require 'strscan'

module Haml
  module Precompiler
    # Designates an XHTML/XML element.
    ELEMENT         = ?%

    # Designates a <tt><div></tt> element with the given class.
    DIV_CLASS       = ?.

    # Designates a <tt><div></tt> element with the given id.
    DIV_ID          = ?#

    # Designates an XHTML/XML comment.
    COMMENT         = ?/

    # Designates an XHTML doctype or script that is never HTML-escaped.
    DOCTYPE         = ?!

    # Designates script, the result of which is output.
    SCRIPT          = ?=

    # Designates script that is always HTML-escaped.
    SANITIZE        = ?&

    # Designates script, the result of which is flattened and output.
    FLAT_SCRIPT     = ?~

    # Designates script which is run but not output.
    SILENT_SCRIPT   = ?-

    # When following SILENT_SCRIPT, designates a comment that is not output.
    SILENT_COMMENT  = ?#

    # Designates a non-parsed line.
    ESCAPE          = ?\\

    # Designates a block of filtered text.
    FILTER          = ?:

    # Designates a non-parsed line. Not actually a character.
    PLAIN_TEXT      = -1

    # Keeps track of the ASCII values of the characters that begin a
    # specially-interpreted line.
    SPECIAL_CHARACTERS   = [
      ELEMENT,
      DIV_CLASS,
      DIV_ID,
      COMMENT,
      DOCTYPE,
      SCRIPT,
      SANITIZE,
      FLAT_SCRIPT,
      SILENT_SCRIPT,
      ESCAPE,
      FILTER
    ]

    # The value of the character that designates that a line is part
    # of a multiline string.
    MULTILINE_CHAR_VALUE = ?|

    # Characters that designate that a multiline string may be about
    # to begin.
    MULTILINE_STARTERS   = SPECIAL_CHARACTERS - [?/]

    # Keywords that appear in the middle of a Ruby block with lowered
    # indentation. If a block has been started using indentation,
    # lowering the indentation  with one of these won't end the block.
    # For example:
    #
    #   - if foo
    #     %p yes!
    #   - else
    #     %p no!
    #
    # The block is ended after <tt>%p no!</tt>, because <tt>else</tt>
    # is a member of this array.
    MID_BLOCK_KEYWORDS   = ['else', 'elsif', 'rescue', 'ensure', 'when']

    # The Regex that matches a Doctype command.
    DOCTYPE_REGEX = /(\d\.\d)?[\s]*([a-z]*)/i

    # The Regex that matches a literal string or symbol value
    LITERAL_VALUE_REGEX = /^\s*(:(\w*)|(('|")([^\\\#'"]*?)\4))\s*$/

    private

    # Returns the precompiled string with the preamble and postamble
    def precompiled_with_ambles(local_names)
      preamble = <<END.gsub("\n", ";")
extend Haml::Helpers
_hamlout = @haml_buffer = Haml::Buffer.new(@haml_buffer, #{options_for_buffer.inspect})
_erbout = _hamlout.buffer
END
      postamble = <<END.gsub("\n", ";")
@haml_buffer = @haml_buffer.upper
_erbout
END
      preamble + locals_code(local_names) + @precompiled + postamble
    end

    def locals_code(names)
      names = names.keys if Hash == names

      names.map do |name|
        "#{name} = _haml_locals[#{name.to_sym.inspect}] || _haml_locals[#{name.to_s.inspect}]"
      end.join(';') + ';'
    end

    Line = Struct.new(:text, :unstripped, :index, :spaces, :tabs)

    def precompile
      old_line = Line.new
      @template.split(/\r\n|\r|\n/).each_with_index do |text, index|
        @next_line = line = Line.new(text.strip, text.lstrip.chomp, index)
        line.spaces, line.tabs = count_soft_tabs(text)

        if line.text.empty? && !flat?
          newline
          next
        end

        suppress_render = handle_multiline(old_line) unless flat?

        if old_line.text.nil? || suppress_render
          old_line = line
          resolve_newlines
          newline
          next
        end

        process_indent(old_line) unless old_line.text.empty?

        if flat?
          push_flat(old_line)
          old_line = line
          newline
          next
        end

        if old_line.spaces != old_line.tabs * 2
          raise SyntaxError.new(<<END.strip, old_line.index)
#{old_line.spaces} space#{old_line.spaces == 1 ? ' was' : 's were'} used for indentation. Haml must be indented using two spaces.
END
        end

        unless old_line.text.empty? || @haml_comment
          process_line(old_line.text, old_line.index, line.tabs > old_line.tabs && !line.text.empty?)
        end
        resolve_newlines

        if !flat? && line.tabs - old_line.tabs > 1
          raise SyntaxError.new(<<END.strip, line.index)
#{line.spaces} spaces were used for indentation. Haml must be indented using two spaces.
END
        end
        old_line = line
        newline
      end

      # Close all the open tags
      close until @to_close_stack.empty?
      flush_merged_text
    end

    # Processes and deals with lowering indentation.
    def process_indent(line)
      return unless line.tabs <= @template_tabs && @template_tabs > 0

      to_close = @template_tabs - line.tabs
      to_close.times { |i| close unless to_close - 1 - i == 0 && mid_block_keyword?(line.text) }
    end

    # Processes a single line of Haml.
    #
    # This method doesn't return anything; it simply processes the line and
    # adds the appropriate code to <tt>@precompiled</tt>.
    def process_line(text, index, block_opened)
      @block_opened = block_opened
      @index = index + 1

      case text[0]
      when DIV_CLASS, DIV_ID; render_div(text)
      when ELEMENT; render_tag(text)
      when COMMENT; render_comment(text[1..-1].strip)
      when SANITIZE
        return push_script(unescape_interpolation(text[3..-1].strip), false, false, false, true) if text[1..2] == "=="
        return push_script(text[2..-1].strip, false, false, false, true) if text[1] == SCRIPT
        push_plain text
      when SCRIPT
        return push_script(unescape_interpolation(text[2..-1].strip), false) if text[1] == SCRIPT
        return push_script(text[1..-1], false, false, false, true) if options[:escape_html]
        push_script(text[1..-1], false)
      when FLAT_SCRIPT; push_flat_script(text[1..-1])
      when SILENT_SCRIPT
        return start_haml_comment if text[1] == SILENT_COMMENT

        push_silent(text[1..-1], true)
        newline_now
        if (@block_opened && !mid_block_keyword?(text)) || text[1..-1].split(' ', 2)[0] == "case"
          push_and_tabulate([:script])
        end
      when FILTER; start_filtered(text[1..-1].downcase)
      when DOCTYPE
        return render_doctype(text) if text[0...3] == '!!!'
        return push_script(unescape_interpolation(text[3..-1].strip), false) if text[1..2] == "=="
        return push_script(text[2..-1].strip, false) if text[1] == SCRIPT
        push_plain text
      when ESCAPE; push_plain text[1..-1]
      else push_plain text
      end
    end

    # Returns whether or not the text is a silent script text with one
    # of Ruby's mid-block keywords.
    def mid_block_keyword?(text)
      text.length > 2 && text[0] == SILENT_SCRIPT && MID_BLOCK_KEYWORDS.include?(text[1..-1].split[0])
    end

    # Deals with all the logic of figuring out whether a given line is
    # the beginning, continuation, or end of a multiline sequence.
    #
    # This returns whether or not the line should be
    # rendered normally.
    def handle_multiline(line)
      text = line.text

      # A multiline string is active, and is being continued
      if is_multiline?(text) && @multiline
        @multiline.text << text[0...-1]
        return true
      end

      # A multiline string has just been activated, start adding the lines
      if is_multiline?(text) && (MULTILINE_STARTERS.include? text[0])
        @multiline = Line.new text[0...-1], nil, line.index, nil, line.tabs
        process_indent(line)
        return true
      end

      # A multiline string has just ended, make line into the result
      if @multiline && !line.text.empty?
        process_line(@multiline.text, @multiline.index, line.tabs > @multiline.tabs)
        @multiline = nil
      end

      return false
    end

    # Checks whether or not +line+ is in a multiline sequence.
    def is_multiline?(text)
      text && text.length > 1 && text[-1] == MULTILINE_CHAR_VALUE && text[-2] == ?\s
    end

    # Evaluates <tt>text</tt> in the context of the scope object, but
    # does not output the result.
    def push_silent(text, can_suppress = false)
      flush_merged_text
      return if can_suppress && options[:suppress_eval]
      @precompiled << "#{text};"
    end

    # Adds <tt>text</tt> to <tt>@buffer</tt> with appropriate tabulation
    # without parsing it.
    def push_merged_text(text, tab_change = 0, indent = true)
      @merged_text  << (!indent || @dont_indent_next_line || @options[:ugly] ? text : "#{'  ' * @output_tabs}#{text}")
      @dont_indent_next_line = false
      @tab_change   += tab_change
    end

    # Concatenate <tt>text</tt> to <tt>@buffer</tt> without tabulation.
    def concat_merged_text(text)
      @merged_text  << text
    end

    def push_text(text, tab_change = 0)
      push_merged_text("#{text}\n", tab_change)
    end

    def flush_merged_text
      return if @merged_text.empty?

      @precompiled  << "_hamlout.push_text(#{@merged_text.dump}"
      @precompiled  << ", #{@dont_tab_up_next_text.inspect}" if @dont_tab_up_next_text || @tab_change != 0
      @precompiled  << ", #{@tab_change}" if @tab_change != 0
      @precompiled  << ");"
      @merged_text   = ''
      @dont_tab_up_next_text = false
      @tab_change    = 0
    end

    # Renders a block of text as plain text.
    # Also checks for an illegally opened block.
    def push_plain(text)
      if @block_opened
        raise SyntaxError.new("Illegal nesting: nesting within plain text is illegal.", @next_line.index)
      end

      push_text text
    end

    # Adds +text+ to <tt>@buffer</tt> while flattening text.
    def push_flat(line)
      unless @options[:ugly]
        tabulation = line.spaces - @flat_spaces
        tabulation = tabulation > -1 ? tabulation : 0
        @filter_buffer << "#{' ' * tabulation}#{line.unstripped}\n"
      else
        @filter_buffer << "#{line.unstripped}\n"
      end
    end

    # Causes <tt>text</tt> to be evaluated in the context of
    # the scope object and the result to be added to <tt>@buffer</tt>.
    #
    # If <tt>preserve_script</tt> is true, Haml::Helpers#find_and_flatten is run on
    # the result before it is added to <tt>@buffer</tt>
    def push_script(text, preserve_script, in_tag = false, preserve_tag = false,
                    escape_html = false, nuke_inner_whitespace = false)
      # Prerender tabulation unless we're in a tag
      push_merged_text '' unless in_tag

      flush_merged_text
      return if options[:suppress_eval]

      raise SyntaxError.new("There's no Ruby code for = to evaluate.") if text.empty?

      push_silent "haml_temp = #{text}"
      newline_now
      args = [preserve_script, in_tag, preserve_tag,
              escape_html, nuke_inner_whitespace].map { |a| a.inspect }.join(', ')
      out = "haml_temp = _hamlout.push_script(haml_temp, #{args});"
      if @block_opened
        push_and_tabulate([:loud, out])
      else
        @precompiled << out
      end
    end

    # Causes <tt>text</tt> to be evaluated, and Haml::Helpers#find_and_flatten
    # to be run on it afterwards.
    def push_flat_script(text)
      flush_merged_text

      raise SyntaxError.new("There's no Ruby code for ~ to evaluate.") if text.empty?
      push_script(text, true)
    end

    def start_haml_comment
      return unless @block_opened

      @haml_comment = true
      push_and_tabulate([:haml_comment])
    end

    # Closes the most recent item in <tt>@to_close_stack</tt>.
    def close
      tag, value = @to_close_stack.pop
      case tag
      when :script; close_block
      when :comment; close_comment value
      when :element; close_tag value
      when :loud; close_loud value
      when :filtered; close_filtered value
      when :haml_comment; close_haml_comment
      end
    end

    # Puts a line in <tt>@precompiled</tt> that will add the closing tag of
    # the most recently opened tag.
    def close_tag(value)
      tag, nuke_outer_whitespace, nuke_inner_whitespace = value
      @output_tabs -= 1 unless nuke_inner_whitespace
      @template_tabs -= 1
      rstrip_buffer! if nuke_inner_whitespace
      push_merged_text("</#{tag}>" + (nuke_outer_whitespace ? "" : "\n"),
                       nuke_inner_whitespace ? 0 : -1, !nuke_inner_whitespace)
      @dont_indent_next_line = nuke_outer_whitespace
    end

    # Closes a Ruby block.
    def close_block
      push_silent "end", true
      @template_tabs -= 1
    end

    # Closes a comment.
    def close_comment(has_conditional)
      @output_tabs -= 1
      @template_tabs -= 1
      close_tag = has_conditional ? "<![endif]-->" : "-->"
      push_text(close_tag, -1)
    end

    # Closes a loud Ruby block.
    def close_loud(command)
      push_silent 'end', true
      @precompiled << command
      @template_tabs -= 1
    end

    # Closes a filtered block.
    def close_filtered(filter)
      @flat_spaces = -1
      filter.internal_compile(self, @filter_buffer)
      @filter_buffer = nil
      @template_tabs -= 1
    end

    def close_haml_comment
      @haml_comment = false
      @template_tabs -= 1
    end

    # Iterates through the classes and ids supplied through <tt>.</tt>
    # and <tt>#</tt> syntax, and returns a hash with them as attributes,
    # that can then be merged with another attributes hash.
    def parse_class_and_id(list)
      attributes = {}
      list.scan(/([#.])([-_a-zA-Z0-9]+)/) do |type, property|
        case type
        when '.'
          if attributes['class']
            attributes['class'] += " "
          else
            attributes['class'] = ""
          end
          attributes['class'] += property
        when '#'; attributes['id'] = property
        end
      end
      attributes
    end

    def parse_literal_value(text)
      return nil unless text
      text.match(LITERAL_VALUE_REGEX)

      # $2 holds the value matched by a symbol, but is nil for a string match
      # $5 holds the value matched by a string
      $2 || $5
    end

    def parse_static_hash(text)
      return {} unless text

      attributes = {}
      text.split(',').each do |attrib|
        key, value, more = attrib.split('=>')

        # Make sure the key and value and only the key and value exist
        # Otherwise, it's too complicated or dynamic and we'll defer it to the actual Ruby parser
        key = parse_literal_value key
        value = parse_literal_value value
        return nil if more || key.nil? || value.nil?

        attributes[key] = value
      end
      attributes
    end

    # This is a class method so it can be accessed from Buffer.
    def self.build_attributes(is_html, attr_wrapper, attributes = {})
      quote_escape = attr_wrapper == '"' ? "&quot;" : "&apos;"
      other_quote_char = attr_wrapper == '"' ? "'" : '"'

      result = attributes.collect do |attr, value|
        next if value.nil?

        if value == true
          next " #{attr}" if is_html
          next " #{attr}=#{attr_wrapper}#{attr}#{attr_wrapper}"
        elsif value == false
          next
        end

        value = Haml::Helpers.escape_once(value.to_s)
        # We want to decide whether or not to escape quotes
        value.gsub!('&quot;', '"')
        this_attr_wrapper = attr_wrapper
        if value.include? attr_wrapper
          if value.include? other_quote_char
            value = value.gsub(attr_wrapper, quote_escape)
          else
            this_attr_wrapper = other_quote_char
          end
        end
        " #{attr}=#{this_attr_wrapper}#{value}#{this_attr_wrapper}"
      end
      result.compact.sort.join
    end

    def prerender_tag(name, self_close, attributes)
      attributes_string = Precompiler.build_attributes(html?, @options[:attr_wrapper], attributes)
      "<#{name}#{attributes_string}#{self_close && xhtml? ? ' /' : ''}>"
    end

    # Parses a line into tag_name, attributes, attributes_hash, object_ref, action, value
    def parse_tag(line)
      raise SyntaxError.new("Invalid tag: \"#{line}\".") unless match = line.scan(/%([-:\w]+)([-\w\.\#]*)(.*)/)[0]
      tag_name, attributes, rest = match
      attributes_hash, rest = parse_attributes(rest) if rest[0] == ?{
      if rest
        object_ref, rest = balance(rest, ?[, ?]) if rest[0] == ?[
        attributes_hash, rest = parse_attributes(rest) if rest[0] == ?{ && attributes_hash.nil?
        nuke_whitespace, action, value = rest.scan(/(<>|><|[><])?([=\/\~&!])?(.*)?/)[0]
        nuke_whitespace ||= ''
        nuke_outer_whitespace = nuke_whitespace.include? '>'
        nuke_inner_whitespace = nuke_whitespace.include? '<'
      end
      value = value.to_s.strip
      [tag_name, attributes, attributes_hash, object_ref, nuke_outer_whitespace,
       nuke_inner_whitespace, action, value]
    end

    def parse_attributes(line)
      scanner = StringScanner.new(line)
      attributes_hash, rest = balance(scanner, ?{, ?})
      attributes_hash = attributes_hash[1...-1] if attributes_hash
      return attributes_hash, rest
    end

    # Parses a line that will render as an XHTML tag, and adds the code that will
    # render that tag to <tt>@precompiled</tt>.
    def render_tag(line)
      tag_name, attributes, attributes_hash, object_ref, nuke_outer_whitespace,
        nuke_inner_whitespace, action, value = parse_tag(line)

      raise SyntaxError.new("Illegal element: classes and ids must have values.") if attributes =~ /[\.#](\.|#|\z)/

      # Get rid of whitespace outside of the tag if we need to
      rstrip_buffer! if nuke_outer_whitespace

      preserve_tag = options[:preserve].include?(tag_name)
      nuke_inner_whitespace ||= preserve_tag
      preserve_tag &&= !options[:ugly]

      case action
      when '/'; self_closing = xhtml?
      when '~'; parse = preserve_script = true
      when '='
        parse = true
        value = unescape_interpolation(value[1..-1].strip) if value[0] == ?=
      when '&', '!'
        if value[0] == ?=
          parse = true
          value = (value[1] == ?= ? unescape_interpolation(value[2..-1].strip) : value[1..-1].strip)
        end
      end

      if parse && @options[:suppress_eval]
        parse = false
        value = ''
      end

      escape_html = (action == '&' || (action != '!' && @options[:escape_html]))

      object_ref = "nil" if object_ref.nil? || @options[:suppress_eval]

      static_attributes = parse_static_hash(attributes_hash) # Try pre-compiling a static attributes hash
      attributes_hash = nil if static_attributes || @options[:suppress_eval]
      attributes = parse_class_and_id(attributes)
      Buffer.merge_attrs(attributes, static_attributes) if static_attributes

      raise SyntaxError.new("Illegal nesting: nesting within a self-closing tag is illegal.", @next_line.index) if @block_opened && self_closing
      raise SyntaxError.new("Illegal nesting: content can't be both given on the same line as %#{tag_name} and nested within it.", @next_line.index) if @block_opened && !value.empty?
      raise SyntaxError.new("There's no Ruby code for #{action} to evaluate.") if parse && value.empty?
      raise SyntaxError.new("Self-closing tags can't have content.") if self_closing && !value.empty?

      self_closing ||= !!( !@block_opened && value.empty? && @options[:autoclose].include?(tag_name) )

      dont_indent_next_line =
        (nuke_outer_whitespace && !@block_opened) ||
        (nuke_inner_whitespace && @block_opened)

      # Check if we can render the tag directly to text and not process it in the buffer
      if object_ref == "nil" && attributes_hash.nil? && !preserve_script
        tag_closed = !@block_opened && !self_closing && !parse

        open_tag  = prerender_tag(tag_name, self_closing, attributes)
        if tag_closed
          open_tag << "#{value}</#{tag_name}>"
          open_tag << "\n" unless nuke_outer_whitespace
        else
          open_tag << "\n" unless parse || nuke_inner_whitespace || (self_closing && nuke_outer_whitespace)
        end
        
        push_merged_text(open_tag, tag_closed || self_closing || nuke_inner_whitespace ? 0 : 1,
                         !nuke_outer_whitespace)

        @dont_indent_next_line = dont_indent_next_line
        return if tag_closed
      else
        flush_merged_text
        content = value.empty? || parse ? 'nil' : value.dump
        attributes_hash = ', ' + attributes_hash if attributes_hash
        args = [tag_name, self_closing, !@block_opened, preserve_tag, escape_html,
                attributes, nuke_outer_whitespace, nuke_inner_whitespace
               ].map { |v| v.inspect }.join(', ')
        push_silent "_hamlout.open_tag(#{args}, #{object_ref}, #{content}#{attributes_hash})"
        @dont_tab_up_next_text = @dont_indent_next_line = dont_indent_next_line
      end

      return if self_closing

      if value.empty?
        push_and_tabulate([:element, [tag_name, nuke_outer_whitespace, nuke_inner_whitespace]])
        @output_tabs += 1 unless nuke_inner_whitespace
        return
      end

      if parse
        flush_merged_text
        push_script(value, preserve_script, true, preserve_tag, escape_html, nuke_inner_whitespace)
        @dont_tab_up_next_text = true
        concat_merged_text("</#{tag_name}>" + (nuke_outer_whitespace ? "" : "\n"))
      end
    end

    # Renders a line that creates an XHTML tag and has an implicit div because of
    # <tt>.</tt> or <tt>#</tt>.
    def render_div(line)
      render_tag('%div' + line)
    end

    # Renders an XHTML comment.
    def render_comment(line)
      conditional, line = balance(line, ?[, ?]) if line[0] == ?[
      line.strip!
      conditional << ">" if conditional

      if @block_opened && !line.empty?
        raise SyntaxError.new('Illegal nesting: nesting within a tag that already has content is illegal.', @next_line.index)
      end

      open = "<!--#{conditional} "

      # Render it statically if possible
      unless line.empty?
        return push_text("#{open}#{line} #{conditional ? "<![endif]-->" : "-->"}")
      end

      push_text(open, 1)
      @output_tabs += 1
      push_and_tabulate([:comment, !conditional.nil?])
      unless line.empty?
        push_text(line)
        close
      end
    end

    # Renders an XHTML doctype or XML shebang.
    def render_doctype(line)
      raise SyntaxError.new("Illegal nesting: nesting within a header command is illegal.", @next_line.index) if @block_opened
      doctype = text_for_doctype(line)
      push_text doctype if doctype
    end

    def text_for_doctype(text)
      text = text[3..-1].lstrip.downcase
      if text.index("xml") == 0
        return nil if html?
        wrapper = @options[:attr_wrapper]
        return "<?xml version=#{wrapper}1.0#{wrapper} encoding=#{wrapper}#{text.split(' ')[1] || "utf-8"}#{wrapper} ?>"
      end

      if html5?
        '<!DOCTYPE html>'
      else
        version, type = text.scan(DOCTYPE_REGEX)[0]

        if xhtml?
          if version == "1.1"
            '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">'
          else
            case type
            when "strict";   '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">'
            when "frameset"; '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">'
            else             '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">'
            end
          end

        elsif html4?
          case type
          when "strict";   '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">'
          when "frameset"; '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">'
          else             '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">'
          end
        end
      end
    end

    # Starts a filtered block.
    def start_filtered(name)
      raise Error.new("Invalid filter name \":#{name}\".") unless name =~ /^\w+$/

      unless filter = Filters.defined[name]
        if filter == 'redcloth' || filter == 'markdown' || filter == 'textile'
          raise Error.new("You must have the RedCloth gem installed to use \"#{name}\" filter")
        end
        raise Error.new("Filter \"#{name}\" is not defined.")
      end

      push_and_tabulate([:filtered, filter])
      @flat_spaces = @template_tabs * 2
      @filter_buffer = String.new
      @block_opened = false
    end

    def contains_interpolation?(str)
      str.include?('#{')
    end

    def unescape_interpolation(str)
      scan = StringScanner.new(str.dump)
      str = ''

      while scan.scan(/(.*?)(\\+)\#\{/)
        escapes = (scan[2].size - 1) / 2
        str << scan.matched[0...-3 - escapes]
        if escapes % 2 == 1
          str << '#{'
        else
          # Use eval to get rid of string escapes
          str << '#{' + eval('"' + balance(scan, ?{, ?}, 1)[0][0...-1] + '"') + "}"
        end
      end

      str + scan.rest
    end

    def balance(scanner, start, finish, count = 0)
      str = ''
      scanner = StringScanner.new(scanner) unless scanner.is_a? StringScanner
      regexp = Regexp.new("(.*?)[\\#{start.chr}\\#{finish.chr}]")
      while scanner.scan(regexp)
        str << scanner.matched
        count += 1 if scanner.matched[-1] == start
        count -= 1 if scanner.matched[-1] == finish
        return [str.strip, scanner.rest] if count == 0
      end

      raise SyntaxError.new("Unbalanced brackets.")
    end

    # Counts the tabulation of a line.
    def count_soft_tabs(line)
      spaces = line.index(/([^ ]|$)/)
      if line[spaces] == ?\t
        return 0, 0 if line.strip.empty?
        raise SyntaxError.new(<<END.strip, @next_line.index)
A tab character was used for indentation. Haml must be indented using two spaces.
Are you sure you have soft tabs enabled in your editor?
END
      end
      [spaces, spaces/2]
    end

    # Pushes value onto <tt>@to_close_stack</tt> and increases
    # <tt>@template_tabs</tt>.
    def push_and_tabulate(value)
      @to_close_stack.push(value)
      @template_tabs += 1
    end

    def flat?
      @flat_spaces != -1
    end

    def newline
      @newlines += 1
    end

    def newline_now
      @precompiled << "\n"
      @newlines -= 1
    end

    def resolve_newlines
      return unless @newlines > 0
      @precompiled << "\n" * @newlines
      @newlines = 0
    end

    # Get rid of and whitespace at the end of the buffer
    # or the merged text
    def rstrip_buffer!
      unless @merged_text.empty?
        @merged_text.rstrip!
      else
        push_silent("_erbout.rstrip!", false)
        @dont_tab_up_next_text = true
      end
    end
  end
end