require 'sass'

module SCSSLint
  class Linter::ShorthandLinter < Linter
    include LinterRegistry

    def visit_prop(node)
      unless SHORTHANDABLE_PROPERTIES.include? node.name.first.to_s
        return
      end

      if node.value.to_sass.strip =~ /\A(\S+\s+\S+(\s+\S+){0,2})\Z/
        add_lint(node) unless valid_shorthand?($1)
      end
    end

    def description
      'Property values should use the shortest shorthand syntax allowed'
    end

  private

    SHORTHANDABLE_PROPERTIES = %w[border-color
                                  border-radius
                                  border-style
                                  border-width
                                  margin
                                  padding]

    def valid_shorthand?(shorthand)
      values = shorthand.split(/\s+/)
      top, right, bottom, left = values

      if top == right && right == bottom && bottom == left
        false
      elsif top == right && bottom.nil? && left.nil?
        false
      elsif top == bottom && right == left
        false
      elsif top == bottom && left.nil?
        false
      elsif right == left
        false
      else
        true
      end
    end
  end
end