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

 * Top contributors (to current version):

 *   Andrew Reynolds, Haniel Barbosa, Andres Noetzli

 *

 * 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.

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

 *

 * cegis with unification techinques.

 */

#include "cvc5_private.h"

#ifndef CVC5__THEORY__QUANTIFIERS__SYGUS__CEGIS_UNIF_H

#define CVC5__THEORY__QUANTIFIERS__SYGUS__CEGIS_UNIF_H

#include <map>

#include <vector>

#include "theory/decision_strategy.h"

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

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

namespace cvc5 {

namespace theory {

namespace quantifiers {

/** Cegis Unif Enumerators Decision Strategy

 *

 * This class enforces a decision strategy that limits the number of

 * unique values given to the set of heads of evaluation points and conditions

 * enumerators for these points, which are variables of sygus datatype type that

 * are introduced by CegisUnif.

 *

 * It maintains a set of guards, call them G_uq_1 ... G_uq_n, where the

 * semantics of G_uq_i is "for each type, the heads of evaluation points of that

 * type are interpreted as a value in a set whose cardinality is at most i".

 * We also enforce that the number of condition enumerators for evaluation

 * points is equal to (n-1).

 *

 * To enforce this, we introduce sygus enumerator(s) of the same type as the

 * heads of evaluation points and condition enumerators registered to this class

 * and add lemmas that enforce that these terms are equal to at least one

 * enumerator (see registerEvalPtAtSize).

 */

{

 public:

  CegisUnifEnumDecisionStrategy(QuantifiersState& qs,

                                QuantifiersInferenceManager& qim,

                                TermDbSygus* tds,

                                SynthConjecture* parent);

  /** Make the n^th literal of this strategy (G_uq_n).

   *

   * This call may add new lemmas of the form described above

   * registerEvalPtAtValue on the output channel of d_qe.

   */

  Node mkLiteral(unsigned n) override;

  /** identify */

  {

  }

  /** initialize candidates

   *

   * Notify this class that it will be managing enumerators for the vector

   * of strategy points es. This function should only be called once.

   *

   * Each strategy point in es should be such that we are using a

   * synthesis-by-unification approach for its candidate.

   */

  void initialize(const std::vector<Node>& es,

                  const std::map<Node, Node>& e_to_cond,

                  const std::map<Node, std::vector<Node>>& strategy_lemmas);

  /*

   * Do not hide the zero-argument version of initialize() inherited from the

   * base class

   */

  using DecisionStrategy::initialize;

  /** get the current set of enumerators for strategy point e

   *

   * Index 0 adds the set of return value enumerators to es, index 1 adds the

   * set of condition enumerators to es.

   */

  void getEnumeratorsForStrategyPt(Node e,

                                   std::vector<Node>& es,

                                   unsigned index) const;

  /** register evaluation point for candidate

   *

   * This notifies this class that eis is a set of heads of evaluation points

   * for strategy point e, where e was passed to initialize in the vector es.

   *

   * This may add new lemmas of the form described above

   * registerEvalPtAtSize on the output channel of d_qe.

   */

  void registerEvalPts(const std::vector<Node>& eis, Node e);

 private:

  /** Reference to the quantifiers inference manager */

  QuantifiersInferenceManager& d_qim;

  /** sygus term database of d_qe */

  TermDbSygus* d_tds;

  /** reference to the parent conjecture */

  SynthConjecture* d_parent;

  /**

   * Whether we are using condition pool enumeration (Section 4 of Barbosa et al

   * FMCAD 2019). This is determined by option::sygusUnifPi().

   */

  bool d_useCondPool;

  /** whether this module has been initialized */

  bool d_initialized;

  /** null node */

  Node d_null;

  /** information per initialized type */

  {

   public:

    /** strategy point for this type */

    Node d_pt;

    /** the set of enumerators we have allocated for this strategy point

     *

     * Index 0 stores the return value enumerators, and index 1 stores the

     * conditional enumerators. We have that

     *   d_enums[0].size()==d_enums[1].size()+1.

     */

    std::vector<Node> d_enums[2];

    /** the type of conditional enumerators for this strategy point  */

    TypeNode d_ce_type;

    /**

     * The set of evaluation points of this type. In models, we ensure that

     * each of these are equal to one of d_enums[0].

     */

    std::vector<Node> d_eval_points;

    /** symmetry breaking lemma template for this strategy point

     *

     * Each pair stores (the symmetry breaking lemma template, argument (to be

     * instantiated) of symmetry breaking lemma template).

     *

     * Index 0 stores the symmetry breaking lemma template for return values,

     * index 1 stores the template for conditions.

     */

    std::pair<Node, Node> d_sbt_lemma_tmpl[2];

  };

  /** map strategy points to the above info */

  std::map<Node, StrategyPtInfo> d_ce_info;

  /** the "virtual" enumerator

   *

   * This enumerator is used for enforcing fairness. In particular, we relate

   * its size to the number of conditions allocated by this class such that:

   *    ~G_uq_i => size(d_virtual_enum) >= floor( log2( i-1 ) )

   * In other words, if we are using (i-1) conditions in our solution,

   * the size of the virtual enumerator is at least the floor of the log (base

   * two) of (i-1). Due to the default fairness scheme in the quantifier-free

   * datatypes solver (if --sygus-fair-max is enabled), this ensures that other

   * enumerators are allowed to have at least this size. This affect other

   * fairness schemes in an analogous fashion. In particular, we enumerate

   * based on the tuples for (term size, #conditions):

   *   (0,0), (0,1)                                             [size 0]

   *   (0,2), (0,3), (1,1), (1,2), (1,3)                        [size 1]

   *   (0,4), ..., (0,7), (1,4), ..., (1,7), (2,0), ..., (2,7)  [size 2]

   *   (0,8), ..., (0,15), (1,8), ..., (1,15), ...              [size 3]

   */

  Node d_virtual_enum;

  /** Registers an enumerator and adds symmetry breaking lemmas

   *

   * The symmetry breaking lemmas are generated according to the stored

   * information from the enumerator's respective strategy point and whether it

   * is a condition or return value enumerator. For the latter we add symmetry

   * breaking lemmas that force enumerators to consider values in an increasing

   * order of size.

   */

  void setUpEnumerator(Node e, StrategyPtInfo& si, unsigned index);

  /** register evaluation point at size

   *

   * This sends a lemma of the form:

   *   G_uq_n => ei = d1 V ... V ei = dn

   * on the output channel of d_qe, where d1...dn are sygus enumerators of the

   * same type as e and ei, and ei is an evaluation point of strategy point e.

   */

  void registerEvalPtAtSize(Node e, Node ei, Node guq_lit, unsigned n);

};

/** Synthesizes functions in a data-driven SyGuS approach

 *

 * Data is derived from refinement lemmas generated through the regular CEGIS

 * approach. SyGuS is used to generate terms for classifying the data

 * (e.g. using decision tree learning) and thus generate a candidates for

 * functions-to-synthesize.

 *

 * This approach is inspired by the divide and conquer synthesis through

 * unification approach by Alur et al. TACAS 2017, by ICE-based invariant

 * synthesis from Garg et al. CAV 2014 and POPL 2016, and Padhi et al. PLDI 2016

 *

 * This module mantains a set of functions-to-synthesize and a set of term

 * enumerators. When new terms are enumerated it tries to learn new candidate

 * solutions, which are verified outside this module. If verification fails a

 * refinement lemma is generated, which this module sends to the utility that

 * learns candidates.

 */

class CegisUnif : public Cegis

{

 public:

  CegisUnif(QuantifiersState& qs,

            QuantifiersInferenceManager& qim,

            TermDbSygus* tds,

            SynthConjecture* p);

  ~CegisUnif() override;

  /** Retrieves enumerators for constructing solutions

   *

   * Non-unification candidates have themselves as enumerators, while for

   * unification candidates we add their conditonal enumerators to enums if

   * their respective guards are set in the current model

   */

  void getTermList(const std::vector<Node>& candidates,

                   std::vector<Node>& enums) override;

  /** Communicates refinement lemma to unification utility and external modules

   *

   * For the lemma to be sent to the external modules it adds a guard from the

   * parent conjecture which establishes that if the conjecture has a solution

   * then it must satisfy this refinement lemma

   *

   * For the lemma to be sent to the unification utility it purifies the

   * arguments of the function-to-synthensize such that all of its applications

   * are over concrete values. E.g.:

   *   f(f(f(0))) > 1

   * becomes

   *   f(0) != c1 v f(c1) != c2 v f(c2) > 1

   * in which c1 and c2 are concrete integer values

   *

   * Note that the lemma is in the deep embedding, which means that the above

   * example would actually correspond to

   *   eval(d, 0) != c1 v eval(d, c1) != c2 v eval(d, c2) > 1

   * in which d is the deep embedding of the function-to-synthesize f

   */

  void registerRefinementLemma(const std::vector<Node>& vars,

                               Node lem,

                               std::vector<Node>& lems) override;

 private:

  /** do cegis-implementation-specific initialization for this class */

  bool processInitialize(Node conj,

                         Node n,

                         const std::vector<Node>& candidates,

                         std::vector<Node>& lemmas) override;

  /** Tries to build new candidate solutions with new enumerated expressions

   *

   * This function relies on a data-driven unification-based approach for

   * constructing solutions for the functions-to-synthesize. See SygusUnifRl for

   * more details.

   *

   * Calls to this function are such that terms is the list of active

   * enumerators (returned by getTermList), and term_values are their current

   * model values. This function registers { terms -> terms_values } in

   * the database of values that have been enumerated, which are in turn used

   * for constructing candidate solutions when possible.

   *

   * This function also excludes models where (terms = terms_values) by adding

   * blocking clauses to lems. For example, for grammar:

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

   * and a call where terms = { d } and term_values = { +( x, 1 ) }, it adds:

   *   ~G V ~is_+( d ) V ~is_x( d.1 ) V ~is_1( d.2 )

   * to lems, where G is active guard of the enumerator d (see

   * TermDatabaseSygus::getActiveGuardForEnumerator). This blocking clause

   * indicates that d should not be given the model value +( x, 1 ) anymore,

   * since { d -> +( x, 1 ) } has now been added to the database of this class.

   */

  bool processConstructCandidates(const std::vector<Node>& enums,

                                  const std::vector<Node>& enum_values,

                                  const std::vector<Node>& candidates,

                                  std::vector<Node>& candidate_values,

                                  bool satisfiedRl,

                                  std::vector<Node>& lems) override;

  /** communicate condition values to solution building utility

   *

   * for each unification candidate and for each strategy point associated with

   * it, set in d_sygus_unif the condition values (unif_cvalues) for respective

   * condition enumerators (unif_cenums)

   */

  void setConditions(const std::map<Node, std::vector<Node>>& unif_cenums,

                     const std::map<Node, std::vector<Node>>& unif_cvalues,

                     std::vector<Node>& lems);

  /** set values of condition enumerators based on current enumerator assignment

   *

   * enums and enum_values are the enumerators registered in getTermList and

   * their values retrieved by the parent SynthConjecture module, respectively.

   *

   * unif_cenums and unif_cvalues associate the conditional enumerators of each

   * strategy point of each unification candidate with their respective model

   * values

   *

   * This function also generates inter-enumerator symmetry breaking for return

   * values, such that their model values are ordered by size

   *

   * returns true if no symmetry breaking lemmas were generated for the return

   * value enumerators, false otherwise

   */

  bool getEnumValues(const std::vector<Node>& enums,

                     const std::vector<Node>& enum_values,

                     std::map<Node, std::vector<Node>>& unif_cenums,

                     std::map<Node, std::vector<Node>>& unif_cvalues,

                     std::vector<Node>& lems);

  /**

   * Whether we are using condition pool enumeration (Section 4 of Barbosa et al

   * FMCAD 2019). This is determined by option::sygusUnifPi().

   */

  bool usingConditionPool() const;

  /**

   * Sygus unif utility. This class implements the core algorithm (e.g. decision

   * tree learning) that this module relies upon.

   */

  SygusUnifRl d_sygus_unif;

  /** enumerator manager utility */

  CegisUnifEnumDecisionStrategy d_u_enum_manager;

  /* The null node */

  Node d_null;

  /** the unification candidates */

  std::vector<Node> d_unif_candidates;

  /** the non-unification candidates */

  std::vector<Node> d_non_unif_candidates;

  /** list of strategy points per candidate */

  std::map<Node, std::vector<Node>> d_cand_to_strat_pt;

  /** map from conditional enumerators to their strategy point */

  std::map<Node, Node> d_cenum_to_strat_pt;

}; /* class CegisUnif */

}  // namespace quantifiers

}  // namespace theory

}  // namespace cvc5

#endif