Help refactoring this nasty Ruby if/else statement

Question

So I have this big, hairy if/else statement. I pass a tracking number to it, and then it determines what type of tracking number it is.

How can I simplify this thing? Sp

Answer 1

Whilst longer than jtbandes solution, you might like this as it's a bit more declarative:

class Condition
  attr_reader :service_name, :predicate

  def initialize(service_name, &block)
    @service_name = service_name
    @predicate = block
  end
end

CONDITIONS = [
  Condition.new('ups')   { |n| n[1] == 'Z' },
  Condition.new('dhl')   { |n| n[0] == 'Q' },
  Condition.new('fedex') { |n| n[0..1] == '96' && n.size == 22 },
  Condition.new('ups')   { |n| n[0] == 'H' && n.size == 11 },
  Condition.new('ups')   { |n| n[0] == 'K' && n.size == 11 },
  Condition.new('dhlgm') { |n| n.size == 17 },
  Condition.new('usps')  { |n| [13, 20, 22, 30].include?(n.size) },
  Condition.new('fedex') { |n| [12, 15, 19].include?(n.size) },
  Condition.new('dhl')   { |n| [10, 11].include?(n.size) },
]

def tracking_service(tracking_number)
  result = CONDITIONS.find do |condition|
    condition.predicate.call(tracking_number)
  end

  result.service_name if result
end

I haven't dealt with the check_response method call here as I feel you should probably handle that elsewhere (assuming it does something other than return a tracking service name).