#include <algorithm>
#include <bit>
#include <cstddef>
#include <iterator>
#include <span>

namespace kstd::libc
{

  extern "C"
  {
    auto strlen(char const * string) -> std::size_t
    {
      return std::distance(string, std::ranges::find(string, nullptr, '\0'));
    }

    auto memcmp(void const * lhs, void const * rhs, std::size_t size) -> std::size_t
    {
      auto left_span = std::span{static_cast<std::byte const *>(lhs), size};
      auto right_span = std::span{static_cast<std::byte const *>(rhs), size};
      auto mismatched = std::ranges::mismatch(left_span, right_span);

      if (mismatched.in1 == left_span.end())
      {
        return 0;
      }

      return std::bit_cast<char>(*mismatched.in1) - std::bit_cast<char>(*mismatched.in2);
    }

    auto memmove(void * dest, void const * src, std::size_t size) -> void *
    {
      auto dest_span = std::span{static_cast<std::byte *>(dest), size};
      auto src_span = std::span{static_cast<std::byte const *>(src), size};
      if (dest < src)
      {
        for (std::size_t i = 0; i < size; ++i)
        {
          dest_span[i] = src_span[i];
        }
      }
      else
      {
        for (std::size_t i = size; i > 0; --i)
        {
          dest_span[i - 1] = src_span[i - 1];
        }
      }
      return dest;
    }
  }

}  // namespace kstd::libc