Help refactoring this nasty Ruby if/else statement - ruby-on-rails

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

Answer 3

This method looks like it was written for speed. You can use a minhash as a substitute, but I think the code is fairly clean and doesn't require a refactor. Rubyists tend to be disgusted by needless structure, but oftentimes it's needed to model real-world situations and/or provides a performance boost. The keyword should be needless.

Answer 4

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).

Answer 5

I believe this is sufficiently complex to deserve its own method.
BTW, if the length is 20 then the original function returns whatever check_response(n) returns, yet then attempts (and will always fail) to return 'usps'.
#lenMap = Hash.new false
#lenMap[17] = 'dhlgm'
#lenMap[13] = #lenMap[20] = #lenMap[22] = #lenMap[30] = 'usps'
#lenMap[12] = #lenMap[15] = #lenMap[19] = 'fedex'
#lenMap[10] = #lenMap[11] = 'dhl'
def ts n
len = n.length
return false if len < 8
case n
when /^.Z/
return 'ups'
when /^Q/
return 'dhl'
when /^96....................$/
return 'fedex'
when /^[HK]..........$/
return 'ups'
end
return check_response n if len == 18 or len == 20
return #lenMap[len]
end
# test code...
def check_response n
return 'check 18/20 '
end
%w{ 1Zwhatever Qetcetcetc 9634567890123456789012 H2345678901
K2345678901 hownowhownowhownow hownowhownowhownow90
12345678901234567
1234567890123
12345678901234567890
1234567890123456789012
123456789012345678901234567890
123456789012
123456789012345
1234567890123456789
1234567890
12345678901 }.each do |s|
puts "%32s %s" % [s, (ts s).to_s]
end