module ShellOpts
  module Grammar
    class Lexer
      def self.lex(source)
        lines = source.split("\n").map(&:strip)

        # Skip initial blank lines
        lines = lines.drop_while { |line| line == "" }

        # Split lines into command, option, argument, or text
        res = []
        while line = lines.shift
          if line =~ SCAN_RE
            # Collect following comments
            txts = []
            while lines.first && lines.first !~ SCAN_RE
              txts << lines.shift
            end

            words = line.split(/\s+/)
            while word = words.shift
              type = 
                  case word
                    when OPTION_RE
                      "OPT"
                    when COMMAND_PATH_RE
                      "CMD"
                    when ARGUMENT_EXPR_RE
                      args = [word]
                      # Scan arguments
                      while words.first =~ ARGUMENT_EXPR_RE
                        args << words.shift
                      end
                      word = args.join(" ")
                      "ARG"
                    when /^[a-z0-9]/
                      raise CompileError, "Illegal argument: #{word} (should be uppercase)"
                    else
                      raise CompileError, "Illegal syntax: #{line}"
                  end
              res << [type, word]
              txts.each { |txt| res << ["TXT", txt] } # Add comments after first command or option
              txts = []
            end
          elsif line =~ /^-|\+/
            raise CompileError, "Illegal short option name: #{line}"
          else
            res << ["TXT", line]
          end
        end
        res
      end
    end
  end
end