grammar Less
  rule primary
    (declaration / ruleset / import / comment)+ <Builder> / declaration* <Builder> / import* <Builder> / comment*
  end
  
  rule comment
    ws '/*' (!'*/' . )* '*/' ws / ws '//' (!"\n" .)* "\n" ws
  end
  
  #
  # div, .class, body > p {...}
  #
  rule ruleset
    selectors "{" ws primary ws "}" ws {
      def build env
        # Build the ruleset for each selector
        selectors.build(env, :ruleset).each do |sel|
          primary.build sel
        end
      end
    } / ws selectors ';' ws {
      def build env        
        selectors.build(env, :mixin).each do |path|
          rules = path.inject(env.root) do |current, node|
            current.descend(node.selector, node) or raise MixinNameError, path.join
          end.rules
          env.rules += rules
        end
      end
    }
  end
  
  rule import
    "@import" S url:(string / url) medias? s ';' ws {
      def build env
        path = File.join(env.root.file, url.value)
        path += '.less' unless path =~ /\.less$/
        if File.exist? path
          imported = Less::Engine.new(File.new path).to_tree
          env.rules += imported.rules
        else
          raise ImportError, path
        end
      end
    }
  end
  
  rule url
    'url(' path:(string / [-a-zA-Z0-9_%$/.&=:;#+?]+) ')' {
      def build env = nil
        Node::String.new(CGI.unescape path.text_value)
      end
      
      def value
        build
      end
    }
  end
  
  rule medias
    [-a-z]+ (s ',' s [a-z]+)*
  end
  
  rule selectors
    ws selector tail:(s ',' ws selector)* ws {
      def build env, method 
        all.map do |e|
          e.send(method, env) if e.respond_to? method
        end.compact
      end
      
      def all
        [selector] + tail.elements.map {|e| e.selector }
      end
    }
  end
  
  #
  # div > p a {...}
  #
  rule selector
    (s select element s)+ arguments? {
      def ruleset env
        elements.inject(env) do |node, e|
          node << Node::Element.new(e.element.text_value, e.select.text_value)
          node.last
        end
      end
      
      def mixin env
        elements.map do |e|
          Node::Element.new(e.element.text_value, e.select.text_value)
        end
      end
    }
  end
  
  #
  # @my-var: 12px;
  # height: 100%;
  #
  rule declaration
    ws name:(ident / variable) s ':' s expression s (';'/ ws &'}') ws {
      def build env
        env << (name.text_value =~ /^@/ ? Node::Variable : Node::Property).new(name.text_value, [])
        expression.build env
      end
    # Empty rule
    } / ws ident s ':' s ';' ws
  end
  
  #
  # An operation or compound value
  #
  rule expression
    entity (operator / S / WS) expression <Builder> / entity
  end
  
  #
  # Entity: Any whitespace delimited token
  #
  rule entity
    function / fonts / keyword / accessor / variable / literal / important
  end
  
  rule fonts
    font family:(s ',' s font)+ {
      def build env
        fonts = ([font] + family.elements.map {|f| f.font }).map do |font|
          font.build env
        end
        env.identifiers.last << Node::FontFamily.new(fonts)
      end
    }
  end
  
  rule font
    [a-zA-Z] [-a-zA-Z0-9]* {
      def build env
        Node::Keyword.new(text_value)
      end
    } / string {
      def build env
        Node::String.new(text_value)
      end
    }
  end
  
  #
  # An identifier
  #
  rule ident
    '-'? [-a-z0-9_]+
  end
  
  rule variable
    '@' [-a-zA-Z0-9_]+  {
      def build env
        env.identifiers.last << Node::Variable.new(text_value)
      end
    }
  end
  
  #
  # div / .class / #id / input[type="text"] / lang(fr)
  #
  rule element
    (class_id / tag / ident) attribute* ('(' ident? attribute* ')')? / attribute+ / '@media' / '@font-face'
  end
  
  rule class_id
    tag? (class / id)+
  end
  
  #
  # [type="text"]
  #
  rule attribute
    '[' tag ([|~*$^]? '=') (tag / string) ']' / '[' (tag / string) ']'
  end
  
  rule class
    '.' [_a-z] [-a-zA-Z0-9_]*
  end
  
  rule id
    '#' [_a-z] [-a-zA-Z0-9_]*
  end
  
  rule tag
    [a-zA-Z] [-a-zA-Z]* [0-9]? / '*'
  end
  
  rule select
    (s [+>~] s / s ':' / S)?
  end
  
  # TODO: Merge this with attribute rule
  rule accessor
    ident:(class_id / tag) '[' attr:(string / variable) ']' {
      def build env
        env.identifiers.last << env.nearest(ident.text_value)[attr.text_value.delete(%q["'])].evaluate
      end
    }
  end
  
  rule operator
    S [-+*/] S {
      def build env
        env.identifiers.last << Node::Operator.new(text_value.strip)
      end
    } / [-+*/] {
      def build env
        env.identifiers.last << Node::Operator.new(text_value)
      end
    }
  end
  
  #
  # Tokens which don't need to be evaluated
  #
  rule literal
    color / (dimension / [-a-z]+) '/' dimension {
      def build env
        env.identifiers.last << Node::Anonymous.new(text_value)
      end
    } / number unit {
      def build env
        env.identifiers.last << Node::Number.new(number.text_value, unit.text_value)
      end
    } / string {
      def build env
        env.identifiers.last << Node::String.new(text_value)
      end
    }
  end
  
  # !important
  rule important
    '!important' {
      def build env
        env.identifiers.last << Node::Keyword.new(text_value)
      end
    }
  end
  
  #
  # `blue`, `small`, `normal` etc.
  #
  rule keyword
    [-a-zA-Z]+ !ns {
      def build env
        env.identifiers.last << Node::Keyword.new(text_value)
      end
    }
  end
    
  #
  # 'hello world' / "hello world"
  #
  rule string
    "'" content:(!"'" . )* "'" {
      def value
        text_value[1...-1]
      end
    } / ["] content:(!["] . )* ["] {
      def value
        text_value[1...-1]
      end
    }
  end
  
  #
  # Numbers & Units
  #
  rule dimension
    number unit
  end
  
  rule number
    '-'? [0-9]* '.' [0-9]+ / '-'? [0-9]+
  end
  
  rule unit
    ('px'/'em'/'pc'/'%'/'pt'/'cm'/'mm')?
  end

  
  #
  # Color
  #
  rule color
    '#' rgb {
      def build env
        env.identifiers.last << Node::Color.new(*rgb.build)
      end
    } / fn:(('hsl'/'rgb') 'a'?) arguments {
      def build env
        env.identifiers.last << Node::Function.new(fn.text_value, arguments.build.flatten)
      end
    }
  end
  
  #
  # 00ffdd / 0fd
  #
  rule rgb
    r:(hex hex) g:(hex hex) b:(hex hex) {
      def build
        [r.text_value, g.text_value, b.text_value]
      end
    } / r:hex g:hex b:hex {
      def build
        [r.text_value, g.text_value, b.text_value].map {|c| c * 2 }
      end
    }
  end
  
  rule hex
    [a-fA-F0-9]
  end
      
  #
  # Functions and arguments
  #
  rule function
    name:([-a-zA-Z_]+) arguments {
      def build env
        env.identifiers.last << Node::Function.new(name.text_value, [arguments.build].flatten)
      end
    }
  end
  
  rule arguments
    '(' s argument s tail:(',' s argument s)* ')' {
      def build
        all.map do |e|
          e.build if e.respond_to? :build
        end.compact
      end
    
      def all
        [argument] + tail.elements.map {|e| e.argument }
      end
    }
  end
  
  rule argument
    color {
      def build
        Node::Color.new text_value
      end
    } / number unit {
      def build
        Node::Number.new number.text_value, unit.text_value
      end
    } / string {
      def build
        Node::String.new text_value
      end
    } / [a-zA-Z]+ '=' dimension {
      def build
        Node::Anonymous.new text_value
      end
    } / [-a-zA-Z0-9_%$/.&=:;#+?]+ {
      def build
        Node::String.new text_value
      end
    }
  end
  
  #
  # Whitespace
  #
  rule s
    [ ]*
  end
  
  rule S
    [ ]+
  end
  
  rule ws
    [\n ]*
  end
  
  rule WS
    [\n ]+
  end
  
  # Non-space char
  rule ns
    ![ ;\n] .
  end
end