require 'set'

class NFA
    attr_reader :alphabet

    @transitions = Hash.new

    def initialize(file)
        @filename = file

        File.open(file).each_with_index do |line, number|
            parse(line, number)
        end
    end

    def transition_function(state, symbol)
        @transitions[[state, symbol]]
    end

    private
    def parse(line, number)

        temp_array = line.strip.split(', ').map{|e| e.to_sym}
        tokens = Set.new

        if (temp_array.uniq == temp_array)
            tokens = Set.new temp_array
        else
            parse_error("Does not form a set", number) unless temp_array.uniq == tokens
        end

        #This method parses lines differently based on where they are in the file, as per the format
        #specificed in the assignment. Keep in mind thatthat "number" starts at 0.
        #
        #   0. alphabet, or input symbols
        #   1. NFA states
        #   2. starting states - which of course should be a singleton
        #   3. the set of all final or accepting states
        #
        #   All sequent lines represent transition functions
        case number
        when 0
            @alphabet = tokens
        when 1
            @states = tokens
        when 2
            if (tokens.length != 1) then
                parse_error "More than one start state in input file.", line
            elsif (not tokens.proper_subset? @states)
                parse_error "The start state is not a state of the DFA", line
            else
                @start_state = tokens
            end
        when 3
            if(not tokens.proper_subset? @states) then
                parse error "Final states are not a subset of the accepting states", line
            else
                @accepting_states = tokens
            end
        else
            @transitions[temp_array[0, 1]] = temp_array[2]
        end
    end

    def parse_error(msg, number)
        raise "line #{number}, #{@filename}\n #{msg}"
    end
end