#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_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 <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->do_mount("/", active_vfs->m_root_fs) != 0)
      {
        kapi::system::panic("[FILESYSTEM] Failed to mount root filesystem.");
      }

      // 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) { 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) -> kstd::shared_ptr<open_file_description>
  {
    if (auto custody = resolve_path(path))
    {
      auto node = custody->get_inode();

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

      kapi::system::panic("[FILESYSTEM] inode::open_file returned null file.");
    }

    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() == '/') || path.find("//") != std::string_view::npos)
    {
      return -1;  // TODO BA-FS26 panic or errorcode?
    }

    if (path == "/")
    {
      m_root_fs = filesystem;
      m_root_mount = mount{"/", filesystem};
      return 0;
    }

    auto existing_mount =
        std::ranges::find_if(m_mounts, [&](auto const & existing) { return existing.path() == path; });
    if (existing_mount != m_mounts.end())
    {
      *existing_mount = mount{path, filesystem};
    }
    else
    {
      m_mounts.push_back(mount{path, filesystem});
    }

    return 0;
  }

  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<device_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>.
    // 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 custody{nullptr, entry->value().node};
      }

      return std::nullopt;
    }

    return std::nullopt;
  }

}  // namespace filesystem