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? Specifically wanting to reduce the number of lines of codes.

if num_length < 8
  tracking_service = false
else
  if number[1, 1] == 'Z'
    tracking_service = 'ups'
  elsif number[0, 1] == 'Q'
    tracking_service = 'dhl'
  elsif number[0, 2] == '96' && num_length == 22
    tracking_service = 'fedex'
  elsif number[0, 1] == 'H' && num_length == 11
    tracking_service = 'ups'
  elsif number[0, 1] == 'K' && num_length == 11
    tracking_service = 'ups'
  elsif num_length == 18 || num_length == 20
    check_response(number)
  else
    case num_length
    when 17
      tracking_service = 'dhlgm'
    when 13,20,22,30
      tracking_service = 'usps'
    when 12,15,19
      tracking_service = 'fedex'
    when 10,11
      tracking_service = 'dhl'
    else
      tracking_service = false  
    end  
  end
end

Yes, I know. It's nasty.

Answer 1

Try this. I rewrote it using case and regular expressions. I also used :symbols instead of "strings" for the return values, but you can change that back.

tracking_service = case number
  when /^.Z/ then :ups
  when /^Q/ then :dhl
  when /^96.{20}$/ then :fedex
  when /^[HK].{10}$/ then :ups
else
  check_response(number) if num_length == 18 || num_length == 20
  case num_length
    when 17 then :dhlgm
    when 13, 20, 22, 30 then :usps
    when 12, 15, 19 then :fedex
    when 10, 11 then :dhl
    else false
  end
end

Answer 2

Depending on whether or not the tracking code is a ruby object, you could also put helper's in it's class definition:

class TrackingCode < String 
  # not sure if this makes sense for your use case
  def ups?
    self[1,1] == 'Z'
  end
  def dhl?
    self[0,1] == 'Q'
  end
  def fedex?
    self.length == 22 && self[0, 2] == '96'
  end
  # etc...
end

Then your conditional becomes:

if number.ups?
  # ...
elsif number.dhl?
  # ...
elseif number.fedex?
end

One simplified conditional where you are operating on the implied feature of the tracking code. Likewise, if you were to take a looping approach, your loop would also be cleaner:

%w(ups? dhl? fedex?).each do |is_code|
  return if number.send(is_code)
end

or even:

%w(ups? dhl? fedex?).each do |is_code|
  yield if number.send(is_code)
end