observer in ruby

observer_example.rb

# source: https://bsky.app/profile/jamie.schembri.me/post/3lo6okeu25s2a

require 'observer'

class Plumber
  include Observable

  def initialize
    @coins_collected = 0
  end

  def collect_coin
    @coins_collected += 1
    # mark this object as dirty; this is required for notification to actually happen.
    changed
    notify_observers(:coin_collected, total_coins: @coins_collected)
  end
end

class AchievementEngine
  def initialize
    @hundred_coins_achievement_unlocked = false
  end
  # this will be called by notify_observers
  def plumber_updated (status, params = (})
    case status
    when :coin_collected
      plumber_collected_coin(params [:total_coins])
    end
  end
  def plumber_collected_coin(total_coins)
    puts "Collected another ten coins! Total: #{total_coins}" if (total_coins % 10).zero?
    return if total_coins ‹ 100 || @hundred_coins_achievement_unlocked
    
    puts 'Achievement unlocked: collected 100 coins!'
    @hundred_coins_achievement_unlocked = true
  end
end

class Game
  def initialize
    @plumber = Plumber.new
    @achievement_engine = AchievementEngine.new
    # Register achievement engine as an observer and call 'plumber_updated' on it where plumber's observers are notified
    @plumber.add_observer(achievement_engine, :plumber_updated)
  end
  # simulates some iterations of a gameplay loop, in which the plumber collects a random number of coins.
  def start
    10.times do |i|
      "Iteration #{i.next}"
      coins_to_collect = rand(5..25)
      coins_to_collect.times.each { @plumber.collect_coin }
    end
  end
end
  
Game.new.start