#include "kernel/filesystem/vfs.hpp"

#include "kapi/system.hpp"

#include "kernel/devices/device.hpp"
#include "kernel/devices/storage/storage_management.hpp"
#include "kernel/filesystem/custody.hpp"
#include "kernel/filesystem/device_file.hpp"
#include "kernel/filesystem/ext2/ext2_filesystem.hpp"
#include "kernel/filesystem/inode.hpp"
#include "kernel/filesystem/inode_file.hpp"
#include "kernel/filesystem/mount.hpp"
#include "kernel/filesystem/open_file_description.hpp"

#include <kstd/memory>

#include <algorithm>
#include <optional>
#include <string_view>

namespace filesystem
{
  namespace
  {
    constinit auto static active_vfs = std::optional<vfs>{};
  }  // namespace

  auto vfs::init() -> void
  {
    if (active_vfs)
    {
      kapi::system::panic("[FILESYSTEM] vfs has already been initialized.");
    }

    active_vfs.emplace(vfs{});

    auto storage_mgmt = devices::storage::storage_management::get();
    if (auto boot_device = storage_mgmt.determine_boot_device())
    {
      active_vfs->m_root_fs = kstd::make_shared<ext2::ext2_filesystem>();
      if (active_vfs->m_root_fs->mount(boot_device) != 0)
      {
        kapi::system::panic("[FILESYSTEM] Failed to mount root filesystem.");
      }

      active_vfs->m_root_mount = mount{"/", active_vfs->m_root_fs};

      std::ranges::for_each(storage_mgmt.all_controllers(), [&](auto controller) {
        std::ranges::for_each(controller->all_devices(), [&](auto device) { active_vfs->make_device_node(device); });
      });
    }
    else
    {
      // TODO BA-FS26 ?? what when no boot_device == no modules loaded??
    }
  }

  auto vfs::get() -> vfs &
  {
    if (!active_vfs)
    {
      kapi::system::panic("[FILESYSTEM] vfs has not been initialized.");
    }

    return *active_vfs;
  }

  auto vfs::open(std::string_view path) -> std::optional<open_file_description>
  {
    if (auto custody = resolve_path(path))
    {
      auto node = custody->get_inode();
      if (node->is_device())
      {
        auto current_device_file = kstd::make_shared<device_file>(node->backing_device());
        current_device_file->open();
        return open_file_description{current_device_file};
      }

      auto current_inode_file = kstd::make_shared<inode_file>(node);
      current_inode_file->open();
      return open_file_description{current_inode_file};
    }

    return std::nullopt;
  }

  auto vfs::make_device_node(kstd::shared_ptr<devices::device> const & device) -> void
  {
    if (!device)
    {
      kapi::system::panic("[FILESYSTEM] make_device_node called with null device.");
    }

    m_device_nodes.push_back(device_node_entry{device->name(), kstd::make_shared<inode>(device)});
  }

  auto vfs::resolve_path(std::string_view path) -> std::optional<custody>
  {
    // TODO BA-FS26 implement real path resolution with mounts and directories etc.
    // For now, just support device nodes at /dev/<device_name>.

    constexpr auto device_prefix = std::string_view{"/dev/"};
    if (path.starts_with(device_prefix))
    {
      auto const device_name = path.substr(device_prefix.size());
      auto entry = std::ranges::find_if(m_device_nodes, [&](auto const & device_entry) {
        return device_entry.has_value() && device_entry->name == device_name;
      });

      if (entry != m_device_nodes.end())
      {
        return custody{nullptr, entry->value().node};
      }

      return std::nullopt;
    }

    return std::nullopt;
  }

}  // namespace filesystem