A console-based startmenu for Rubyinstaller

startmenu.rb

require "io/console"

class ButtonMatrix

  attr_accessor :selected

  def initialize(ncols: 3)
    @ncols = ncols
    @boxes = []
    @con = IO.console
    @selected = 0
  end

  Box = Data.define :text, :action
  def add_button(text, &action)
    @boxes << Box.new(text, action)
  end

  def cursor(direction)
    case direction
    when :left
      @selected -= 1 if @selected > 0
    when :up
      @selected -= @ncols if @selected - @ncols >= 0
    when :right
      @selected += 1 if @selected + 1 < @boxes.size
    when :down
      @selected += @ncols if @selected + @ncols < @boxes.size
    end
  end

  def select
    @boxes[@selected].action.call
  end

  BUTTON_BORDERS = {
    thin:   "┌─┐" +
            "│ │" +
            "└─┘" ,
    fat:    "┏━┓" +
            "┃ ┃" +
            "┗━┛" ,
    double: "╔═╗" +
            "║ ║" +
            "╚═╝" ,
  }

  private def box_border(ncol, nrow)
    box_idx = ncol + nrow * @ncols
    selected = box_idx == @selected
    border = BUTTON_BORDERS[selected ? :double : :thin]
    box = @boxes[box_idx]&.text
    return box, border
  end

  # Paint the boxes
  def repaint(width: @con.winsize[1], height: @con.winsize[0] - 1)
    obw = (width.to_f / @ncols).floor
    spw = obw - 4
    nrows = (@boxes.size.to_f / @ncols).ceil
    obh = (height.to_f / nrows).floor
    sph = obh - 2
    line = +""
    nrows.times do |nrow|
      @ncols.times do |ncol|
        box, border = box_border(ncol, nrow)
        if box
          line += " #{border[0]}" + "#{border[1]}" * spw + "#{border[2]} "
        end
      end
      line += "\n"
      sph.times do |spy|
        @ncols.times do |ncol|
          box, border = box_border(ncol, nrow)
          if box
            text_lines = box.lines.map(&:chomp)
            text_pos = spy - (sph - text_lines.size) / 2
            text_line = text_lines[text_pos] if text_pos >= 0
            text_line ||= ""
            spl = (spw - text_line.size) / 2
            spr = spw - spl - text_line.size
            line += " #{border[3]}" + " " * spl + text_line + " " * spr + "#{border[5]} "
          end
        end
        line += "\n"
      end
      @ncols.times do |ncol|
        box, border = box_border(ncol, nrow)
        if box
          line += " #{border[6]}" + "#{border[7]}" * spw + "#{border[8]} "
        end
      end
      line += "\n"
    end
    print line
  end
end

class ConsoleApp
  attr_accessor :widget

  def initialize
    @ev_r, @ev_w = IO.pipe

    register_term_size_change
    register_stdin
  end

  private def register_term_size_change
    if RUBY_PLATFORM =~ /mingw|mswin/
      IO.console.check_winsize_changed do
        @ev_w.write "\x01"
      end
    else
      Signal.trap('SIGWINCH') do
        @ev_w.write "\x01"
      end
    end
  end

  private def register_stdin
    Thread.new do
      str = +""
      while char=$stdin.getch(intr: true)
        str << char
        next if !str.valid_encoding? || str == "\e" || str == "\e["

        @ev_w.write [2, str.size, str].pack("CCa*")
        str = +""
      end
    end
  end

  private def handle_key_input(str)
    case str
    when "\e[D" # cursor left
      widget.cursor(:left)
    when "\e[A" # cursor up
      widget.cursor(:up)
    when "\e[C" # cursor right
      widget.cursor(:right)
    when "\e[B" # cursor down
      widget.cursor(:down)
    when "\r" # enter
      widget.select
    end
    widget.repaint
  end

  private def main_loop
    str = +""
    while char=@ev_r.getc
      case char
      when "\x01"
        widget.repaint
      when "\x02"
        strlen = @ev_r.getc.unpack1("C")
        str = @ev_r.read(strlen)

        handle_key_input(str)
        widget.repaint
      else
        raise "unexpected event: #{char.inspect}"
      end
    end
  end

  def run!
    widget.repaint
    main_loop
  end
end

app = ConsoleApp.new
bm = ButtonMatrix.new ncols: 3
bm.add_button "text1\nabc" do
  p :button_1
  exit
end
bm.add_button "text2" do
  p :button_2
end
bm.add_button "text3\nabc\noollla\n text3\nabc\noollla" do
  p :button_3
end
bm.add_button "text4\ndef" do
  p :button_4
end
bm.add_button "text5\nabc" do
  p :button_5
end
app.widget = bm
app.run!