defmodule AccurateMinimalRepro do
  defmodule Cursor do
    defstruct [:current, :position]
    
    def from_list(list, opts \\ []) do
      position = Keyword.get(opts, :position, 0)
      %__MODULE__{current: Enum.at(list, position), position: position}
    end
    
    def to_list(%__MODULE__{}), do: []
    
    def move_forward(%__MODULE__{} = cursor), do: cursor
    
    def delete_before(%__MODULE__{} = cursor, _count), do: cursor
    
    def insert_before(%__MODULE__{} = cursor, _items), do: cursor
  end

  def test_function do
    diffs = Cursor.from_list([{:equal, "test"}])
    line_mode_loop(diffs, {0, 0, "", ""}, :never)
  end

  defp line_mode_loop(
          %Cursor{current: nil} = diffs,
          _acc,
          _deadline
        ),
        do: Cursor.to_list(diffs)

  defp line_mode_loop(
          %Cursor{current: this_diff} = diffs,
          {count_delete, count_insert, text_delete, text_insert},
          deadline
        ) do
    {op, text} = this_diff

    result =
      case op do
        :insert ->
          {diffs, count_delete, count_insert + 1, text_delete, text_insert <> text}

        :delete ->
          {diffs, count_delete + 1, count_insert, text_delete <> text, text_insert}

        :equal ->
          diffs2 =
            if count_delete > 0 && count_insert > 0 do
              temp_diffs = Cursor.delete_before(diffs, count_delete + count_insert)
              sub_diff = main_impl(text_delete, text_insert, false, deadline)
              Cursor.insert_before(temp_diffs, sub_diff)
            else
              diffs
            end
          {diffs2, 0, 0, "", ""}

        _ ->
          raise RuntimeError, "Invalid operation"
      end

    {cursor, count_delete, count_insert, text_delete, text_insert} = result

    line_mode_loop(
      Cursor.move_forward(cursor),
      {count_delete, count_insert, text_delete, text_insert},
      deadline
    )
  end

  defp main_impl(_text1, _text2, _check_lines, _deadline) do
    [{:equal, "stub"}]
  end
end