choose.rb

require_relative '../finite_automata/fa_rule'
require_relative '../finite_automata/nfa_design'
require_relative '../finite_automata/nfa_rulebook'
require_relative 'pattern'

class Choose < Struct.new(:first, :second)
  include Pattern

  def to_s
    [first, second].map { |pattern| pattern.bracket(precedence) }.join('|')
  end

  def precedence
    0
  end

  def to_nfa_design
    first_nfa_design = first.to_nfa_design
    second_nfa_design = second.to_nfa_design

    start_state = Object.new
    accept_states = first_nfa_design.accept_states + second_nfa_design.accept_states
    rules = first_nfa_design.rulebook.rules + second_nfa_design.rulebook.rules
    extra_rules = [first_nfa_design, second_nfa_design].map { |nfa_design|
      FARule.new(start_state, nil, nfa_design.start_state)
    }
    rulebook = NFARulebook.new(rules + extra_rules)

    NFADesign.new(start_state, accept_states, rulebook)
  end
end