#include "kernel/filesystem/vfs.hpp"

#include "kapi/system.hpp"

#include "kernel/devices/device.hpp"
#include "kernel/devices/storage/storage_management.hpp"
#include "kernel/filesystem/dentry.hpp"
#include "kernel/filesystem/device_inode.hpp"
#include "kernel/filesystem/ext2/ext2_filesystem.hpp"
#include "kernel/filesystem/filesystem.hpp"
#include "kernel/filesystem/mount.hpp"
#include "kernel/filesystem/open_file_description.hpp"

#include <kstd/memory>

#include <algorithm>
#include <optional>
#include <ranges>
#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{});
    active_vfs->init_internal();
  }

  auto vfs::init_internal() -> void
  {
    auto storage_mgmt = devices::storage::storage_management::get();
    if (auto boot_device = storage_mgmt.determine_boot_device())
    {
      auto root_fs = kstd::make_shared<ext2::ext2_filesystem>();
      root_fs->mount(boot_device);

      auto root_dentry = kstd::make_shared<dentry>(nullptr, root_fs->root_inode(), "/");
      root_fs->set_root_dentry(root_dentry);

      m_mount_table.add_mount(kstd::make_shared<mount>(nullptr, root_fs));

      // TODO BA-FS26 use do_mount when tempdevfs is implemented -> just call /dev/ with all devices in devtempfs
      std::ranges::for_each(storage_mgmt.all_controllers(), [&](auto controller) {
        std::ranges::for_each(controller->all_devices(), [&](auto device) { 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) -> kstd::shared_ptr<open_file_description>
  {
    if (auto dentry = resolve_path(path))
    {
      return kstd::make_shared<open_file_description>(dentry->get_inode());
    }

    return nullptr;
  }

  auto vfs::do_mount(std::string_view path, kstd::shared_ptr<filesystem> const & filesystem) -> int
  {
    if (!filesystem)
    {
      return -1;  // TODO BA-FS26 panic or errorcode?
    }

    if (path.empty() || path.front() != '/')
    {
      return -1;  // TODO BA-FS26 panic or errorcode?
    }

    // TODO BA-FS26 better path validation
    if ((path.size() > 1 && path.back() == '/'))
    {
      return -1;  // TODO BA-FS26 panic or errorcode?
    }

    if (auto mount_dentry = resolve_path(path))
    {
      // TODO BA-FS26 check if mount point is already mounted and handle it (unmount old fs, fail, etc.)

      mount_dentry->set_flag(dentry::dentry_flags::dcache_mounted);
      m_mount_table.add_mount(kstd::make_shared<mount>(mount_dentry, filesystem));

      filesystem->set_root_dentry(kstd::make_shared<dentry>(mount_dentry->get_parent(), filesystem->root_inode()));

      return 0;
    }

    return -1;
  }

  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().view(), kstd::make_shared<device_inode>(device)});
  }

  auto vfs::resolve_path(std::string_view path) -> kstd::shared_ptr<dentry>
  {
    // TODO BA-FS26 implement real path resolution with mounts and directories etc.
    // For now, just support device nodes at /dev/<device_name>.
    // TODO BA-FS26 better path validation
    // TODO BA-FS26 implement a path parser (maybe in libs?) and use it here and in do_mount

    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 kstd::make_shared<dentry>(nullptr, entry->value().node);
      }

      return nullptr;
    }
    else if (!path.empty() && path.front() == '/')
    {
      auto root_mount = m_mount_table.get_root_mount();
      if (!root_mount)
      {
        kapi::system::panic("[FILESYSTEM] no root mount found.");
      }

      auto current_dentry = root_mount->get_dentry();
      auto current_fs = root_mount->get_filesystem();

      auto path_parts =
          std::views::split(path, '/') | std::views::filter([](auto const & part) { return !part.empty(); });
      for (auto const & part : path_parts)
      {
        auto next_dentry = current_dentry->find_child(std::string_view{part});

        if (!next_dentry)
        {
          if (auto found_inode = current_fs->lookup(current_dentry->get_inode(), std::string_view{part}))
          {
            next_dentry = kstd::make_shared<dentry>(current_dentry, found_inode, std::string_view{part});
            current_dentry->add_child(next_dentry);
          }
          else
          {
            return nullptr;
          }
        }

        if (next_dentry->has_flag(dentry::dentry_flags::dcache_mounted))
        {
          auto found_mount = m_mount_table.find_mount_by_dentry(next_dentry);
          current_fs = found_mount->get_filesystem();
          current_dentry = current_fs->root_dentry();
        }
        else
        {
          current_dentry = next_dentry;
        }
      }

      return current_dentry;
    }

    return nullptr;
  }

}  // namespace filesystem