raxol_terminal

defmodule Raxol.Terminal.Modes.Handlers.ScreenBufferHandler do
  @moduledoc """
  Handles screen buffer mode operations and their side effects.
  Manages alternate screen buffer switching and related functionality.
  """


  alias Raxol.Terminal.ANSI.TextFormatting
  alias Raxol.Terminal.Emulator
  alias Raxol.Terminal.ModeManager
  alias Raxol.Terminal.Modes.Types.ModeTypes

  @screen_buffer_module Application.compile_env(
                          :raxol,
                          :screen_buffer_impl,
                          Raxol.Terminal.ScreenBuffer
                        )

  @doc """
  Handles a screen buffer mode change and applies its effects to the emulator.
  """
  @spec handle_mode_change(atom(), ModeTypes.mode_value(), Emulator.t()) ::
          {:ok, Emulator.t()} | {:error, term()}
  def handle_mode_change(mode_name, value, emulator) do
    case find_mode_definition(mode_name) do
      %{category: :screen_buffer} = mode_def ->
        apply_mode_effects(mode_def, value, emulator)

      _ ->
        {:error, :invalid_mode}
    end
  end

  # Private Functions

  defp find_mode_definition(mode_name) do
    ModeTypes.get_all_modes()
    |> Map.values()
    |> Enum.find(&(&1.name == mode_name))
  end

  defp apply_mode_effects(mode_def, value, emulator) do
    case mode_def.name do
      :dec_alt_screen ->
        handle_simple_alt_screen(value, emulator)

      :dec_alt_screen_save ->
        handle_alt_screen_with_save(value, emulator)

      :alt_screen_buffer ->
        handle_alt_screen_with_clear(value, emulator)

      :decsc_deccara ->
        handle_cursor_save_restore(value, emulator)

      _ ->
        {:error, :unsupported_mode}
    end
  end

  defp handle_simple_alt_screen(true, emulator) do
    # Mode 47: Simple alternate screen buffer
    with {:ok, alt_buffer} <- create_or_get_alt_buffer(emulator) do
      {:ok,
       %{
         emulator
         | alternate_screen_buffer: alt_buffer,
           active_buffer_type: :alternate
       }}
    end
  end

  defp handle_simple_alt_screen(false, emulator) do
    # Switch back to main buffer
    {:ok, %{emulator | active_buffer_type: :main}}
  end

  defp handle_alt_screen_with_save(true, emulator) do
    # Mode 1047: Alt screen with save/restore
    with {:ok, alt_buffer} <- create_or_get_alt_buffer(emulator),
         {:ok, emulator_with_saved_state} <- save_terminal_state(emulator) do
      # Set alternate_buffer_active to true in mode_manager
      new_mode_manager =
        Map.put(
          emulator_with_saved_state.mode_manager,
          :alternate_buffer_active,
          true
        )

      # Reset cursor position to (0, 0) when switching to alternate buffer
      updated_cursor =
        Raxol.Terminal.Cursor.Manager.set_position(
          emulator_with_saved_state.cursor,
          {0, 0}
        )

      {:ok,
       %{
         emulator_with_saved_state
         | alternate_screen_buffer: alt_buffer,
           active_buffer_type: :alternate,
           mode_manager: new_mode_manager,
           cursor: updated_cursor
       }}
    end
  end

  defp handle_alt_screen_with_save(false, emulator) do
    # Switch back to main buffer and restore state
    with {:ok, emulator_with_restored_state} <- restore_terminal_state(emulator) do
      # Set alternate_buffer_active to false in mode_manager
      new_mode_manager =
        Map.put(
          emulator_with_restored_state.mode_manager,
          :alternate_buffer_active,
          false
        )

      {:ok,
       %{
         emulator_with_restored_state
         | active_buffer_type: :main,
           mode_manager: new_mode_manager
       }}
    end
  end

  defp handle_alt_screen_with_clear(true, emulator) do
    # Mode 1049: Alt screen with save/restore and clear
    with {:ok, alt_buffer} <- create_or_get_alt_buffer(emulator),
         {:ok, emulator_with_saved_state} <- save_terminal_state(emulator) do
      # Clear the alternate buffer
      cleared_alt_buffer =
        @screen_buffer_module.clear(
          alt_buffer,
          TextFormatting.new()
        )

      # Create a fresh mode manager with default values for alternate screen
      # but preserve certain critical modes that should persist
      default_mode_manager = ModeManager.new()

      updated_mode_manager = %{
        default_mode_manager
        | alternate_buffer_active: true,
          # Preserve only critical modes that should persist across screen switches
          interlacing_mode: emulator_with_saved_state.mode_manager.interlacing_mode
      }

      {:ok,
       %{
         emulator_with_saved_state
         | alternate_screen_buffer: cleared_alt_buffer,
           active_buffer_type: :alternate,
           mode_manager: updated_mode_manager
       }}
    end
  end

  defp handle_alt_screen_with_clear(false, emulator) do
    # Switch back to main buffer, restore state, and clear alt buffer
    with {:ok, emulator_with_restored_state} <- restore_terminal_state(emulator) do
      # Clear the alternate buffer before switching away
      case emulator_with_restored_state.alternate_screen_buffer do
        nil ->
          {:ok, %{emulator_with_restored_state | active_buffer_type: :main}}

        alt_buf ->
          cleared_alt_buf =
            @screen_buffer_module.clear(
              alt_buf,
              TextFormatting.new()
            )

          {:ok,
           %{
             emulator_with_restored_state
             | alternate_screen_buffer: cleared_alt_buf,
               active_buffer_type: :main
           }}
      end
    end
  end

  defp create_or_get_alt_buffer(emulator) do
    case emulator.alternate_screen_buffer do
      nil ->
        {width, height} =
          @screen_buffer_module.get_dimensions(emulator.main_screen_buffer)

        {:ok, @screen_buffer_module.new(width, height)}

      alt_buffer ->
        {:ok, alt_buffer}
    end
  end

  defp save_terminal_state(emulator) do
    # Get the terminal state implementation
    terminal_state_module =
      Application.get_env(
        :raxol,
        :terminal_state_impl,
        Raxol.Terminal.ANSI.TerminalState
      )

    # Save the current state
    new_stack = terminal_state_module.save_state(emulator.state_stack, emulator)
    {:ok, %{emulator | state_stack: new_stack}}
  end

  defp restore_terminal_state(emulator) do
    # Get the terminal state implementation
    terminal_state_module =
      Application.get_env(
        :raxol,
        :terminal_state_impl,
        Raxol.Terminal.ANSI.TerminalState
      )

    # Restore the previous state
    {restored_state, new_stack} =
      terminal_state_module.restore_state(emulator.state_stack)

    case restored_state do
      nil ->
        {:ok, emulator}

      state ->
        # Apply the restored state
        emulator_with_restored_state =
          terminal_state_module.apply_restored_data(
            emulator,
            state,
            [
              :cursor,
              :style,
              :charset_state,
              :mode_manager,
              :scroll_region,
              :cursor_style
            ]
          )

        {:ok, %{emulator_with_restored_state | state_stack: new_stack}}
    end
  end

  defp handle_cursor_save_restore(true, emulator) do
    # Mode 1048: Save cursor position and attributes
    save_terminal_state(emulator)
  end

  defp handle_cursor_save_restore(false, emulator) do
    # Mode 1048: Restore cursor position and attributes only
    restore_cursor_only(emulator)
  end

  defp restore_cursor_only(emulator) do
    # Get the terminal state implementation
    terminal_state_module =
      Application.get_env(
        :raxol,
        :terminal_state_impl,
        Raxol.Terminal.ANSI.TerminalState
      )

    # Restore the previous state
    {restored_state, new_stack} =
      terminal_state_module.restore_state(emulator.state_stack)

    # Only restore the cursor position
    emulator =
      terminal_state_module.apply_restored_data(emulator, restored_state, [
        :cursor
      ])

    {:ok, %{emulator | state_stack: new_stack}}
  end
end