#include "kernel/filesystem/ext2/filesystem.hpp"

#include "kapi/devices/device.hpp"

#include "kernel/devices/block_device_utils.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>

namespace kernel::filesystem::ext2
{
  namespace
  {
    constexpr size_t SUPERBLOCK_OFFSET = 1024;
    constexpr uint16_t MAGIC_NUMBER = 0xEF53;

    constexpr uint32_t ROOT_INODE_NUMBER = 2;

    constexpr size_t DIRECT_BLOCK_COUNT = 12;
    constexpr size_t SINGLY_INDIRECT_BLOCK_INDEX = DIRECT_BLOCK_COUNT;
    constexpr size_t DOUBLY_INDIRECT_BLOCK_INDEX = SINGLY_INDIRECT_BLOCK_INDEX + 1;
    constexpr size_t TRIPLY_INDIRECT_BLOCK_INDEX = DOUBLY_INDIRECT_BLOCK_INDEX + 1;

    // Mode bits
    constexpr uint16_t S_IFMT = 0xF000;
    constexpr uint16_t S_IFREG = 0x8000;
    constexpr uint16_t S_IFDIR = 0x4000;

    auto S_ISREG(uint16_t mode) -> bool
    {
      return (mode & S_IFMT) == S_IFREG;
    }

    auto S_ISDIR(uint16_t mode) -> bool
    {
      return (mode & S_IFMT) == S_IFDIR;
    }
  }  // namespace

  auto filesystem::mount(kstd::shared_ptr<kapi::devices::device> const & device) -> int
  {
    kernel::filesystem::filesystem::mount(device);

    kernel::devices::block_device_utils::read(m_device, &m_superblock, SUPERBLOCK_OFFSET, sizeof(m_superblock));

    if (m_superblock.magic != MAGIC_NUMBER)
    {
      return -1;
    }

    auto const block_size = get_block_size();
    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);

    auto const block_group_descriptor_table_offset = block_size == 1024 ? 2 * block_size : block_size;
    kernel::devices::block_device_utils::read(m_device, m_block_group_descriptors.data(),
                                              block_group_descriptor_table_offset,
                                              num_block_groups * sizeof(block_group_descriptor));

    m_root_inode = read_inode(ROOT_INODE_NUMBER);
    // TODO BA-FS26 check if root inode is valid and is a directory ??
    return 0;
  }

  auto filesystem::lookup(kstd::shared_ptr<kernel::filesystem::inode> const & parent, std::string_view name)
      -> 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 block_size = get_block_size();
    auto const & inode_data = ext2_parent->m_data;
    kstd::vector<uint8_t> buffer(block_size);

    for (uint32_t i = 0; i < get_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;
      kernel::devices::block_device_utils::read(m_device, 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(uint32_t inode_number) -> kstd::shared_ptr<inode>
  {
    auto const block_size = get_block_size();
    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 * get_inode_size();

    auto new_inode = kstd::make_shared<inode>(this);
    kernel::devices::block_device_utils::read(m_device, &new_inode->m_data, inode_offset, sizeof(inode_data));

    // TODO BA-FS26 improve inode_kind really needed? or just map it to the mode bits?
    if (S_ISREG(new_inode->m_data.mode))
    {
      new_inode->m_kind = inode::inode_kind::regular;
    }
    else if (S_ISDIR(new_inode->m_data.mode))
    {
      new_inode->m_kind = inode::inode_kind::directory;
    }
    else
    {
      // TODO BA-FS26 really correct??
      return nullptr;
    }

    return new_inode;
  }

  auto filesystem::map_inode_block_index_to_global_block_number(uint32_t inode_block_index, inode_data data) -> uint32_t
  {
    if (inode_block_index < DIRECT_BLOCK_COUNT)
    {
      return data.block.at(inode_block_index);
    }
    inode_block_index -= DIRECT_BLOCK_COUNT;

    auto const block_size = get_block_size();
    auto const numbers_per_block = block_size / sizeof(uint32_t);

    auto const block_numbers_per_singly_indirect_block = numbers_per_block;
    auto const block_numbers_per_doubly_indirect_block = numbers_per_block * block_numbers_per_singly_indirect_block;
    auto const block_numbers_per_triply_indirect_block = numbers_per_block * block_numbers_per_doubly_indirect_block;

    if (inode_block_index < block_numbers_per_singly_indirect_block)
    {
      auto const singly_indirect_block_number = data.block.at(SINGLY_INDIRECT_BLOCK_INDEX);
      return read_block_number_at_index(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(DOUBLY_INDIRECT_BLOCK_INDEX);
      auto const singly_indirect_block_index_in_doubly_indirect_block =
          inode_block_index / 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);

      auto const block_index_in_singly_indirect_block = inode_block_index % block_numbers_per_singly_indirect_block;
      return read_block_number_at_index(singly_indirect_block_number, block_index_in_singly_indirect_block);
    }
    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(TRIPLY_INDIRECT_BLOCK_INDEX);
      auto const doubly_indirect_block_index_in_triply_indirect_block =
          inode_block_index / 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);

      auto const remaining_block_numbers = inode_block_index % block_numbers_per_doubly_indirect_block;

      auto const singly_indirect_block_index_in_doubly_indirect_block =
          remaining_block_numbers / 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);

      auto const block_index_in_singly_indirect_block =
          remaining_block_numbers % block_numbers_per_singly_indirect_block;
      return read_block_number_at_index(singly_indirect_block_number, block_index_in_singly_indirect_block);
    }

    return 0;  // TODO BA-FS26 really correct??
  }

  auto filesystem::read_block_number_at_index(uint32_t block_number, uint32_t index) -> uint32_t
  {
    uint32_t block_number_buffer = 0;

    auto const block_start_offset = block_number * get_block_size();
    auto const number_start_address = block_start_offset + index * sizeof(uint32_t);
    kernel::devices::block_device_utils::read(m_device, &block_number_buffer, number_start_address, sizeof(uint32_t));

    return block_number_buffer;
  }

  auto filesystem::get_block_size() -> size_t
  {
    return 1024U << m_superblock.log_block_size;
  }

  auto filesystem::get_inode_size() -> size_t
  {
    return m_superblock.rev_level == 0 ? 128 : m_superblock.inode_size;
  }

  auto filesystem::get_inode_block_count(inode_data const & data) -> uint32_t
  {
    return data.blocks / (2 << m_superblock.log_block_size);
  }
}  // namespace kernel::filesystem::ext2