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Scalate integration with JRuby to access Ruby based filters such as sass
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require 'sass/script/lexer'

module Sass
  module Script
    # The parser for SassScript.
    # It parses a string of code into a tree of {Script::Node}s.
    class Parser
      # The line number of the parser's current position.
      #
      # @return [Fixnum]
      def line
        @lexer.line
      end

      # @param str [String, StringScanner] The source text to parse
      # @param line [Fixnum] The line on which the SassScript appears.
      #   Used for error reporting
      # @param offset [Fixnum] The number of characters in on which the SassScript appears.
      #   Used for error reporting
      # @param options [{Symbol => Object}] An options hash;
      #   see {file:SASS_REFERENCE.md#sass_options the Sass options documentation}
      def initialize(str, line, offset, options = {})
        @options = options
        @lexer = lexer_class.new(str, line, offset, options)
      end

      # Parses a SassScript expression within an interpolated segment (`#{}`).
      # This means that it stops when it comes across an unmatched `}`,
      # which signals the end of an interpolated segment,
      # it returns rather than throwing an error.
      #
      # @return [Script::Node] The root node of the parse tree
      # @raise [Sass::SyntaxError] if the expression isn't valid SassScript
      def parse_interpolated
        expr = assert_expr :expr
        assert_tok :end_interpolation
        expr.options = @options
        expr
      rescue Sass::SyntaxError => e
        e.modify_backtrace :line => @lexer.line, :filename => @options[:filename]
        raise e
      end

      # Parses a SassScript expression.
      #
      # @return [Script::Node] The root node of the parse tree
      # @raise [Sass::SyntaxError] if the expression isn't valid SassScript
      def parse
        expr = assert_expr :expr
        assert_done
        expr.options = @options
        expr
      rescue Sass::SyntaxError => e
        e.modify_backtrace :line => @lexer.line, :filename => @options[:filename]
        raise e
      end

      # Parses a SassScript expression,
      # ending it when it encounters one of the given identifier tokens.
      #
      # @param [#include?(String)] A set of strings that delimit the expression.
      # @return [Script::Node] The root node of the parse tree
      # @raise [Sass::SyntaxError] if the expression isn't valid SassScript
      def parse_until(tokens)
        @stop_at = tokens
        expr = assert_expr :expr
        assert_done
        expr.options = @options
        expr
      rescue Sass::SyntaxError => e
        e.modify_backtrace :line => @lexer.line, :filename => @options[:filename]
        raise e
      end

      # Parses the argument list for a mixin include.
      #
      # @return [Array] The root nodes of the arguments.
      # @raise [Sass::SyntaxError] if the argument list isn't valid SassScript
      def parse_mixin_include_arglist
        args = []

        if try_tok(:lparen)
          args = arglist || args
          assert_tok(:rparen)
        end
        assert_done

        args.each {|a| a.options = @options}
        args
      rescue Sass::SyntaxError => e
        e.modify_backtrace :line => @lexer.line, :filename => @options[:filename]
        raise e
      end

      # Parses the argument list for a mixin definition.
      #
      # @return [Array] The root nodes of the arguments.
      # @raise [Sass::SyntaxError] if the argument list isn't valid SassScript
      def parse_mixin_definition_arglist
        args = defn_arglist!(false)
        assert_done

        args.each do |k, v|
          k.options = @options
          v.options = @options if v
        end
        args
      rescue Sass::SyntaxError => e
        e.modify_backtrace :line => @lexer.line, :filename => @options[:filename]
        raise e
      end

      # Parses a SassScript expression.
      #
      # @overload parse(str, line, offset, filename = nil)
      # @return [Script::Node] The root node of the parse tree
      # @see Parser#initialize
      # @see Parser#parse
      def self.parse(*args)
        new(*args).parse
      end

      PRECEDENCE = [
        :comma, :single_eq, :concat, :or, :and,
        [:eq, :neq],
        [:gt, :gte, :lt, :lte],
        [:plus, :minus],
        [:times, :div, :mod],
      ]

      ASSOCIATIVE = [:comma, :concat, :plus, :times]

      class << self
        # Returns an integer representing the precedence
        # of the given operator.
        # A lower integer indicates a looser binding.
        #
        # @private
        def precedence_of(op)
          PRECEDENCE.each_with_index do |e, i|
            return i if Array(e).include?(op)
          end
          raise "[BUG] Unknown operator #{op}"
        end

        # Returns whether or not the given operation is associative.
        #
        # @private
        def associative?(op)
          ASSOCIATIVE.include?(op)
        end

        private

        # Defines a simple left-associative production.
        # name is the name of the production,
        # sub is the name of the production beneath it,
        # and ops is a list of operators for this precedence level
        def production(name, sub, *ops)
          class_eval < "string",
        :default => "expression (e.g. 1px, bold)",
        :arglist => "mixin argument",
        :fn_arglist => "function argument",
      }

      def assert_expr(name)
        (e = send(name)) && (return e)
        @lexer.expected!(EXPR_NAMES[name] || EXPR_NAMES[:default])
      end

      def assert_tok(*names)
        (t = try_tok(*names)) && (return t)
        @lexer.expected!(names.map {|tok| Lexer::TOKEN_NAMES[tok] || tok}.join(" or "))
      end

      def try_tok(*names)
        peeked =  @lexer.peek
        peeked && names.include?(peeked.type) && @lexer.next
      end

      def assert_done
        return if @lexer.done?
        @lexer.expected!(EXPR_NAMES[:default])
      end

      def node(node)
        node.line = @lexer.line
        node
      end
    end
  end
end