#include "arch/memory/paging.hpp"

namespace teachos::arch::memory
{
  auto entry::is_unused() const -> bool { return flags == 0U; }

  auto entry::set_unused() -> void { flags = 0U; }

  auto entry::present() const -> bool { return is_bit_set(0U); }

  auto entry::writable() const -> bool { return is_bit_set(1U); }

  auto entry::user_accessible() const -> bool { return is_bit_set(2U); }

  auto entry::write_through_caching() const -> bool { return is_bit_set(3U); }

  auto entry::disabled_caching() const -> bool { return is_bit_set(4U); }

  auto entry::is_accessing() const -> bool { return is_bit_set(5U); }

  auto entry::is_diry() const -> bool { return is_bit_set(6U); }

  auto entry::is_huge_page() const -> bool { return is_bit_set(7U); }

  auto entry::is_global() const -> bool { return is_bit_set(8U); }

  auto entry::executing_code_forbidden() const -> bool { return is_bit_set(63U); }

  auto entry::calculate_pointed_to_frame() const -> std::optional<physical_frame>
  {
    if (present())
    {
      auto physical_address = calculate_physical_address();
      return physical_frame::containing_address(physical_address);
    }
    return std::nullopt;
  }

  auto entry::calculate_physical_address() const -> std::size_t
  {
    constexpr std::size_t start_bit = 12U;
    constexpr std::size_t end_bit = 51U;
    size_t value = 0U;

    for (auto i = start_bit; i < end_bit; i++)
    {
      value |= (flags[i] ? (1 << (i - start_bit)) : 0);
    }
    return value;
  }

  auto entry::is_bit_set(uint8_t index) const -> bool { return flags[index] == 1U; }
}  // namespace teachos::arch::memory