defmodule LayoutOMatic.Button do
  # Buttons size based on :button_font_size with 20 being the default; width/height override. Button position is based on the top left point.
  @default_font_size 20
  @default_font :roboto

  @spec translate(%{
          component: map,
          starting_xy: {number, number},
          grid_xy: {number, number},
          max_xy: {number, number}
        }) ::
          {:error, <<_::160, _::_*32>>}
          | {:ok, {number, number},
             %{
               grid_xy: {number, number},
               max_xy: number,
               primitive: %{data: number, styles: map},
               starting_xy: {number, number}
             }}

  def translate(
        %{
          component: component,
          starting_xy: starting_xy,
          grid_xy: grid_xy,
          max_xy: max_xy
        } = layout
      ) do
    {_, text} = Map.get(component, :data)

    styles = button_size(component)

    %{font_size: font_size, ascent: ascent, fm_width: fm_width} =
      get_font_metrics(text, Map.get(styles, :button_font_size))

    height =
      case Map.get(styles, :height) do
        nil -> font_size + ascent
        :auto -> font_size + ascent
        height when is_number(height) and height > 0 -> height
      end

    width =
      case Map.get(styles, :width) do
        nil -> fm_width + ascent + ascent
        :auto -> fm_width + ascent + ascent
        width when is_number(width) and width > 0 -> width
      end

    {starting_x, starting_y} = starting_xy
    {grid_x, grid_y} = grid_xy

    if starting_xy == grid_xy do
      layout = Map.put(layout, :starting_xy, {starting_x + width, starting_y})
      # already in a new group, use starting_xy
      {:ok, {starting_x, starting_y}, layout}
    else
      if fits_in_x?(starting_x + width, max_xy) do
        # fits in x
        # fit in y?
        if fits_in_y?(starting_y + height, max_xy) do
          # fits
          layout = Map.put(layout, :starting_xy, {starting_x + width, starting_y})
          {:ok, {starting_x, starting_y}, layout}

          # Does not fit
        else
          {:error, "Does not fit in grid"}
        end
      else
        # fit in new y?
        # doesnt fit in x
        new_y = grid_y + height

        if fits_in_y?(new_y, max_xy) do
          # fits in new y, check x
          new_layout =
            layout
            |> Map.put(:grid_xy, {grid_x, new_y})
            |> Map.put(:starting_xy, {width, new_y})

          {:ok, {grid_x, new_y}, new_layout}
        else
          {:error, "Does not fit in the grid"}
        end
      end
    end
  end

  defp button_size(%{styles: %{width: _, height: _, button_font_size: _}} = styles), do: styles

  defp button_size(%{styles: %{width: _, height: _}} = styles),
    do: Map.put(styles, :button_font_size, @default_font_size)

  defp button_size(_), do: Map.new(button_font_size: @default_font_size)

  defp get_font_metrics(text, font_size) do
    fm = Scenic.Cache.Static.FontMetrics.get!(@default_font)
    ascent = FontMetrics.ascent(font_size, fm)
    fm_width = FontMetrics.width(text, font_size, fm)

    %{font_size: font_size, ascent: ascent, fm_width: fm_width}
  end

  defp fits_in_x?(potential_x, {max_x, _}),
    do: potential_x <= max_x

  defp fits_in_y?(potential_y, {_, max_y}),
    do: potential_y <= max_y
end