module Ass
  class Parser
    
    OPEN_BRACE = " {\n"
    CLOSING_BRACE = "}\n"
    
    AT = /^ *@/
    COMMENT = /^ *\/\*(.*)(?:\*\/)?$/
    ASS_COMMENT = /&\/\//
    BLANK = /^ *$/ # TODO: Single \n char as well, update test.ass
    WORD = /([\w]+)/
    HYPHENATED_WORD = /([\w\-]+)/
    MIXIN = /^ *\+#{WORD}/
    SELECTOR = /^([#\w\-\.,:\[\]\~\* ]+) *$/ # TODO: review CSS specification
    EQUALS = / *= */
    CONSTANT = /:#{WORD}/
    CONSTANT_VALUE = /([#\w]+)/
    CONSTANT_WITH_VALUE = /^ *#{CONSTANT}#{EQUALS}#{CONSTANT_VALUE}/
    PROPERTY = /^ *#{HYPHENATED_WORD}/
    
    attr_accessor :ass, :constants, :css
    alias :to_s :css
    
    def initialize ass = ''
      @ass, @css, @constants = ass, '', {}
    end
    
    def parse!
      mixins = Hash.new ''
      in_block, in_mixin = false, false
      last_selector = ''
      lines = @ass.split "\n"
      lines.each do |line|
        
        case line
        when COMMENT
          @css << "/* #{$1.strip} */\n"
        when MIXIN
          if in_block
            next if in_mixin
            @css << mixins[$1]
          else
            in_mixin, in_block = $1, true
          end
        when CONSTANT_WITH_VALUE
          @constants[$1.to_sym] = $2
        when BLANK
          if in_block
            in_block = false
            next if in_mixin
            @css << CLOSING_BRACE
          end
        when AT
          @css << line << "\n"
        else
          if not in_block and line.match SELECTOR 
            in_block = true
            if nested_selector?($1, last_selector)
              next if in_mixin
              selector = splice_selectors last_selector, $1.strip
              @css << selector << OPEN_BRACE
            else
              in_mixin = false
              selector = $1.strip
              @css << selector << OPEN_BRACE
            end
            last_selector = selector
          elsif line.match PROPERTY
            if mixin = in_mixin
              mixins[mixin] << format_property(line)
            else
              @css << format_property(line)
            end
          end
        end
      end
      self
    end
    
    def splice_selectors selector_a, selector_b
      selector_b[0,0] = ' ' unless selector_b[0,1] == ':'
      selector_a.strip.gsub(/([^,]+),/, "\\1#{selector_b},") << selector_b
    end
    
    def nested_selector? selector_a, selector_b
      indents_in(selector_a) > indents_in(selector_b)
    end
    
    def indents_in string
      string.match(/^( *)/).captures.first.length / 2 rescue 0
    end
    
    def format_property line
      line.gsub! PROPERTY, '  \1:'
      line.gsub! CONSTANT do |constant| 
        constant[0,1] = ''
        @constants[constant.to_sym] || 'undefined_constant'
      end
      line << ";\n"
    end
    
    def self.parse ass
      new(ass).parse!.css
    end
    
    def self.parse_file file
      new(File.read(file)).parse!.css
    end
    
  end
end