module Less
  grammar StyleSheet
    include Common
    include Entity
    
    rule primary
      (declaration / ruleset / import / comment)* {
        def build env = Less::Element.new
          elements.map do |e|
            e.build env if e.respond_to? :build
          end; env
        end
      }
    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 =~ /\.(le|c)ss$/
          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
      sel:(s select element s)+ arguments? {
        def ruleset env
          sel.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
          sel.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 expressions s (';'/ ws &'}') ws {
        def build env
          env << (name.text_value =~ /^@/ ? 
            Node::Variable : Node::Property).new(name.text_value, expressions.build(env), env)
        end
      # Empty rule
      } / ws ident s ':' s ';' ws
    end

    #
    # An operation or compound value
    #
    rule expressions
      # Operation
      expression tail:(operator expression)+ {
        def build env 
          all.map {|e| e.build(env) }.dissolve
        end

        def all
          [expression] + tail.elements.map {|i| [i.operator, i.expression] }.flatten.compact
        end
      # Space-delimited expressions
      } / expression tail:(WS expression)* {
        def build env
          all.map {|e| e.build(env) if e.respond_to? :build }.compact
        end
        
        def all
          [expression] + tail.elements.map {|f| f.expression }
        end
      # Catch-all rule
      } / [-a-zA-Z0-9_%*/.&=:,#+? \[\]()]+ {
        def build env
          [Node::Anonymous.new(text_value)]
        end
      }
    end

    rule expression
      '(' s expressions s ')' {
        def build env
          Node::Expression.new(['('] + expressions.build(env).flatten + [')'])
        end
      } / entity '' {
        def build env
          entity.method(:build).arity.zero?? entity.build : entity.build(env)
        end
      }
    end

    #
    # An identifier
    #
    rule ident
      '*'? '-'? [-a-z0-9_]+
    end

    rule variable
      '@' [-a-zA-Z0-9_]+  {
        def build
          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-zA-Z] [-a-zA-Z0-9_]*
    end

    rule id
      '#' [_a-zA-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.nearest(ident.text_value)[attr.text_value.delete(%q["'])].evaluate
        end
      }
    end

    rule operator
      S [-+*/] S {
        def build env
          Node::Operator.new(text_value.strip)
        end
      } / [-+*/] {
        def build env
          Node::Operator.new(text_value)
        end
      }
    end
    
    #
    # Functions and arguments
    #
    rule function
      name:([-a-zA-Z_]+) arguments {
        def build
          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 / 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
      } / function / keyword other:(S keyword)* {
        def build
        end
      }
    end
  end
end