#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/string>
#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;

    // 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 (size_t i = 0; i < DIRECT_BLOCK_COUNT && inode_data.block[i] != 0; ++i)
    {
      kernel::devices::block_device_utils::read(m_device, buffer.data(), inode_data.block[i] * block_size, block_size);

      size_t offset = 0;
      while (offset < block_size)
      {
        auto * entry = reinterpret_cast<linked_directory_entry const *>(buffer.data() + offset);
        if (entry->inode == 0)
          break;

        // Stop if the directory entry is malformed to avoid overruns/loops.
        // if (entry->rec_len < sizeof(linked_directory_entry) || offset + entry->rec_len > block_size)
        // {
        //   break;
        // }

        std::string_view entry_name(reinterpret_cast<char const *>(entry->name.data()), entry->name_len);
        if (entry_name == name)
        {
          return read_inode(entry->inode);
        }

        offset += entry->rec_len;
      }
    }

    return nullptr;
    // TODO BA-FS26 implement ext2 directory traversal and inode loading
    if (name == "dev")
    {
      // TODO BA-FS26 just for testing
      return nullptr;
    }

    return kstd::make_shared<inode>();
  }

  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>();
    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::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;
  }
}  // namespace kernel::filesystem::ext2