ruby_poro_active_model.rb

class Base
  include ActiveModel::Model
  extend ActiveModel::Callbacks
  attr_accessor :id

  # https://stackoverflow.com/questions/17681789/rails-what-is-a-proper-way-to-include-callbacks-into-tableless-model
  define_model_callbacks :save, :create

  ALL = []

  def initialize(params = {})
    run_callbacks :create do
      super
    end
  end

  class << self
    def first
      all.first
    end
    
    def last
      all.last
    end

    def all
      ALL.select{|el| el.is_a?(self) }
    end

    def create(params = {})
      model = self.new(params)
      model.save
      model
    end

    def delete(object)
      all.reject!{|el| el.id.eql?(object) }

      all.each do |el|
        r_el = el.id.eql?(object)
        all.delete_at(all.index{|x| x.id.eql? object }) if r_el
      end
    end

    def update(object, params = {})
      el = all.detect{|el| el.id.eql?(object)}
      el.update_record(params) if el
    end
  end

  def persisted?
    id ? true : false
  end

  def attributes
    instance_variables.map{|el| [el.to_s.tr('@',''), instance_variable_get(el.to_s)] }.to_h
  end
  
  def save
    run_callbacks :save do
      return false unless valid?
      
      add if id.nil?
      true
    end
  end

  def add
    @id = self.class.all.size + 1
    ALL << self
  end

  def update_record(params)
    self.attributes = params
    save
  end
end


class Account < Base
  include ActiveModel::Validations::Callbacks
  validates :name, :email, :country, :language, :timezone,  presence: true
  validates_inclusion_of :language, in: ['en','es']
  validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i, allow_blank: true


  ATTRS = %i[name email country language timezone id]
  attr_accessor(*ATTRS)
  
  class << self
    ATTRS.each do |key|
      define_method("find_by_#{key}") do |arg|
        all.select{|el| el.send(key).eql?(arg) }
      end
    end
  end

  def users
    User.all.select{|el| el.account_id.eql?(id) }
  end
end

class User < Base
  include ActiveModel::Validations::Callbacks
  validates :name, :email, :account_id, presence: true

  ATTRS = %i[name email account_id]
  attr_accessor(*ATTRS)
  
  before_save :valid_account


  def valid_account
    raise Exception.new 'Account must be exists' if Account.find_by_id(account_id).empty?
  end

  def account
    Account.find_by_id(account_id)
  end
end