#include "filesystem/device_file.hpp"

#include "kapi/system.hpp"

#include "devices/block_device.hpp"
#include "devices/device.hpp"

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

#include <algorithm>
#include <cstddef>

namespace filesystem
{
  device_file::device_file(kstd::shared_ptr<devices::device> const & device)
      : m_device(device)
  {
    if (!m_device)
    {
      kapi::system::panic("[FILESYSTEM] device_file constructed with null device.");
    }
  }

  auto device_file::open() -> void
  {
    // Hook point for permission checks or lazy metadata loading.
  }

  auto device_file::read(void * buffer, size_t offset, size_t size) const -> size_t
  {
    if (m_device->is_block_device())
    {
      return process_blocks(offset, size, buffer,
                            [](size_t idx, size_t off, size_t len, size_t done, devices::block_device * device,
                               std::byte * scratch, void * buffer) {
                              auto * out = static_cast<std::byte *>(buffer);
                              if (off == 0 && len == device->block_size())
                              {
                                device->read_block(idx, out + done);
                              }
                              else
                              {
                                device->read_block(idx, scratch);
                                kstd::libc::memcpy(out + done, scratch + off, len);
                              }
                            });
    }
    else
    {
      kapi::system::panic("[FILESYSTEM] device_file::read called on non-block device.");
    }
  }

  auto device_file::write(void const * buffer, size_t offset, size_t size) -> size_t
  {
    if (m_device->is_block_device())
    {
      return process_blocks(offset, size, const_cast<void *>(buffer),
                            [](size_t idx, size_t off, size_t len, size_t done, devices::block_device * device,
                               std::byte * scratch, void * buffer) {
                              auto const * in = static_cast<std::byte const *>(buffer);
                              if (off == 0 && len == device->block_size())
                              {
                                device->write_block(idx, in + done);
                              }
                              else
                              {
                                device->read_block(idx, scratch);
                                kstd::libc::memcpy(scratch + off, in + done, len);
                                device->write_block(idx, scratch);
                              }
                            });
    }
    else
    {
      kapi::system::panic("[FILESYSTEM] device_file::write called on non-block device.");
    }
  }

  auto device_file::process_blocks(size_t offset, size_t size, void * buffer, block_op op) const -> size_t
  {
    if (buffer == nullptr)
    {
      kapi::system::panic("[FILESYSTEM] device_file::write called with null buffer.");
    }

    if (size == 0)
    {
      return 0;
    }

    // @Felix rtti not activated why? e.g. dynamic_cast does not work, whats with std::dynamic_pointer_cast
    // online: rtti overhead, bad design, ... ?
    auto * block_dev = static_cast<devices::block_device *>(m_device.get());
    if (block_dev == nullptr)
    {
      kapi::system::panic("[FILESYSTEM] device_file: expected block_device.");
    }

    size_t const block_size = block_dev->block_size();
    size_t const capacity = block_dev->capacity();

    if (offset >= capacity)
      return 0;
    size_t const total_to_process = std::min(size, capacity - offset);

    kstd::vector<std::byte> scratch_buffer{block_size};
    auto processed = 0uz;

    while (processed < total_to_process)
    {
      size_t const absolute_offset = offset + processed;
      size_t const block_index = absolute_offset / block_size;
      size_t const in_block_offset = absolute_offset % block_size;
      size_t const chunk_size = std::min(total_to_process - processed, block_size - in_block_offset);

      op(block_index, in_block_offset, chunk_size, processed, block_dev, scratch_buffer.data(), buffer);

      processed += chunk_size;
    }

    return processed;
  }
}  // namespace filesystem