// Copyright 2022 Google LLC
//
// 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 FUZZTEST_FUZZTEST_INTERNAL_DOMAINS_ARBITRARY_IMPL_H_
#define FUZZTEST_FUZZTEST_INTERNAL_DOMAINS_ARBITRARY_IMPL_H_

#include <array>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <memory>
#include <optional>
#include <string_view>
#include <tuple>
#include <type_traits>
#include <utility>
#include <variant>
#include <vector>

#include "absl/random/bit_gen_ref.h"
#include "absl/random/distributions.h"
#include "absl/strings/string_view.h"
#include "absl/time/time.h"
#include "./fuzztest/internal/coverage.h"
#include "./fuzztest/internal/domains/absl_helpers.h"
#include "./fuzztest/internal/domains/aggregate_of_impl.h"
#include "./fuzztest/internal/domains/container_of_impl.h"
#include "./fuzztest/internal/domains/domain.h"
#include "./fuzztest/internal/domains/domain_base.h"
#include "./fuzztest/internal/domains/element_of_impl.h"
#include "./fuzztest/internal/domains/in_range_impl.h"
#include "./fuzztest/internal/domains/map_impl.h"
#include "./fuzztest/internal/domains/one_of_impl.h"
#include "./fuzztest/internal/domains/optional_of_impl.h"
#include "./fuzztest/internal/domains/smart_pointer_of_impl.h"
#include "./fuzztest/internal/domains/value_mutation_helpers.h"
#include "./fuzztest/internal/domains/variant_of_impl.h"
#include "./fuzztest/internal/meta.h"
#include "./fuzztest/internal/serialization.h"
#include "./fuzztest/internal/status.h"
#include "./fuzztest/internal/table_of_recent_compares.h"
#include "./fuzztest/internal/type_support.h"

namespace fuzztest::internal {

// Fallback for error reporting, if T is not matched in Arbitrary<T>.
template <typename T, typename = void>
class ArbitraryImpl {
  static_assert(always_false<T>,
                "=> Type not supported yet. Consider filing an issue."
  );
};

// Arbitrary for monostate.
//
// For monostate types with a default constructor, just give the single value.
template <typename T>
class ArbitraryImpl<T, std::enable_if_t<is_monostate_v<T>>>
    : public domain_implementor::DomainBase<ArbitraryImpl<T>> {
 public:
  using typename ArbitraryImpl::DomainBase::value_type;

  value_type Init(absl::BitGenRef) { return value_type{}; }

  void Mutate(value_type&, absl::BitGenRef, bool) {}

  value_type GetRandomCorpusValue(absl::BitGenRef prng) { return value_type{}; }

  absl::Status ValidateCorpusValue(const value_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

  auto GetPrinter() const { return MonostatePrinter{}; }
};

// Arbitrary for bool.
template <>
class ArbitraryImpl<bool>
    : public domain_implementor::DomainBase<ArbitraryImpl<bool>> {
 public:
  value_type Init(absl::BitGenRef prng) {
    if (auto seed = MaybeGetRandomSeed(prng)) return *seed;
    return static_cast<bool>(absl::Uniform(prng, 0, 2));
  }

  void Mutate(value_type& val, absl::BitGenRef, bool only_shrink) {
    if (only_shrink) {
      val = false;
    } else {
      val = !val;
    }
  }

  value_type GetRandomCorpusValue(absl::BitGenRef prng) { return Init(prng); }

  absl::Status ValidateCorpusValue(const value_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

  auto GetPrinter() const { return IntegralPrinter{}; }
};

// Arbitrary for integers.
template <typename T>
class ArbitraryImpl<T, std::enable_if_t<!std::is_const_v<T> &&
                                        std::numeric_limits<T>::is_integer>>
    : public domain_implementor::DomainBase<ArbitraryImpl<T>> {
 public:
  using typename ArbitraryImpl::DomainBase::value_type;

  static constexpr bool is_memory_dictionary_compatible_v =
      sizeof(T) == 1 || sizeof(T) == 2 || sizeof(T) == 4 || sizeof(T) == 8;
  using IntegerDictionaryT =
      std::conditional_t<is_memory_dictionary_compatible_v,
                         IntegerDictionary<T>, bool>;

  value_type Init(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    if constexpr (sizeof(T) == 1) {
      return ChooseFromAll(prng);
    } else {
      static constexpr T special[] = {
          T{0}, T{1},
          // For some types, ~T{} is promoted to int. Convert back to T.
          static_cast<T>(~T{}),
          std::numeric_limits<T>::is_signed
              ? std::numeric_limits<T>::max()
              : std::numeric_limits<T>::max() >> 1};
      return ChooseOneOr(special, prng, [&] { return ChooseFromAll(prng); });
    }
  }

  void Mutate(value_type& val, absl::BitGenRef prng, bool only_shrink) {
    permanent_dict_candidate_ = std::nullopt;
    if (only_shrink) {
      if (val == 0) return;
      val = ShrinkTowards(prng, val, T{0});
      return;
    }
    const T prev = val;
    do {
      // Randomly apply 4 kinds of mutations with equal probabilities.
      // Use permanent_dictionary_ or temporary_dictionary_ with equal
      // probabilities.
      if (absl::Bernoulli(prng, 0.25)) {
        RandomBitFlip(prng, val, sizeof(T) * 8);
      } else {
        RandomWalkOrUniformOrDict<5>(prng, val, std::numeric_limits<T>::min(),
                                     std::numeric_limits<T>::max(),
                                     temporary_dict_, permanent_dict_,
                                     permanent_dict_candidate_);
      }
      // Make sure Mutate really mutates.
    } while (val == prev);
  }

  value_type GetRandomCorpusValue(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    return ChooseFromAll(prng);
  }

  void UpdateMemoryDictionary(const value_type& val) {
    if constexpr (is_memory_dictionary_compatible_v) {
      if (GetExecutionCoverage() != nullptr) {
        temporary_dict_.MatchEntriesFromTableOfRecentCompares(
            val, GetExecutionCoverage()->GetTablesOfRecentCompares(),
            std::numeric_limits<T>::min(), std::numeric_limits<T>::max());
        if (permanent_dict_candidate_.has_value() &&
            permanent_dict_.Size() < kPermanentDictMaxSize) {
          permanent_dict_.AddEntry(std::move(*permanent_dict_candidate_));
          permanent_dict_candidate_ = std::nullopt;
        }
      }
    }
  }

  absl::Status ValidateCorpusValue(const value_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

  auto GetPrinter() const { return IntegralPrinter{}; }

 private:
  static value_type ChooseFromAll(absl::BitGenRef prng) {
    return absl::Uniform(absl::IntervalClosedClosed, prng,
                         std::numeric_limits<T>::min(),
                         std::numeric_limits<T>::max());
  }

  // Matched snapshots from table of recent compares.
  // It's the "unverified" dictionary entries: the mutated
  // value matched something in this snapshot, but not sure
  // if it will lead to new coverage.
  IntegerDictionaryT temporary_dict_;
  // Set of dictionary entries from previous `temporary_dict_`
  // that leads to new coverage. This is based on a heuristic
  // that such entries may lead to interesting behaviors even
  // after the first new coverage it triggered.
  IntegerDictionaryT permanent_dict_;
  std::optional<T> permanent_dict_candidate_;
  static constexpr size_t kPermanentDictMaxSize = 512;
};

// Arbitrary for std::byte.
template <>
class ArbitraryImpl<std::byte>
    : public domain_implementor::DomainBase<ArbitraryImpl<std::byte>> {
 public:
  using typename ArbitraryImpl::DomainBase::corpus_type;
  using typename ArbitraryImpl::DomainBase::value_type;

  value_type Init(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    return std::byte{inner_.Init(prng)};
  }

  void Mutate(corpus_type& val, absl::BitGenRef prng, bool only_shrink) {
    unsigned char u8 = std::to_integer<unsigned char>(val);
    inner_.Mutate(u8, prng, only_shrink);
    val = std::byte{u8};
  }

  value_type GetRandomCorpusValue(absl::BitGenRef prng) { return Init(prng); }

  absl::Status ValidateCorpusValue(const corpus_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

  auto GetPrinter() const { return IntegralPrinter{}; }

 private:
  ArbitraryImpl<unsigned char> inner_;
};

// Arbitrary for floats.
template <typename T>
class ArbitraryImpl<T, std::enable_if_t<std::is_floating_point_v<T>>>
    : public domain_implementor::DomainBase<ArbitraryImpl<T>> {
 public:
  using typename ArbitraryImpl::DomainBase::value_type;

  value_type Init(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    const T special[] = {
        T{0.0}, T{-0.0}, T{1.0}, T{-1.0}, std::numeric_limits<T>::max(),
        std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity(),
        // std::nan is double. Cast to T explicitly.
        static_cast<T>(std::nan(""))};
    return ChooseOneOr(special, prng,
                       [&] { return absl::Uniform(prng, T{0}, T{1}); });
  }

  void Mutate(value_type& val, absl::BitGenRef prng, bool only_shrink) {
    if (only_shrink) {
      if (!std::isfinite(val) || val == 0) return;
      val = ShrinkTowards(prng, val, T{0});
      return;
    }
    const T prev = val;
    do {
      // If it is not finite we can't change it a bit because it would stay the
      // same. eg inf/2 == inf.
      if (!std::isfinite(val)) {
        val = Init(prng);
      } else {
        RunOne(
            prng,                    //
            [&] { val = val / 2; },  //
            [&] { val = -val; },     //
            [&] { val = val + 1; },  //
            [&] { val = val * 3; });
      }

      // Make sure Mutate really mutates.
    } while (val == prev || (std::isnan(prev) && std::isnan(val)));
  }

  absl::Status ValidateCorpusValue(const value_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

  auto GetPrinter() const { return FloatingPrinter{}; }
};

// Arbitrary for containers.
template <typename T>
class ArbitraryImpl<
    T,
    std::enable_if_t<always_true<T>,
                     decltype(
                         // Iterable
                         T().begin(), T().end(), T().size(),
                         // Values are mutable
                         // This rejects associative containers, for example
                         // *T().begin() = std::declval<value_type_t<T>>(),
                         // Can insert and erase elements
                         T().insert(T().end(), std::declval<value_type_t<T>>()),
                         T().erase(T().begin()),
                         //
                         (void)0)>>
    : public ContainerOfImpl<T, ArbitraryImpl<value_type_t<T>>> {};

// Arbitrary for std::string_view.
//
// We define a separate container for string_view, to detect out of bounds bugs
// better. See below.
template <typename Char>
class ArbitraryImpl<std::basic_string_view<Char>>
    : public domain_implementor::DomainBase<
          ArbitraryImpl<std::basic_string_view<Char>>,
          std::basic_string_view<Char>,
          // We use a vector to better manage the buffer and help
          // ASan find out-of-bounds bugs.
          std::vector<Char>> {
 public:
  using typename ArbitraryImpl::DomainBase::corpus_type;
  using typename ArbitraryImpl::DomainBase::value_type;

  corpus_type Init(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    return inner_.Init(prng);
  }

  void Mutate(corpus_type& val, absl::BitGenRef prng, bool only_shrink) {
    inner_.Mutate(val, prng, only_shrink);
  }

  void UpdateMemoryDictionary(const corpus_type& val) {
    inner_.UpdateMemoryDictionary(val);
  }

  auto GetPrinter() const { return StringPrinter{}; }

  value_type GetValue(const corpus_type& value) const {
    return value_type(value.data(), value.size());
  }

  std::optional<corpus_type> FromValue(const value_type& value) const {
    return corpus_type(value.begin(), value.end());
  }

  std::optional<corpus_type> ParseCorpus(const IRObject& obj) const {
    return obj.ToCorpus<corpus_type>();
  }

  IRObject SerializeCorpus(const corpus_type& v) const {
    return IRObject::FromCorpus(v);
  }

  absl::Status ValidateCorpusValue(const corpus_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

 private:
  ArbitraryImpl<std::vector<Char>> inner_;
};

#ifndef ABSL_USES_STD_STRING_VIEW
// Arbitrary for absl::string_view when it does not alias to std::string_view.
//
// We define a separate container for string_view, to detect out of bounds bugs
// better. See below.
template <>
class ArbitraryImpl<absl::string_view>
    : public domain_implementor::DomainBase<
          ArbitraryImpl<absl::string_view>, absl::string_view,
          // We use a vector to better manage the buffer and help
          // ASan find out-of-bounds bugs.
          std::vector<char>> {
 public:
  using typename ArbitraryImpl::DomainBase::corpus_type;
  using typename ArbitraryImpl::DomainBase::value_type;

  corpus_type Init(absl::BitGenRef prng) {
    if (auto seed = this->MaybeGetRandomSeed(prng)) return *seed;
    return inner_.Init(prng);
  }

  void Mutate(corpus_type& val, absl::BitGenRef prng, bool only_shrink) {
    inner_.Mutate(val, prng, only_shrink);
  }

  void UpdateMemoryDictionary(const corpus_type& val) {
    inner_.UpdateMemoryDictionary(val);
  }

  auto GetPrinter() const { return StringPrinter{}; }

  value_type GetValue(const corpus_type& value) const {
    return value_type(value.data(), value.size());
  }

  std::optional<corpus_type> FromValue(const value_type& value) const {
    return corpus_type(value.begin(), value.end());
  }

  std::optional<corpus_type> ParseCorpus(const IRObject& obj) const {
    return obj.ToCorpus<corpus_type>();
  }

  IRObject SerializeCorpus(const corpus_type& v) const {
    return IRObject::FromCorpus(v);
  }

  absl::Status ValidateCorpusValue(const corpus_type&) const {
    return absl::OkStatus();  // Nothing to validate.
  }

 private:
  ArbitraryImpl<std::vector<char>> inner_;
};
#endif

// Arbitrary for any const T.
//
// We capture const types as a workaround in order to enable
// Arbitrary<std::map<std::string, int>>() and similar container domains that
// require Arbitrary<std::pair< _const_ std::string, int>>() to be defined,
// which in turn requires Arbitrary<const std::string>() to be defined.
template <typename T>
class ArbitraryImpl<const T> : public ArbitraryImpl<T> {};

// Arbitrary for user-defined aggregate types (structs/classes).

template <typename T, typename... Elem>
AggregateOfImpl<T, RequireCustomCorpusType::kYes, ArbitraryImpl<Elem>...>
    DetectAggregateOfImpl2(std::tuple<Elem&...>);

// Detect the number and types of the fields.
// TODO(sbenzaquen): Verify the compiler error in case we can't detect it and
// improve if possible.
template <typename T, int N = *DetectBindableFieldCount<T>()>
decltype(DetectAggregateOfImpl2<T>(
    BindAggregate(std::declval<T&>(), std::integral_constant<int, N>{})))
DetectAggregateOfImpl();

template <typename T>
class ArbitraryImpl<
    T, std::enable_if_t<std::is_class_v<T> && std::is_aggregate_v<T> &&
                        // Monostates have their own domain.
                        !is_monostate_v<T> &&
                        // std::array uses the Tuple domain.
                        !is_array_v<T>>>
    : public decltype(DetectAggregateOfImpl<T>()) {};

// Arbitrary for std::pair.
template <typename T, typename U>
class ArbitraryImpl<std::pair<T, U>>
    : public AggregateOfImpl<
          std::pair<std::remove_const_t<T>, std::remove_const_t<U>>,
          std::is_const_v<T> || std::is_const_v<U>
              ? RequireCustomCorpusType::kYes
              : RequireCustomCorpusType::kNo,
          ArbitraryImpl<T>, ArbitraryImpl<U>> {};

// Arbitrary for std::tuple.
template <typename... T>
class ArbitraryImpl<std::tuple<T...>, std::enable_if_t<sizeof...(T) != 0>>
    : public AggregateOfImpl<std::tuple<T...>, RequireCustomCorpusType::kNo,
                             ArbitraryImpl<T>...> {};

// Arbitrary for std::array.
template <typename T, size_t N>
auto AggregateOfImplForArray() {
  return ApplyIndex<N>([&](auto... I) {
    return AggregateOfImpl<std::array<T, N>, RequireCustomCorpusType::kNo,
                           std::enable_if_t<(I >= 0), ArbitraryImpl<T>>...>{};
  });
}
template <typename T, size_t N>
class ArbitraryImpl<std::array<T, N>>
    : public decltype(AggregateOfImplForArray<T, N>()) {};

// Arbitrary for std::variant.
template <typename... T>
class ArbitraryImpl<std::variant<T...>>
    : public VariantOfImpl<std::variant<T...>, ArbitraryImpl<T>...> {};

// Arbitrary for std::optional.
template <typename T>
class ArbitraryImpl<std::optional<T>>
    : public OptionalOfImpl<std::optional<T>> {
 public:
  ArbitraryImpl() : ArbitraryImpl::OptionalOfImpl(ArbitraryImpl<T>()) {}
};

// Used by Arbitrary std::unique_ptr / std::shared_ptr.
template <typename T>
const Domain<T>& GetGlobalDomainDefaultInstance() {
  static const auto* instance = new Domain<T>(ArbitraryImpl<T>());
  return *instance;
}

// Arbitrary for std::unique_ptr.
template <typename T>
class ArbitraryImpl<std::unique_ptr<T>>
    : public SmartPointerOfImpl<std::unique_ptr<T>> {
 public:
  ArbitraryImpl()
      : ArbitraryImpl::SmartPointerOfImpl(GetGlobalDomainDefaultInstance) {}
};

// Arbitrary for std::shared_ptr.
template <typename T>
class ArbitraryImpl<std::shared_ptr<T>>
    : public SmartPointerOfImpl<std::shared_ptr<T>> {
 public:
  ArbitraryImpl()
      : ArbitraryImpl::SmartPointerOfImpl(GetGlobalDomainDefaultInstance) {}
};

// Arbitrary for absl::Duration.
template <>
class ArbitraryImpl<absl::Duration>
    : public OneOfImpl<
          ElementOfImpl<absl::Duration>,
          ReversibleMapImpl<absl::Duration (*)(int64_t, uint32_t),
                            std::optional<std::tuple<int64_t, uint32_t>> (*)(
                                absl::Duration),
                            ArbitraryImpl<int64_t>, InRangeImpl<uint32_t>>> {
 public:
  ArbitraryImpl()
      : OneOfImpl(
            ElementOfImpl<absl::Duration>(
                {absl::InfiniteDuration(), -absl::InfiniteDuration()}),
            ReversibleMapImpl<absl::Duration (*)(int64_t, uint32_t),
                              std::optional<std::tuple<int64_t, uint32_t>> (*)(
                                  absl::Duration),
                              ArbitraryImpl<int64_t>, InRangeImpl<uint32_t>>(
                [](int64_t secs, uint32_t ticks) {
                  return MakeDuration(secs, ticks);
                },
                [](absl::Duration duration) {
                  auto [secs, ticks] = GetSecondsAndTicks(duration);
                  return std::optional{std::tuple{secs, ticks}};
                },
                ArbitraryImpl<int64_t>(),
                // ticks is 1/4 of a nanosecond and has a range of [0, 4B - 1]
                InRangeImpl<uint32_t>(0u, 3'999'999'999u))) {}
};

// Arbitrary for absl::Time.
template <>
class ArbitraryImpl<absl::Time>
    : public ReversibleMapImpl<absl::Time (*)(absl::Duration),
                               std::optional<std::tuple<absl::Duration>> (*)(
                                   absl::Time),
                               ArbitraryImpl<absl::Duration>> {
 public:
  ArbitraryImpl()
      : ReversibleMapImpl<absl::Time (*)(absl::Duration),
                          std::optional<std::tuple<absl::Duration>> (*)(
                              absl::Time),
                          ArbitraryImpl<absl::Duration>>(
            [](absl::Duration duration) {
              return absl::UnixEpoch() + duration;
            },
            [](absl::Time time) {
              return std::optional{std::tuple{time - absl::UnixEpoch()}};
            },
            ArbitraryImpl<absl::Duration>()) {}
};

}  // namespace fuzztest::internal

#endif  // FUZZTEST_FUZZTEST_INTERNAL_DOMAINS_ARBITRARY_IMPL_H_
