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

 * Top contributors (to current version):

 *   Andrew Reynolds, Gereon Kremer

 *

 * 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.

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

 *

 * The trust node utility.

 */

#include "cvc5_private.h"

#ifndef CVC5__PROOF__TRUST_NODE_H

#define CVC5__PROOF__TRUST_NODE_H

#include "expr/node.h"

namespace cvc5 {

class ProofGenerator;

class ProofNode;

/** A kind for trust nodes */

enum class TrustNodeKind : uint32_t

{

  CONFLICT,

  LEMMA,

  PROP_EXP,

  REWRITE,

  INVALID

};

/**

 * Converts a proof rule to a string. Note: This function is also used in

 * `safe_print()`. Changing this function name or signature will result in

 * `safe_print()` printing "<unsupported>" instead of the proper strings for

 * the enum values.

 *

 * Returns a string with static lifetime: it should not be freed.

 *

 * @param tnk The trust node kind

 * @return The name of the trust node kind

 */

const char* toString(TrustNodeKind tnk);

/**

 * Writes a trust node kind name to a stream.

 *

 * @param out The stream to write to

 * @param tnk The trust node kind to write to the stream

 * @return The stream

 */

std::ostream& operator<<(std::ostream& out, TrustNodeKind tnk);

/**

 * A trust node is a pair (F, G) where F is a formula and G is a proof

 * generator that can construct a proof for F if asked.

 *

 * More generally, a trust node is any node that can be used for a specific

 * purpose that requires justification, such as being passed to

 * OutputChannel::lemma. That justification is intended to be given by the

 * generator that is required to construct this object.

 *

 * They are intended to be constructed by ProofGenerator objects themselves (a

 * proof generator wraps itself in TrustNode it returns) and passed

 * to ProofOutputChannel by theory solvers.

 *

 * The static functions for constructing them check that the generator, if

 * provided, is capable of proving the given conflict or lemma, or an assertion

 * failure occurs. Otherwise an assertion error is given.

 *

 * While this is not enforced, a `TrustNode` generally encapsulates a **closed**

 * proof of the formula: one without free assumptions.

 */

{

 public:

  /** Make a proven node for conflict */

  static TrustNode mkTrustConflict(Node conf, ProofGenerator* g = nullptr);

  /** Make a proven node for lemma */

  static TrustNode mkTrustLemma(Node lem, ProofGenerator* g = nullptr);

  /** Make a proven node for explanation of propagated literal */

  static TrustNode mkTrustPropExp(TNode lit,

                                  Node exp,

                                  ProofGenerator* g = nullptr);

  /** Make a proven node for rewrite */

  static TrustNode mkTrustRewrite(TNode n,

                                  Node nr,

                                  ProofGenerator* g = nullptr);

  /** The null proven node */

  static TrustNode null();

  /** get kind */

  TrustNodeKind getKind() const;

  /** get node

   *

   * This is the node that is used in a common interface, either:

   * (1) A T-unsat conjunction conf to pass to OutputChannel::conflict,

   * (2) A valid T-formula lem to pass to OutputChannel::lemma,

   * (3) A conjunction of literals exp to return in Theory::explain(lit), or

   * (4) A result of rewriting a term n into an equivalent one nr.

   *

   * Notice that this node does not necessarily correspond to a valid formula.

   * The call getProven() below retrieves a valid formula corresponding to

   * the above calls.

   */

  Node getNode() const;

  /** get proven

   *

   * This is the corresponding formula that is proven by the proof generator

   * for the above cases:

   * (1) (not conf), for conflicts,

   * (2) lem, for lemmas,

   * (3) (=> exp lit), for propagations from explanations,

   * (4) (= n nr), for results of rewriting.

   *

   * When constructing this trust node, the proof generator should be able to

   * provide a proof for this fact.

   */

  Node getProven() const;

  /** get generator */

  ProofGenerator* getGenerator() const;

  /** is null? */

  bool isNull() const;

  /**

   * Gets the proof node for this trust node, which is obtained by

   * calling the generator's getProofFor method on the proven node.

   */

  std::shared_ptr<ProofNode> toProofNode() const;

  /** Get the proven formula corresponding to a conflict call */

  static Node getConflictProven(Node conf);

  /** Get the proven formula corresponding to a lemma call */

  static Node getLemmaProven(Node lem);

  /** Get the proven formula corresponding to explanations for propagation */

  static Node getPropExpProven(TNode lit, Node exp);

  /** Get the proven formula corresponding to a rewrite */

  static Node getRewriteProven(TNode n, Node nr);

  /** For debugging */

  std::string identifyGenerator() const;

  /**

   * debug check closed on Trace c, context ctx is string for debugging

   *

   * @param reqNullGen Whether we consider a null generator to be a failure.

   */

  void debugCheckClosed(const char* c, const char* ctx, bool reqNullGen = true);

 private:

  TrustNode(TrustNodeKind tnk, Node p, ProofGenerator* g = nullptr);

  /** The kind */

  TrustNodeKind d_tnk;

  /** The proven node */

  Node d_proven;

  /** The generator */

  ProofGenerator* d_gen;

};

/**

 * Writes a trust node to a stream.

 *

 * @param out The stream to write to

 * @param n The trust node to write to the stream

 * @return The stream

 */

std::ostream& operator<<(std::ostream& out, TrustNode n);

}  // namespace cvc5

#endif /* CVC5__PROOF__TRUST_NODE_H */