// Copyright 2016 Google Inc. All rights reserved.
//
// 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 SRC_MUTATOR_H_
#define SRC_MUTATOR_H_

#include <stddef.h>
#include <stdint.h>

#include <functional>
#include <memory>
#include <random>
#include <string>
#include <unordered_map>
#include <vector>

#include "port/protobuf.h"
#include "src/random.h"

namespace protobuf_mutator {

// Randomly makes incremental change in the given protobuf.
// Usage example:
//    protobuf_mutator::Mutator mutator(1);
//    MyMessage message;
//    message.ParseFromString(encoded_message);
//    mutator.Mutate(&message, 10000);
//
// Class implements very basic mutations of fields. E.g. it just flips bits for
// integers, floats and strings. Also it increases, decreases size of
// strings only by one. For better results users should override
// protobuf_mutator::Mutator::Mutate* methods with more useful logic, e.g. using
// library like libFuzzer.
class Mutator {
 public:
  // seed: value to initialize random number generator.
  explicit Mutator(RandomEngine* random);
  virtual ~Mutator() = default;

  // message: message to mutate.
  // size_increase_hint: approximate number of bytes which can be added to the
  // message. Method does not guarantee that real result size increase will be
  // less than the value. It only changes probabilities of mutations which can
  // cause size increase. Caller could repeat mutation if result was larger than
  // requested.
  void Mutate(protobuf::Message* message, size_t size_increase_hint);

  void CrossOver(const protobuf::Message& message1,
                 protobuf::Message* message2);

  // field: Descriptor of the field to apply the mutation to.
  // mutation: callback function that applies the mutation.
  static void RegisterCustomMutation(
      const protobuf::FieldDescriptor* field,
      std::function<void(protobuf::Message* message)> mutation);

 protected:
  // TODO(vitalybuka): Consider to replace with single mutate (uint8_t*, size).
  virtual int32_t MutateInt32(int32_t value);
  virtual int64_t MutateInt64(int64_t value);
  virtual uint32_t MutateUInt32(uint32_t value);
  virtual uint64_t MutateUInt64(uint64_t value);
  virtual float MutateFloat(float value);
  virtual double MutateDouble(double value);
  virtual bool MutateBool(bool value);
  virtual size_t MutateEnum(size_t index, size_t item_count);
  virtual std::string MutateString(const std::string& value,
                                   size_t size_increase_hint);

  // TODO(vitalybuka): Allow user to control proto level mutations:
  //   * Callbacks to recursive traversal.
  //   * Callbacks for particular proto level mutations.

  RandomEngine* random() { return random_; }

  static std::unordered_map<
      const protobuf::FieldDescriptor*,
      std::vector<std::function<void(protobuf::Message* message)>>>
      custom_mutations_;

 private:
  friend class FieldMutator;
  friend class TestMutator;
  void InitializeAndTrim(protobuf::Message* message, int max_depth);
  void CrossOverImpl(const protobuf::Message& message1,
                     protobuf::Message* message2);
  std::string MutateUtf8String(const std::string& value,
                               size_t size_increase_hint);
  bool ApplyCustomMutations(protobuf::Message* message,
                            const protobuf::FieldDescriptor* field);
  bool keep_initialized_ = true;
  RandomEngine* random_;
};

}  // namespace protobuf_mutator

#endif  // SRC_MUTATOR_H_