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

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

Answer 2

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 3

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 4

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 5

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).