// Copyright 2021 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef FUZZERS_TINT_AST_FUZZER_MUTATION_H_
#define FUZZERS_TINT_AST_FUZZER_MUTATION_H_

#include <memory>
#include <vector>

#include "fuzzers/tint_ast_fuzzer/node_id_map.h"
#include "fuzzers/tint_ast_fuzzer/protobufs/tint_ast_fuzzer.h"

#include "src/clone_context.h"
#include "src/program.h"

namespace tint {
namespace fuzzers {
namespace ast_fuzzer {

/// The base class for all the mutations in the fuzzer. Children must override
/// three methods:
/// - `IsApplicable` - checks whether it is possible to apply the mutation
///   in a manner that will lead to a valid program.
/// - `Apply` - applies the mutation.
/// - `ToMessage` - converts the mutation data into a protobuf message.
class Mutation {
 public:
  /// Virtual destructor.
  virtual ~Mutation();

  /// @brief Determines whether this mutation is applicable to the `program`.
  ///
  /// @param program - the program this mutation will be applied to. The program
  ///     must be valid.
  /// @param node_id_map - the map from `tint::ast::` nodes to their ids.
  /// @return `true` if `Apply` method can be called without breaking the
  ///     semantics of the `program`.
  /// @return `false` otherwise.
  virtual bool IsApplicable(const tint::Program& program,
                            const NodeIdMap& node_id_map) const = 0;

  /// @brief Applies this mutation to the `clone_context`.
  ///
  /// Precondition: `IsApplicable` must return `true` when invoked on the same
  /// `node_id_map` and `clone_context->src` instance of `tint::Program`. A new
  /// `tint::Program` that arises in `clone_context` must be valid.
  ///
  /// @param node_id_map - the map from `tint::ast::` nodes to their ids.
  /// @param clone_context - the context that will clone the program with some
  ///     changes introduced by this mutation.
  /// @param new_node_id_map - this map will store ids for the mutated and
  ///     cloned program. This argument cannot be a `nullptr` nor can it point
  ///     to the same object as `node_id_map`.
  virtual void Apply(const NodeIdMap& node_id_map,
                     tint::CloneContext* clone_context,
                     NodeIdMap* new_node_id_map) const = 0;

  /// @return a protobuf message for this mutation.
  virtual protobufs::Mutation ToMessage() const = 0;

  /// @brief Converts a protobuf message into the mutation instance.
  ///
  /// @param message - a protobuf message.
  /// @return the instance of this class.
  static std::unique_ptr<Mutation> FromMessage(
      const protobufs::Mutation& message);
};

using MutationList = std::vector<std::unique_ptr<Mutation>>;

}  // namespace ast_fuzzer
}  // namespace fuzzers
}  // namespace tint

#endif  // FUZZERS_TINT_AST_FUZZER_MUTATION_H_