserved.  See the file COPYING in the top-level source

 * directory for licensing information.

 * ****************************************************************************

 *

 * sygus_enumerator

 */

#include "cvc5_private.h"

#ifndef CVC5__THEORY__QUANTIFIERS__SYGUS_ENUMERATOR_H

#define CVC5__THEORY__QUANTIFIERS__SYGUS_ENUMERATOR_H

#include <map>

#include <unordered_set>

#include "expr/node.h"

#include "expr/type_node.h"

#include "theory/quantifiers/sygus/synth_conjecture.h"

#include "theory/quantifiers/sygus/term_database_sygus.h"

namespace cvc5 {

namespace theory {

namespace quantifiers {

class SynthConjecture;

class SygusPbe;

/** SygusEnumerator

 *

 * This class is used for enumerating all terms of a sygus datatype type. At

 * a high level, it is used as an alternative approach to sygus datatypes

 * solver as a candidate generator in a synthesis loop. It filters terms based

 * on redundancy criteria, for instance, it does not generate two terms whose

 * builtin terms (TermDb::sygusToBuiltin) can be shown to be equivalent via

 * rewriting. It enumerates terms in order of sygus term size

 * (TermDb::getSygusTermSize).

 *

 * It also can be configured to enumerates sygus terms with free variables,

 * (as opposed to variables bound in the formal arguments list of the

 * function-to-synthesize), where each free variable appears in exactly one

 * subterm. For grammar:

 *   S -> 0 | 1 | x | S+S

 * this enumerator will generate the stream:

 *   z1, C_0, C_1, C_x, C_+(z1, z2), C_+(z1, C_1), C_+(C_1, C_1) ...

 * and so on, where z1 and z2 are variables of sygus datatype type S. We call

 * these "shapes". This feature can be enabled by setting enumShapes to true

 * in the constructor below.

 */

class SygusEnumerator : public EnumValGenerator

{

 public:

  SygusEnumerator(TermDbSygus* tds,

                  SynthConjecture* p,

                  SygusStatistics& s,

                  bool enumShapes = false);

  /** initialize this class with enumerator e */

  void initialize(Node e) override;

  /** Inform this generator that abstract value v was enumerated. */

  void addValue(Node v) override;

  /** increment */

  bool increment() override;

  /** Get the next concrete value generated by this class. */

  Node getCurrent() override;

  /** Are we enumerating shapes? */

  bool isEnumShapes() const;

 private:

  /** pointer to term database sygus */

  TermDbSygus* d_tds;

  /** pointer to the synth conjecture that owns this enumerator */

  SynthConjecture* d_parent;

  /** reference to the statistics of parent */

  SygusStatistics& d_stats;

  /** Whether we are enumerating shapes */

  bool d_enumShapes;

  /** Term cache

   *

   * This stores a list of terms for a given sygus type. The key features of

   * this data structure are that terms are stored in order of size,

   * indices can be recorded that indicate where terms of size n begin for each

   * natural number n, and redundancy criteria are used for discarding terms

   * that are not relevant. This includes discarding terms whose builtin version

   * is the same up to T-rewriting with another, or is equivalent under

   * examples, if the conjecture in question is in examples form and

   * sygusSymBreakPbe is enabled.

   *

   * This class also computes static information about sygus types that is

   * relevant for enumeration. Primarily, this includes mapping constructors

   * to "constructor classes". Two sygus constructors can be placed in the same

   * constructor class if their constructor weight is equal, and the tuple

   * of their argument types are the same. For example, for:

   *   A -> A+B | A-B | A*B | A+A | A | x

   * The first three constructors above can be placed in the same constructor

   * class, assuming they have identical weights. Constructor classes are used

   * as an optimization when enumerating terms, since they expect the same

   * tuple of argument terms for constructing a term of a fixed size.

   *

   * Constructor classes are allocated such that the constructor weights are

   * in ascending order. This allows us to avoid constructors whose weight

   * is greater than n while we are trying to enumerate terms of sizes strictly

   * less than n.

   *

   * Constructor class 0 is reserved for nullary operators with weight 0. This

   * is an optimization so that such constructors can be skipped for sizes

   * greater than 0, since we know all terms generated by these constructors

   * have size 0.

   */

  {

   public:

    TermCache();

    /** initialize this cache */

    void initialize(SygusStatistics* s,

                    Node e,

                    TypeNode tn,

                    TermDbSygus* tds,

                    ExampleEvalCache* ece = nullptr);

    /** get last constructor class index for weight

     *

     * This returns a minimal index n such that all constructor classes at

     * index < n have weight at most w.

     */

    unsigned getLastConstructorClassIndexForWeight(unsigned w) const;

    /** get num constructor classes */

    unsigned getNumConstructorClasses() const;

    /** get the constructor indices for constructor class i */

    void getConstructorClass(unsigned i, std::vector<unsigned>& cclass) const;

    /** get argument types for constructor class i */

    void getTypesForConstructorClass(unsigned i,

                                     std::vector<TypeNode>& types) const;

    /** get constructor weight for constructor class i */

    unsigned getWeightForConstructorClass(unsigned i) const;

    /**

     * Add sygus term n to this cache, return true if the term was unique based

     * on the redundancy criteria used by this class.

     */

    bool addTerm(Node n);

    /**

     * Indicate to this cache that we are finished enumerating terms of the

     * current size.

     */

    void pushEnumSizeIndex();

    /** Get the current size of terms that we are enumerating */

    unsigned getEnumSize() const;

    /** get the index at which size s terms start, where s <= getEnumSize() */

    unsigned getIndexForSize(unsigned s) const;

    /** get the index^th term successfully added to this cache */

    Node getTerm(unsigned index) const;

    /** get the number of terms successfully added to this cache */

    unsigned getNumTerms() const;

    /** are we finished enumerating terms? */

    bool isComplete() const;

    /** set that we are finished enumerating terms */

    void setComplete();

   private:

    /** reference to the statistics of parent */

    SygusStatistics* d_stats;

    /** the enumerator this cache is for */

    Node d_enum;

    /** the sygus type of terms in this cache */

    TypeNode d_tn;

    /** pointer to term database sygus */

    TermDbSygus* d_tds;

    /**

     * Pointer to the example evaluation cache utility (used for symmetry

     * breaking).

     */

    ExampleEvalCache* d_eec;

    //-------------------------static information about type

    /** is d_tn a sygus type? */

    bool d_isSygusType;

    /** number of constructor classes */

    unsigned d_numConClasses;

    /** Map from weights to the starting constructor class for that weight. */

    std::map<unsigned, unsigned> d_weightToCcIndex;

    /** Information for each constructor class */

    class ConstructorClass

    {

     public:

      /** The indices of the constructors in this constructor class */

      std::vector<unsigned> d_cons;

      /** The argument types of the constructor class */

      std::vector<TypeNode> d_types;

      /** Constructor weight */

      unsigned d_weight;

    };

    std::map<unsigned, ConstructorClass> d_cclass;

    /** constructor to indices */

    std::map<unsigned, std::vector<unsigned>> d_cToCIndices;

    //-------------------------end static information about type

    /** the list of sygus terms we have enumerated */

    std::vector<Node> d_terms;

    /** the set of builtin terms corresponding to the above list */

    std::unordered_set<Node> d_bterms;

    /**

     * The index of first term whose size is greater than or equal to that size,

     * if it exists.

     */

    std::map<unsigned, unsigned> d_sizeStartIndex;

    /** the maximum size of terms we have stored in this cache so far */

    unsigned d_sizeEnum;

    /** whether this term cache is complete */

    bool d_isComplete;

    /** sampler (for --sygus-rr-verify) */

    quantifiers::SygusSampler d_samplerRrV;

    /** is the above sampler initialized? */

    bool d_sampleRrVInit;

  };

  /** above cache for each sygus type */

  std::map<TypeNode, TermCache> d_tcache;

  /** initialize term cache for type tn */

  void initializeTermCache(TypeNode tn);

  /** virtual class for term enumerators */

  class TermEnum

  {

   public:

    TermEnum();

    /** get the current size of terms we are enumerating */

    unsigned getCurrentSize();

    /** get the current term of the enumerator */

    virtual Node getCurrent() = 0;

    /** increment the enumerator, return false if the enumerator is finished */

    virtual bool increment() = 0;

   protected:

    /** pointer to the sygus enumerator class */

    SygusEnumerator* d_se;

    /** the (sygus) type of terms we are enumerating */

    TypeNode d_tn;

    /** the current size of terms we are enumerating */

    unsigned d_currSize;

  };

  class TermEnumMaster;

  /** A "slave" enumerator

   *

   * A slave enumerator simply iterates over an index in a given term cache,

   * and relies on a pointer to a "master" enumerator to generate new terms

   * whenever necessary.

   *

   * This class maintains the following invariants, for tc=d_se->d_tcache[d_tn]:

   * (1) d_index < tc.getNumTerms(),

   * (2) d_currSize is the term size of tc.getTerm( d_index ),

   * (3) d_hasIndexNextEnd is (d_currSize < tc.getEnumSize()),

   * (4) If d_hasIndexNextEnd is true, then

   *       d_indexNextEnd = tc.getIndexForSize(d_currSize+1), and

   *       d_indexNextEnd > d_index.

   *

   * Intuitively, these invariants say (1) d_index is a valid index in the

   * term cache, (2) d_currSize is the sygus term size of getCurrent(), (3)

   * d_hasIndexNextEnd indicates whether d_indexNextEnd is valid, and (4)

   * d_indexNextEnd is the index in the term cache where terms of the current

   * size end, if such an index exists.

   */

  {

   public:

    TermEnumSlave();

    /**

     * Initialize this enumerator to enumerate terms of type tn whose size is in

     * the range [sizeMin, sizeMax], inclusive. If this function returns true,

     * then getCurrent() will return the first term in the stream, which is

     * non-empty. Further terms are generated by increment()/getCurrent().

     */

    bool initialize(SygusEnumerator* se,

                    TypeNode tn,

                    unsigned sizeMin,

                    unsigned sizeMax);

    /** get the current term of the enumerator */

    Node getCurrent() override;

    /** increment the enumerator */

    bool increment() override;

   private:

    /** the maximum size of terms this enumerator should enumerate */

    unsigned d_sizeLim;

    /** the current index in the term cache we are considering */

    unsigned d_index;

    /** the index in the term cache where terms of the current size end */

    unsigned d_indexNextEnd;

    /** whether d_indexNextEnd refers to a valid index */

    bool d_hasIndexNextEnd;

    /** pointer to the master enumerator of type d_tn */

    TermEnum* d_master;

    /** validate invariants on d_index, d_indexNextEnd, d_hasIndexNextEnd */

    bool validateIndex();

    /** validate invariants on  d_indexNextEnd, d_hasIndexNextEnd  */

    void validateIndexNextEnd();

  };

  /** Class for "master" enumerators

   *

   * This enumerator is used to generate new terms of a given type d_tn. It

   * generates all terms of type d_tn that are not redundant based on the

   * current criteria.

   *

   * To enumerate terms, this class performs the following steps as necessary

   * during a call to increment():

   * - Fix the size of terms "d_currSize" we are currently enumerating,

   * - Set the constructor class "d_consClassNum" whose constructors are the top

   * symbol of the current term we are constructing. All constructors from this

   * class have the same weight, which we store in d_ccWeight,

   * - Initialize the current children "d_children" so that the sum of their

   * current sizes is exactly (d_currSize - d_ccWeight),

   * - Increment the current set of children until a new tuple of terms is

   * considered,

   * - Set the constructor "d_consNum" from within the constructor class,

   * - Build the current term and check whether it is not redundant according

   * to the term cache of its type.

   *

   * We say this enumerator is active if initialize(...) returns true, and the

   * last call (if any) to increment returned true.

   *

   * This class maintains the following invariants, for tc=d_se->d_tcache[d_tn],

   * if it is active:

   * (1) getCurrent() is tc.getTerm(tc.getNumTerms()-1),

   * (2) tc.pushEnumSizeIndex() has been called by this class exactly

   * getCurrentSize() times.

   * In other words, (1) getCurrent() is always the last term in the term cache

   * of the type of this enumerator tc, and (2) the size counter of tc is in

   * sync with the current size of this enumerator, that is, the master

   * enumerator is responsible for communicating size boundaries to its term

   * cache.

   */

  {

   public:

    TermEnumMaster();

    /**

     * Initialize this enumerator to enumerate (all) terms of type tn, modulo

     * the redundancy criteria used by this class.

     */

    bool initialize(SygusEnumerator* se, TypeNode tn);

    /** get the current term of the enumerator */

    Node getCurrent() override;

    /** increment the enumerator

     *

     * Returns true if there are more terms to enumerate, in which case a

     * subsequent call to getCurrent() returns the next enumerated term. This

     * method returns false if the last call to increment() has yet to

     * terminate. This can happen for recursive datatypes where a slave

     * enumerator may request that this class increment the next term. We avoid

     * an infinite loop by guarding this with the d_isIncrementing flag and

     * return false.

     */

    bool increment() override;

   private:

    /** pointer to term database sygus */

    TermDbSygus* d_tds;

    /** are we enumerating shapes? */

    bool d_enumShapes;

    /** have we initialized the shape enumeration? */

    bool d_enumShapesInit;

    /** are we currently inside a increment() call? */

    bool d_isIncrementing;

    /** cache for getCurrent() */

    Node d_currTerm;

    /** is d_currTerm set */

    bool d_currTermSet;

    //----------------------------- current constructor class information

    /** the next constructor class we are using */

    unsigned d_consClassNum;

    /** the constructors in the current constructor class */

    std::vector<unsigned> d_ccCons;

    /** the types of the current constructor class */

    std::vector<TypeNode> d_ccTypes;

    /** the operator weight for the constructor class */

    unsigned d_ccWeight;

    //----------------------------- end current constructor class information

    /** If >0, 1 + the index in d_ccCons we are considering */

    unsigned d_consNum;

    /** the child enumerators for this enumerator */

    std::map<unsigned, TermEnumSlave> d_children;

    /** the current sum of current sizes of the enumerators in d_children */

    unsigned d_currChildSize;

    /**

     * The number of indices, starting from zero, in d_children that point to

     * initialized slave enumerators.

     */

    unsigned d_childrenValid;

    /** initialize children

     *

     * Initialize all the remaining uninitialized children of this enumerator.

     * If this method returns true, then each of d_children are

     * initialized to be slave enumerators of the argument types indicated by

     * d_ccTypes, and the sum of their current sizes (d_currChildSize) is

     * exactly (d_currSize - d_ccWeight). If this method returns false, then

     * it was not possible to initialize the children such that they meet the

     * size requirements, and such that the assignments from children to size

     * has not already been considered. In this case, all updates to d_children

     * are reverted and d_currChildSize and d_childrenValid are reset to their

     * values prior to this call.

     */

    bool initializeChildren();

    /** initialize child

     *

     * Initialize child i to enumerate terms whose size is at least sizeMin,

     * and whose maximum size is the largest size such that we can still

     * construct terms for the given constructor class and the current children

     * whose size is not more than the current size d_currSize. Additionally,

     * if i is the last child, we modify sizeMin such that it is exactly the

     * size of terms needed for the children to sum up to size d_currSize.

     */

    bool initializeChild(unsigned i, unsigned sizeMin);

    /** increment internal, helper for increment() */

    bool incrementInternal();

    /**

     * The vector children is a set of terms given to

     *    NodeManager::mkNode(APPLY_CONSTRUCTOR, children)

     * This converts children so that all sygus free variables are unique. Note

     * that the first child is a constructor operator and should be skipped.

     */

    void childrenToShape(std::vector<Node>& children);

    /**

     * Convert n into shape based on the variable counters. For example if

     * vcounter is { Int -> 7 }, then (+ x1 x2) is converted to (+ x7 x8) and

     * vouncter is updated to { Int -> 9 }.

     */

    Node convertShape(Node n, std::map<TypeNode, int>& vcounter);

  };

  /** an interpreted value enumerator

   *

   * This enumerator uses the builtin type enumerator for a given type. It

   * is used to fill in concrete holes into "any constant" constructors

   * when sygus-repair-const is not enabled. The number of terms of size n

   * is m^n, where m is configurable via --sygus-active-gen-enum-cfactor=m.

   */

  {

   public:

    TermEnumMasterInterp(TypeNode tn);

    /** initialize this enumerator */

    bool initialize(SygusEnumerator* se, TypeNode tn);

    /** get the current term of the enumerator */

    Node getCurrent() override;

    /** increment the enumerator */

    bool increment() override;

   private:

    /** the type enumerator */

    TypeEnumerator d_te;

    /** the current number of terms we are enumerating for the given size */

    unsigned d_currNumConsts;

    /** the next end threshold */

    unsigned d_nextIndexEnd;

  };

  /** a free variable enumerator

   *

   * This enumerator enumerates canonical free variables for a given type.

   * The n^th variable in this stream is assigned size n. This enumerator is

   * used in conjunction with sygus-repair-const to generate solutions with

   * constant holes. In this approach, free variables are arguments to

   * any-constant constructors. This is required so that terms with holes are

   * unique up to rewriting when appropriate.

   */

  {

   public:

    TermEnumMasterFv();

    /** initialize this enumerator */

    bool initialize(SygusEnumerator* se, TypeNode tn);

    /** get the current term of the enumerator */

    Node getCurrent() override;

    /** increment the enumerator */

    bool increment() override;

  };

  /** the master enumerator for each sygus type */

  std::map<TypeNode, TermEnumMaster> d_masterEnum;

  /** the master enumerator for each non-sygus type */

  std::map<TypeNode, TermEnumMasterFv> d_masterEnumFv;

  /** the master enumerator for each non-sygus type */

  std::map<TypeNode, std::unique_ptr<TermEnumMasterInterp>> d_masterEnumInt;

  /** the sygus enumerator this class is for */

  Node d_enum;

  /** the type of d_enum */

  TypeNode d_etype;

  /** pointer to the master enumerator of type d_etype */

  TermEnum* d_tlEnum;

  /** the abort size, caches the value of --sygus-abort-size */

  int d_abortSize;

  /** get master enumerator for type tn */

  TermEnum* getMasterEnumForType(TypeNode tn);

  //-------------------------------- externally specified symmetry breaking

  /** set of constructors we disallow at top level

   *

   * A constructor C is disallowed at the top level if a symmetry breaking

   * lemma that entails ~is-C( d_enum ) was registered to

   * TermDbSygus::registerSymBreakLemma.

   */

  std::unordered_set<Node> d_sbExcTlCons;

  //-------------------------------- end externally specified symmetry breaking

};

}  // namespace quantifiers

}  // namespace theory

}  // namespace cvc5

#endif /* CVC5__THEORY__QUANTIFIERS__SYGUS_ENUMERATOR_H */