First Class Commands Ruby Notes

first_class_command_notes.rb

# https://raganwald.com/2016/01/19/command-pattern.html

class State
  attr_reader :history, :future
  attr_accessor :text

  def initialize(text)
    @history = []
    @future = []
    @text = text
  end

  def undo
    undoer = history.pop
    redoer = undoer.undo

    future.unshift(redoer)
    undoer.do
  end

  def redo
    redoer = future.shift
    undoer = redoer.undo

    history.push(undoer)
    redoer.do
  end

  def replace(replacement, from = 0, to = text.length)
    doer = Command.new(self, replacement, from, to)
    undoer = doer.undo

    history.push(undoer)
    @future = []

    doer.do
  end
end

class Command
  attr_reader :state, :replacement, :from, :to

  def initialize(state, replacement, from, to)
    @state = state
    @replacement = replacement
    @from = from
    @to = to
  end

  def inspect
    "Command<#{replacement}, #{from}, #{to}>"
  end

  def do
    puts "History: #{state.history}"
    puts "Future: #{state.future}"
    state.text = state.text.slice(0...from) + replacement + state.text.slice(to..)
    puts state.text
    state
  end

  def undo
    was_replaced = state.text.slice(from...to)
    Command.new(state, was_replaced, from, from + replacement.length)
  end
end

state = State.new("The quick brown fox jumped over the lazy dog")
puts state.text

state.replace("fast", 4, 9)
state.replace("canine", 40, 43)
state.undo
state.undo
state.redo
state.redo