#include <kernel/filesystem/ext2/filesystem.hpp>

#include <kernel/filesystem/ext2/block_group_descriptor.hpp>
#include <kernel/filesystem/ext2/inode.hpp>
#include <kernel/filesystem/ext2/linked_directory_entry.hpp>
#include <kernel/filesystem/ext2/superblock.hpp>
#include <kernel/filesystem/filesystem.hpp>
#include <kernel/filesystem/inode.hpp>

#include <kstd/memory>
#include <kstd/vector>

#include <cstddef>
#include <cstdint>
#include <string_view>
#include <unistd.h>

namespace kernel::filesystem::ext2
{
  auto filesystem::mount(kstd::shared_ptr<kernel::filesystem::inode> const & backing_inode) -> operation_result
  {
    kernel::filesystem::filesystem::mount(backing_inode);

    m_backing_inode->read(&m_superblock, constants::superblock_offset, sizeof(m_superblock));

    if (m_superblock.magic != constants::magic_number)
    {
      return operation_result::invalid_magic_number;
    }

    auto const blocks_per_group = m_superblock.blocks_per_group;
    auto const num_block_groups = (m_superblock.blocks_count + blocks_per_group - 1) / blocks_per_group;

    m_block_group_descriptors = kstd::vector<block_group_descriptor>(num_block_groups);

    m_backing_inode->read(m_block_group_descriptors.data(), block_group_descriptor_table_offset(),
                          num_block_groups * sizeof(block_group_descriptor));

    m_root_inode = read_inode(constants::root_inode_number);

    if (!m_root_inode || !m_root_inode->is_directory())
    {
      return operation_result::invalid_root_inode;
    }
    return operation_result::success;
  }

  auto filesystem::lookup(kstd::shared_ptr<kernel::filesystem::inode> const & parent, std::string_view name) const
      -> kstd::shared_ptr<kernel::filesystem::inode>
  {
    if (!parent || !parent->is_directory())
    {
      return nullptr;
    }

    auto * ext2_parent = static_cast<inode *>(parent.get());
    if (!ext2_parent)
    {
      return nullptr;
    }

    auto const & inode_data = ext2_parent->data();
    kstd::vector<uint8_t> buffer(block_size());

    for (auto i = 0uz; i < inode_block_count(inode_data); ++i)
    {
      auto const global_block_number = map_inode_block_index_to_global_block_number(i, inode_data);
      auto const block_offset = global_block_number * block_size();
      m_backing_inode->read(buffer.data(), block_offset, block_size());

      auto const * entry = reinterpret_cast<linked_directory_entry const *>(buffer.data());
      auto bytes_read = 0uz;

      while (bytes_read < block_size() && entry->inode != 0)
      {
        auto const entry_name = std::string_view{entry->name.data(), entry->name_len};
        if (entry_name == name)
        {
          return read_inode(entry->inode);
        }

        bytes_read += entry->rec_len;
        entry = reinterpret_cast<linked_directory_entry const *>(buffer.data() + bytes_read);
      }
    }

    return nullptr;
  }

  auto filesystem::read_inode(size_t inode_number) const -> kstd::shared_ptr<inode>
  {
    auto const inodes_per_group = m_superblock.inodes_per_group;
    auto const block_group_index = (inode_number - 1) / inodes_per_group;
    auto const inode_index_within_group = (inode_number - 1) % inodes_per_group;

    if (block_group_index >= m_block_group_descriptors.size())
    {
      return nullptr;
    }

    auto const & block_group_descriptor = m_block_group_descriptors.at(block_group_index);
    auto const inode_table_start_block = block_group_descriptor.inode_table;
    auto const inode_table_offset = static_cast<size_t>(inode_table_start_block) * block_size();
    auto const inode_offset = inode_table_offset + inode_index_within_group * inode_size();

    auto new_inode_data = inode_data{};
    m_backing_inode->read(&new_inode_data, inode_offset, sizeof(inode_data));

    return kstd::make_shared<inode>(this, new_inode_data);
  }

  auto filesystem::map_inode_block_index_to_global_block_number(size_t inode_block_index, inode_data data) const
      -> ssize_t
  {
    if (inode_block_index < constants::direct_block_count)
    {
      return data.block.at(inode_block_index);
    }
    inode_block_index -= constants::direct_block_count;

    if (inode_block_index < block_numbers_per_singly_indirect_block())
    {
      auto const singly_indirect_block_number = data.block.at(constants::singly_indirect_block_index);
      return read_singly_indirect_block_number(singly_indirect_block_number, inode_block_index);
    }
    inode_block_index -= block_numbers_per_singly_indirect_block();

    if (inode_block_index < block_numbers_per_doubly_indirect_block())
    {
      auto const doubly_indirect_block_number = data.block.at(constants::doubly_indirect_block_index);
      return read_doubly_indirect_block_number(doubly_indirect_block_number, inode_block_index);
    }
    inode_block_index -= block_numbers_per_doubly_indirect_block();

    if (inode_block_index < block_numbers_per_triply_indirect_block())
    {
      auto const triply_indirect_block_number = data.block.at(constants::triply_indirect_block_index);
      return read_triply_indirect_block_number(triply_indirect_block_number, inode_block_index);
    }

    return -1;
  }

  auto filesystem::read_singly_indirect_block_number(size_t singly_indirect_block_number,
                                                     size_t block_index_in_singly_indirect_block) const -> size_t
  {
    if (singly_indirect_block_number == 0)
    {
      return 0;
    }

    return read_block_number_at_index(singly_indirect_block_number, block_index_in_singly_indirect_block);
  }

  auto filesystem::read_doubly_indirect_block_number(size_t doubly_indirect_block_number,
                                                     size_t block_index_in_doubly_indirect_block) const -> size_t
  {
    if (doubly_indirect_block_number == 0)
    {
      return 0;
    }

    auto const singly_indirect_block_index_in_doubly_indirect_block =
        block_index_in_doubly_indirect_block / block_numbers_per_singly_indirect_block();
    auto const block_index_in_singly_indirect_block =
        block_index_in_doubly_indirect_block % block_numbers_per_singly_indirect_block();

    auto const singly_indirect_block_number =
        read_block_number_at_index(doubly_indirect_block_number, singly_indirect_block_index_in_doubly_indirect_block);

    return read_singly_indirect_block_number(singly_indirect_block_number, block_index_in_singly_indirect_block);
  }

  auto filesystem::read_triply_indirect_block_number(size_t triply_indirect_block_number,
                                                     size_t block_index_in_triply_indirect_block) const -> size_t
  {
    if (triply_indirect_block_number == 0)
    {
      return 0;
    }

    auto const doubly_indirect_block_index_in_triply_indirect_block =
        block_index_in_triply_indirect_block / block_numbers_per_doubly_indirect_block();
    auto const block_index_in_doubly_indirect_block =
        block_index_in_triply_indirect_block % block_numbers_per_doubly_indirect_block();

    auto const doubly_indirect_block_number =
        read_block_number_at_index(triply_indirect_block_number, doubly_indirect_block_index_in_triply_indirect_block);

    return read_doubly_indirect_block_number(doubly_indirect_block_number, block_index_in_doubly_indirect_block);
  }

  auto filesystem::read_block_number_at_index(size_t block_number, size_t index) const -> size_t
  {
    auto block_number_buffer = 0uz;

    auto const block_start_offset = block_number * block_size();
    auto const number_start_address = block_start_offset + index * sizeof(uint32_t);
    m_backing_inode->read(&block_number_buffer, number_start_address, sizeof(uint32_t));

    return block_number_buffer;
  }

  auto filesystem::block_numbers_per_block() const -> size_t
  {
    return block_size() / sizeof(uint32_t);
  }

  auto filesystem::block_numbers_per_singly_indirect_block() const -> size_t
  {
    return block_numbers_per_block();
  }

  auto filesystem::block_numbers_per_doubly_indirect_block() const -> size_t
  {
    return block_numbers_per_singly_indirect_block() * block_numbers_per_block();
  }

  auto filesystem::block_numbers_per_triply_indirect_block() const -> size_t
  {
    return block_numbers_per_doubly_indirect_block() * block_numbers_per_block();
  }

  auto filesystem::block_size() const -> size_t
  {
    return constants::base_block_size << m_superblock.log_block_size;
  }

  auto filesystem::revision_level() const -> size_t
  {
    return m_superblock.rev_level;
  }

  auto filesystem::inode_size() const -> size_t
  {
    return revision_level() == constants::good_old_revision ? 128 : m_superblock.inode_size;
  }

  auto filesystem::inode_block_count(inode_data const & data) const -> size_t
  {
    return data.blocks / (2 << m_superblock.log_block_size);
  }

  auto filesystem::block_group_descriptor_table_offset() const -> size_t
  {
    return block_size() == 1024 ? 2 * block_size() : block_size();
  }
}  // namespace kernel::filesystem::ext2