Convert 15 digit Salesforce ID to 18 digit Salesforce ID

Convert Salesforce Id

# convert 15 digit SFDC ID to 18 digit
  def convert_salesforce_id(id)
    if id.try(:length) == 15
      chunks = id.chars.to_a
      char_map = %w{A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5}
      extension = []
      chunks.each_slice(5) { |x| y = x.reverse.map {|c| (c.match /[A-Z]/) ? 1 : 0 }.join("").to_i(2) ; extension << y}
      id = id + (extension.map {|e| char_map.at(e)}).join("").to_s
    end
    id
  end