gistfile1.txt

# From within a Arel compiler we'd like to call #invert_directions(orders)
# to reverse the order of all the order clauses

def invert_direction_value(str)
  case str
    when  /\bDESC\b/i     then str.gsub!(/\bDESC\b/i, "ASC")
    when  /\bASC\b/i      then str.gsub!(/\bASC\b/i, "DESC")
  end
  str
end

def invert_direction(ordering)
  if ordering.is_a?(Arel::Value)
    invert_direction_value(ordering.value)
  elsif ordering.is_a?(Arel::SqlLiteral)
    invert_direction_value(ordering)
  elsif ordering.is_a? Arel::Ordering
    ordering.is_a?(Arel::Ascending) ? Arel::Descending.new(ordering.attribute) : Arel::Ascending.new(ordering.attribute)
  end
end

def invert_directions(orderings)
  orderings.map do |ordering|
    invert_direction(ordering)
  end
end