module Sprite
  module Sass
    module Extensions
      def sprite_background(group, image)
        sprite = sprite_data(group, image)
        if sprite
          sprite_path = sprite_builder.image_path(group.value)
          "url('#{sprite_path}') no-repeat #{sprite[:x]}px #{sprite[:y]}px"
        else
          ""
        end
      end

      def sprite_width(*args)
        sprite_attr(:width, *args)
      end

      def sprite_height(*args)
        sprite_attr(:height, *args)
      end

      def sprite_x_offset(*args)
        sprite_attr(:x, *args)
      end

      def sprite_y_offset(*args)
        sprite_attr(:y, *args)
      end

      def sprite_image(group)
        sprite_builder.image_path(group.value)
      end

      def sprite_url(group)
        "url('#{sprite_image(group)}')"
      end

      def sprite_offset(group, image, x=nil, y=nil)
        x ||= sprite_x_offset(group, image)
        y ||= sprite_y_offset(group, image)
        "#{x} #{y}"
      end

    protected
      def sprite_attr(attr, group, image)
        sprite = sprite_data(group, image)
        if sprite
          "#{sprite[attr]}px"
        else
          ""
        end
      end

      def sprite_builder
        @__sprite_builder ||= Builder.from_config
      end

      def sprite_data(group, image)
        unless @__sprite_data
          sprite_data_path = sprite_builder.style_output_path

          # read sprite data from yml
          @__sprite_data = File.open(sprite_data_path) { |yf| YAML::load( yf ) }
        end

        group_data = @__sprite_data[group.to_s]
        if group_data
          return group_data[image.to_s]
        else
          nil
        end
      end
    end
  end
end

if defined?(Sass)
  module Sass::Script::Functions
    include Sprite::Sass::Extensions
  end
end