Bridge

# Implementors: the "how". Each terminal knows only how to write coloured text.
class AnsiTerminal
  COLOURS = { yellow: 33, red: 31 }.freeze

  def write(text, colour:) = "\e[#{COLOURS.fetch(colour)}m#{text}\e[0m"
end

class PlainTerminal
  def write(text, colour:) = text
end

# The Abstraction: the "what". It holds a terminal and talks to it through
# the terminal's interface, never its class.
class Panel
  def initialize(terminal)
    @terminal = terminal
  end

  def render
    @terminal.write(text, colour:)
  end

  private

  def text
    raise NotImplementedError, "#{self.class} must define #text"
  end

  def colour = :yellow
end

# Refined Abstractions vary independently of the terminals.
class PurseLine < Panel
  def initialize(terminal, gold:)
    super(terminal)
    @gold = gold
  end

  private

  def text = "Gold: #{@gold}"
end

class WaveBanner < Panel
  def initialize(terminal, wave:)
    super(terminal)
    @wave = wave
  end

  private

  def text = "~ Wave #{@wave} ~"
  def colour = :red
end