#include <algorithm>

#include <cassert>

#include <cstdlib>

#include <type_traits>

#include <vector>

#include "simdutf.h"

void test_latin1_to_utf8(std::span<const uint8_t> input_bytes,

                         std::size_t output_size) {

  std::vector<char> output(output_size);

  const auto written_bytes_safe =

      simdutf::convert_latin1_to_utf8_safe(input_bytes, output);

  if (written_bytes_safe > output_size) {

    std::abort();

  }

  const auto needed_size = simdutf::utf8_length_from_latin1(input_bytes);

  std::vector<char> reference(needed_size);

  const auto written_bytes_unsafe =

      simdutf::convert_latin1_to_utf8(input_bytes, reference);

  if (written_bytes_unsafe != needed_size) {

    std::abort();

  }

  if (written_bytes_safe > needed_size) {

    // convert_latin1_to_utf8_safe wrote more output buffer than the unsafe

    // version needed!

    std::abort();

  }

  // ensure output is equal to the beginning of reference

  if (!std::ranges::equal(

          std::span(output).subspan(0, written_bytes_safe),

          std::span(reference).subspan(0, written_bytes_safe))) {

    std::abort();

  }

}

void test_utf16_to_utf8(std::span<const char16_t> input,

                        std::size_t output_size) {

  std::vector<char> output(output_size);

  const auto written_bytes_safe =

      simdutf::convert_utf16_to_utf8_safe(input, output);

  if (written_bytes_safe > output_size) {

    std::abort();

  }

  // result is implementation defined in case of garbage input

  const auto unreliable_needed_size = simdutf::utf8_length_from_utf16(input);

  std::vector<char> reference(unreliable_needed_size);

  const auto written_bytes_unsafe =

      simdutf::convert_utf16_to_utf8(input, reference);

  // ensure output is equal to the beginning of reference

  const auto Ncompare =

      simdutf::detail::min(written_bytes_safe, written_bytes_unsafe);

  const auto matches =

      std::ranges::equal(std::span(output).subspan(0, Ncompare),

                         std::span(reference).subspan(0, Ncompare));

  assert(matches);

  if (!matches) {

    std::abort();

  }

}

void select_implementation(auto index) {

  static const auto implementations = []() {

    const auto list = simdutf::get_available_implementations();

    using Impl = std::decay_t<decltype(*list.begin())>;

    std::vector<Impl> ret;

    for (auto& e : list) {

      if (e->supported_by_runtime_system()) {

        ret.push_back(e);

      }

    }

    return ret;

  }();

  assert(!implementations.empty());

  simdutf::get_active_implementation() =

      implementations.at(index % implementations.size());

}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {

  if (size < 4) {

    return 0;

  }

  const auto action = data[0] & 0x1;

  const auto output_size = (data[1] << 8 | data[2]);

  const auto implementation_index = data[3] & 0b0111;

  data += 4;

  size -= 4;

  const std::span<const uint8_t> input_bytes{data, data + size};

  select_implementation(implementation_index);

  switch (action) {

  case 0:

    test_latin1_to_utf8(input_bytes, output_size);

    break;

  case 1: {

    const auto* ptr = reinterpret_cast<const char16_t*>(input_bytes.data());

    test_utf16_to_utf8(std::span(ptr, ptr + input_bytes.size() / 2),

                       output_size);

  } break;

  }

  return 0;

}