module Gherkin
  module Parser
    class ParseError < StandardError
      def initialize(state, new_state, expected_states, line)
        super("Parse error on line #{line}. Found #{new_state} when expecting one of: #{expected_states.join(', ')}. (Current state: #{state}).")
      end
    end

    class Parser
      require 'gherkin/java_impl'
      java_impl('gherkin.jar')

      # Initialize the parser. +machine_name+ refers to a state machine table.
      def initialize(listener, raise_on_error=true, machine_name='root')
        @listener = listener
        @raise_on_error = raise_on_error
        @machines = []
        @machine_name = machine_name
        push_machine(@machine_name)
      end

      # Doesn't yet fall back to super
      def method_missing(method, *args)
        # TODO: Catch exception and call super
        if(event(method.to_s, args[-1]))
          @listener.send(method, *args)
        end
        if method == :eof
          pop_machine
          push_machine(@machine_name)
        end
      end

      def event(ev, line)
        machine.event(ev, line) do |state, expected|
          if @raise_on_error
            raise ParseError.new(state, ev, expected, line)
          else
            @listener.syntax_error(state, ev, expected, line)
            return false
          end
        end
        true
      end

      def push_machine(name)
        @machines.push(Machine.new(self, name))
      end

      def pop_machine
        @machines.pop
      end

      def machine
        @machines[-1]
      end

      def expected
        machine.expected
      end

      def force_state(state)
        machine.instance_variable_set('@state', state)
      end

      class Machine
        def initialize(parser, name)
          @parser = parser
          @name = name
          @transition_map = transition_map(name)
          @state = name
        end

        def event(ev, line)
          states = @transition_map[@state]
          raise "Unknown state: #{@state.inspect} for machine #{@name}" if states.nil?
          new_state = states[ev]
          case new_state
          when "E"
            yield @state, expected
          when /push\((.+)\)/
            @parser.push_machine($1)
            @parser.event(ev, line)
          when "pop()"
            @parser.pop_machine()
            @parser.event(ev, line)
          else
            raise "Unknown transition: #{ev.inspect} among #{states.inspect} for machine #{@name}" if new_state.nil?
            @state = new_state
          end
        end

        def expected
          allowed = @transition_map[@state].find_all { |_, action| action != "E" }
          allowed.collect { |state| state[0] }.sort - ['eof']
        end

        private

        @@transition_maps = {}

        def transition_map(name)
          @@transition_maps[name] ||= build_transition_map(name)
        end

        def build_transition_map(name)
          table = transition_table(name)
          events = table.shift[1..-1]
          table.inject({}) do |machine, actions|
            state = actions.shift
            machine[state] = Hash[*events.zip(actions).flatten]
            machine
          end
        end

        def transition_table(name)
          state_machine_reader = StateMachineReader.new
          lexer = Gherkin::I18n.new('en').lexer(state_machine_reader)
          lexer.scan(File.read(File.dirname(__FILE__) + "/#{name}.txt"))
          state_machine_reader.rows
        end

        class StateMachineReader
          attr_reader :rows

          def initialize
            @rows = []
          end

          def row(row, line_number)
            @rows << row
          end

          def eof
          end
        end

      end
    end
  end
end