class DFA < Struct.new(:current_state, :accept_states, :rulebook)
	def accepting?
		puts accept_states.include?(current_state)
	end
	def read_character(character)
		self.current_state = rulebook.next_state(current_state, character)
	end
	def read_string(string)
		string.chars.each do |character|
			read_character(character)
		end
	end
end

class DFADesign < Struct.new(:start_state, :accept_states, :rulebook)
	def to_dfa
		DFA.new(start_state, accept_states, rulebook)
	end
	def accepts?(string)
		#tap evaluates the block and returns object it was called on
		to_dfa.tap{ |dfa| dfa.read_string(string) }.accepting?
	end
end


class FARule < Struct.new(:state, :character, :next_state)
	def applies_to?(state, character)
		self.state == state && self.character == character
	end

	def follow
		next_state
	end

	def inspect
		"#<FARule #{state.inspect } -- #{character} --> #{next_state.inspect}>"
	end

end



class DFARulebook < Struct.new(:rules)
	def next_state(state, character)
   		rule_for(state, character).follow
	end

	def rule_for(state, character)
		if rules.detect{ |rule| rule.applies_to?(state, character) } == nil
			rules.push(FARule.new(state, character, state))
			rules.detect{ |rule| rule.applies_to?(state, character) }
		else
			rules.detect{ |rule| rule.applies_to?(state, character) }
	end
end