Text editor using reline

reline_editor.rb

require 'irb'
require 'reline'

$status = nil
Reline::Face.config(:editor_status) do |face|
  face.define :default, foreground: :white, background: :blue
end
Reline.add_dialog_proc :editor_status, ->(*) do
  if (message = $status)
    $status = nil
    pos = Reline::CursorPos.new(cursor_pos.x, -1)
    Reline::DialogRenderInfo.new(pos: pos, contents: message.lines, face: :editor_status)
  end
end

def edit(file)
  Reline.prompt_proc = ->(lines) do
    n = [(lines.size + 1).to_s.size, 3].max
    format = "%0#{n}d> "
    (1..lines.size).map { format % _1 }
  end
  Reline::LineEditor.define_method(:_editor_save) do |_key|
    begin
      File.write(file, whole_buffer)
      $status = "Saved to #{file}"
    rescue => e
      $status = "Failed to save to #{file}\n#{e.message}"
    end
  end
  Reline.pre_input_hook = -> do
    Reline.core.config.instance_eval do
      emacs = @additional_key_bindings[:emacs]
      emacs.add("\C-s".bytes, :_editor_save)
      emacs.add("\r".bytes, :key_newline)
    end
    if File.exist?(file)
      code = File.read(file)
      Reline.line_editor.instance_variable_set(:@buffer_of_lines, code.split("\n"))
    end
  end
  if file =~ /\.rb$/
    Reline.output_modifier_proc = ->(output, complete:) do
      IRB::Color.colorize_code(output, complete: complete, local_variables: [])
    end
    Reline.auto_indent_proc = ->(lines, line_index, byte_pointer, is_newline) do
      return nil if lines == [nil] # Workaround for exit IRB with CTRL+d
      return nil if !is_newline && lines[line_index]&.byteslice(0, byte_pointer)&.match?(/\A\s*\z/)

      code = lines[0..line_index].map { |l| "#{l}\n" }.join
      tokens = RubyLex.ripper_lex_without_warning(code, local_variables: [])
      RubyLex.new.process_indent_level(tokens, lines, line_index, is_newline)
    end
  end
  begin
    Reline.readmultiline { false }
  rescue Interrupt
  end
end

file = ARGV[0]
unless file
  puts 'file=ARGV[0] missing'
  exit
end
puts "Editing file #{file}"
puts 'Save: C-s'
puts 'Exit: C-c'
puts
edit file