#include "arch/memory/paging.hpp"

#include "arch/exception_handling/assert.hpp"

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

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

  auto entry::calculate_pointed_to_frame() const -> std::optional<physical_frame>
  {
    if (contains_flags(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 = 52U;
    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::contains_flags(std::bitset<64U> b) const -> bool { return (flags & b) == b; }

  auto entry::set_address(physical_frame frame) -> void
  {
    arch::exception_handling::assert((frame.start_address() & ~0x000fffff'fffff000) == 0,
                                     "Start address is not aligned with Page");
    flags = std::bitset<64U>(frame.start_address()) | flags;
  }

  auto page_table::zero_entries() -> void
  {
    auto begin = &entries[0];
    auto end = &entries[PAGE_TABLE_ENTRY_COUNT];

    for (auto entry = begin; entry < end; ++entry)
    {
      entry->set_unused();
    }
  }
}  // namespace teachos::arch::memory