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#
# The GoF Abstract Factory pattern
# written by Matthieu Tanguay-Carel
#
# Factories behave in effect like singletons.
# Extra functionality can be tested for with "Object#respond_to? :extra" 
# if needed (See GTKFactory).
#
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

module MyAbstractFactory
    def create_button
        raise NotImplementedError, "You should implement this method"
    end
end

class Win95Factory
    include MyAbstractFactory
    def create_button
        puts "I'm Win95"
        "win95button"
    end
end

class MotifFactory
    include MyAbstractFactory
    def create_button
        puts "I'm Motif"
        "motifbutton"
    end
end

class GTKFactory
    include MyAbstractFactory
    def create_button
        puts "I'm GTK"
        "gtkbutton"
    end

    def extra
        puts "I'm enhanced"
    end
end

class LookAndFeelManager

    @@types2classes = { 
        :motif => [MotifFactory,nil],
        :gtk   => [GTKFactory,nil],
        :win95 => [Win95Factory,nil]
    }

    def self.create type
        if !@@types2classes.include? type
            raise NotImplementedError, "I know nothing about type: #{type}"
        end
        factory_and_instance = @@types2classes[type]

        if factory_and_instance[1].nil?
            puts 'instantiating new factory'
            factory_and_instance[1] = factory_and_instance[0].new #mutex this
        else
            puts 'returning already instantiated factory'
            factory_and_instance[1]
        end
    end
end

if __FILE__ == $0
    factory = LookAndFeelManager.create :gtk
    puts factory.create_button
    factory.extra if factory.respond_to? :extra
end