#include "arch/kernel/main.hpp"

#include "arch/boot/pointers.hpp"
#include "arch/memory/frame_allocator.hpp"
#include "arch/memory/multiboot.hpp"
#include "arch/video/vga/text.hpp"

namespace teachos::arch::kernel
{
  auto assert(bool condition) -> void
  {
    if (condition)
    {
      return;
    }

    video::vga::text::write("Assert failed", video::vga::text::common_attributes::green_on_black);
    for (;;)
    {
      // Trick the compiler into thinking the variable is changes at run time,
      // to prevent the while loop being optimized away
      // See
      // https://stackoverflow.com/questions/9495856/how-to-prevent-g-from-optimizing-out-a-loop-controlled-by-a-variable-that-can
      // for more information.
      asm volatile("" : "+g"(condition));
    }
  }

  auto process_memory_map(arch::memory::memory_map * mminfo, arch::memory::memory_area *& memory_areas,
                          uint8_t & area_count) -> void
  {
    auto expected_entry_size = mminfo->entry_size;
    constexpr auto actual_entry_size = sizeof(arch::memory::memory_area);
    assert(expected_entry_size == actual_entry_size);

    auto total_size = mminfo->tag.size;
    auto total_entries_size = total_size - sizeof(arch::memory::memory_map) + actual_entry_size;
    auto number_of_entries = total_entries_size / actual_entry_size;

    memory_areas = &mminfo->entries;
    area_count = number_of_entries;
  }

  auto process_elf_sections(arch::memory::elf_symbols_section * symbol, uint64_t & kernel_start,
                            uint64_t & kernel_end) -> void
  {
    auto expected_entry_size = symbol->entry_size;
    constexpr auto actual_entry_size = sizeof(arch::memory::elf_section_header);
    assert(expected_entry_size == actual_entry_size);

    auto expected_total_size = symbol->tag.size;
    auto actual_total_entry_size = actual_entry_size * symbol->number_of_sections;
    constexpr auto actual_total_section_size = sizeof(arch::memory::elf_symbols_section) - sizeof(uint32_t);
    auto actual_total_size = actual_total_entry_size + actual_total_section_size;
    assert(expected_total_size == actual_total_size);

    auto begin = reinterpret_cast<arch::memory::elf_section_header *>(&symbol->end);
    auto end = begin + symbol->number_of_sections;
    assert(begin->is_null());

    std::size_t symbol_table_section_count = 0U;
    std::size_t dynamic_section_count = 0U;

    for (auto section = begin; section != end; ++section)
    {
      switch (section->type)
      {
        case arch::memory::elf_section_type::PROGRAMM: {
          if (section->virtual_address < kernel_start)
          {
            kernel_start = section->virtual_address;
          }
          auto virtual_address_end = section->virtual_address + section->section_size;
          if (virtual_address_end > kernel_end)
          {
            kernel_end = virtual_address_end;
          }
          break;
        }
        case arch::memory::elf_section_type::DYNAMIC_SYMBOL_TABLE:
        case arch::memory::elf_section_type::SYMBOL_TABLE:
          symbol_table_section_count++;
          break;
        case arch::memory::elf_section_type::DYNAMIC:
          dynamic_section_count++;
          break;
        default:
          // All other cases are not important and can be ignored
          break;
      }
    }

    assert(symbol_table_section_count == 1U);
    assert(dynamic_section_count <= 1U);
  }

  auto main() -> void
  {
    using namespace video::vga;

    text::clear();
    text::cursor(false);
    text::write("TeachOS is starting up...", text::common_attributes::green_on_black);

    auto * multiboot_information_pointer =
        reinterpret_cast<arch::memory::multi_boot_info *>(arch::boot::multiboot_information_pointer);
    auto multiboot_tag = &(multiboot_information_pointer->tags);

    uint64_t kernel_start = UINT64_MAX;
    uint64_t kernel_end = 0;
    uint64_t multiboot_start = arch::boot::multiboot_information_pointer;
    uint64_t multiboot_end = multiboot_start + multiboot_information_pointer->total_size;
    arch::memory::memory_area * memory_areas = nullptr;
    uint8_t area_count = 0;

    /*
     * Loop over the multiboot2 tags to access the information needed.
     * Tags are defined in the header file and are padded so that each
     * Tag starts at an 8-bytes aligned adress.
     *
     * The increment part aligns the size to an 8-byte address.
     */
    for (auto tag = multiboot_tag; tag->type != arch::memory::multi_boot_tag_type::END;
         tag = reinterpret_cast<arch::memory::multi_boot_tag *>((reinterpret_cast<uint8_t *>(tag)) +
                                                                ((tag->size + 7) & ~7)))
    {
      switch (tag->type)
      {
        case arch::memory::multi_boot_tag_type::ELF_SECTIONS: {
          auto symbol = reinterpret_cast<teachos::arch::memory::elf_symbols_section *>(tag);
          process_elf_sections(symbol, kernel_start, kernel_end);
          break;
        }
        case arch::memory::multi_boot_tag_type::MEMORY_MAP: {
          auto mminfo = reinterpret_cast<teachos::arch::memory::memory_map *>(tag);
          process_memory_map(mminfo, memory_areas, area_count);
          break;
        }
        default:
          // All other cases are not important and can be ignored
          break;
      }
    }

    // Kernel start       0x100000
    // Kernel end         0x23E943
    //    Kernel Size       0x13E943 -> 1'304'899
    // Multiboot start    0x241AA0
    // Multiboot end      0x242280
    //    Multiboot Size    0x7E0 -> 2'016
    // Memory area start  0x241b10
    //
    // Address of Frame:  0x203F00
    auto allocator = arch::memory::area_frame_allocator(kernel_start, kernel_end, multiboot_start, multiboot_end,
                                                        memory_areas, area_count);
    auto allocated = allocator.allocate_frame();

    // WATCH OUT: using optional::value() crashes the build... I think its because of missing exception handling
    if (allocated.has_value())
    {
      video::vga::text::write("Allocated Frame address: ", video::vga::text::common_attributes::green_on_black);
      video::vga::text::write_number(reinterpret_cast<uint64_t>(&allocated->frame_number),
                                     video::vga::text::common_attributes::green_on_black);
      video::vga::text::write("Allocated Frame number: ", video::vga::text::common_attributes::green_on_black);
      video::vga::text::write_number(allocated->frame_number, video::vga::text::common_attributes::green_on_black);
    }
    else
    {
      video::vga::text::write("NO VALUE", video::vga::text::common_attributes::green_on_black);
    }
  }
}  // namespace teachos::arch::kernel