superhero.rb

require 'active_model'

class Superhero
  include ActiveModel::Validations

  attr_accessor :name, :age

  def initialize **args
    @name = args[:name]

    @age = args[:age]
  end

  class << self
    def create **args
      new **args
    end

    def all
      ObjectSpace.each_object(self).to_a
    end

    def find_by **args
      all.select { |elem| elem if condition elem, **args  }
    end

    def condition elem, **args
      if args[:name] && args[:age]
          elem.name == args[:name] && elem.age == args[:age]
        elsif args[:name]
          elem.name == args[:name]
        elsif args[:age]
          elem.age == args[:age]
        end
      end
  end

  validates :age, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true

  validate :name_must_be_unique

  def name_must_be_unique
    if all_names.count(name) >= 2
     errors.add(:name, "the name: #{name} is already exists." )
   end
  end

  def all_names
    Superhero.all.map { |e| e.name }
  end
end


superhero1 = Superhero.create name: 'Bruce', age: 2
# p superhero1.valid?
# p superhero1.errors.messages
superhero2 = Superhero.create name: 'Bruce', age: 0
p superhero2.valid?
superhero3 = Superhero.create name: 'David', age: 21
superhero4 = Superhero.create name: 'James', age: 10
superhero5 = Superhero.create name: 'Bruce', age: 13
# p superhero5.valid?
# p superhero5.errors.messages
p Superhero.find_by name: 'Bruce'
# p Superhero.find_by age: 21
# p Superhero.find_by name: 'James', age: 12
# p superhero1.valid?
# p superhero1.errors.messages