1 00:00:02,120 --> 00:00:03,450 The problem we have 2 00:00:03,450 --> 00:00:04,890 with processPayment and processRefund is 3 00:00:06,450 --> 00:00:09,600 that we have some kind of code duplication in there. 4 00:00:09,600 --> 00:00:12,220 We have the same kind of checks, which we run in there 5 00:00:12,220 --> 00:00:14,070 and that's bad because that means 6 00:00:14,070 --> 00:00:17,270 that we repeat ourselves, which we of course shouldn't do 7 00:00:17,270 --> 00:00:18,103 as we learned. 8 00:00:19,100 --> 00:00:20,810 The problem just is that 9 00:00:20,810 --> 00:00:24,310 for these different checks, we then do different things. 10 00:00:24,310 --> 00:00:26,556 We processCreditCardPayments 11 00:00:26,556 --> 00:00:29,810 and CreditCardRefunds, which are different functions 12 00:00:29,810 --> 00:00:32,460 which of course that should be easy to imagine, 13 00:00:32,460 --> 00:00:35,300 do totally different things in reality. 14 00:00:35,300 --> 00:00:36,730 Here, we just log something 15 00:00:36,730 --> 00:00:39,620 to the console, but that's just some dummy code. 16 00:00:39,620 --> 00:00:40,453 In reality, 17 00:00:40,453 --> 00:00:43,810 there's a big difference between charging a credit card 18 00:00:43,810 --> 00:00:46,950 and refunding a payment to the credit card. 19 00:00:46,950 --> 00:00:50,060 So it makes sense that we have different functions here 20 00:00:50,060 --> 00:00:52,870 and we probably won't be able to merge these 21 00:00:52,870 --> 00:00:54,470 in an elegant way. 22 00:00:54,470 --> 00:00:57,270 Though there actually is something we could 23 00:00:57,270 --> 00:01:00,320 consider doing to slim this code 24 00:01:00,320 --> 00:01:02,440 down and to make it more readable. 25 00:01:02,440 --> 00:01:07,400 We could kind of inverse our checking logic. 26 00:01:07,400 --> 00:01:09,010 Now, what do I mean by that? 27 00:01:09,010 --> 00:01:12,530 Currently we first check whether we have a payment 28 00:01:12,530 --> 00:01:15,630 or a refund, and then we process this payment 29 00:01:15,630 --> 00:01:18,670 or a refund, which means we then have these checks. 30 00:01:18,670 --> 00:01:20,530 Of course we could theoretically 31 00:01:20,530 --> 00:01:23,930 also first check what the payment method is, 32 00:01:23,930 --> 00:01:26,450 since we have the same methods for both payments 33 00:01:26,450 --> 00:01:30,080 and refunds, and then only check if it's a payment or refund 34 00:01:30,080 --> 00:01:33,790 in the second step. To check this, I will actually get rid 35 00:01:33,790 --> 00:01:36,810 of checking for his payment and his refund, though, 36 00:01:36,810 --> 00:01:38,670 I will keep these functions 37 00:01:38,670 --> 00:01:41,670 but instead I'll add a new function where I wanna check 38 00:01:41,670 --> 00:01:45,420 whether a transaction uses credit card, PayPal 39 00:01:45,420 --> 00:01:46,683 or a payment plan. 40 00:01:47,640 --> 00:01:50,280 So we can name this function usesCreditCard 41 00:01:52,100 --> 00:01:54,683 and we would get a transaction here. 42 00:01:55,690 --> 00:01:59,993 And then I wanna essentially return this check here. 43 00:02:00,920 --> 00:02:05,920 So I have return transaction method equals credit card 44 00:02:07,040 --> 00:02:10,360 and we can repeat this function to 45 00:02:10,360 --> 00:02:15,110 also have a usesPayPal function, where we check 46 00:02:15,110 --> 00:02:20,110 for PayPal as a method and to have a usesPlan function 47 00:02:21,140 --> 00:02:25,453 where we check for plan as a payment method. 48 00:02:26,330 --> 00:02:29,010 We could even merge these together 49 00:02:29,010 --> 00:02:34,010 and just have a usesTransactionMethod function 50 00:02:34,170 --> 00:02:37,020 where we get the transaction and the method. 51 00:02:37,020 --> 00:02:39,400 And we then have this comparison here. 52 00:02:39,400 --> 00:02:40,233 It's up to you, 53 00:02:40,233 --> 00:02:43,990 which approach you prefer. With such a method added though, 54 00:02:43,990 --> 00:02:46,400 we could go to processTransaction 55 00:02:46,400 --> 00:02:48,930 and not check first, whether it's a payment 56 00:02:48,930 --> 00:02:52,400 or a refund, but instead, simply check 57 00:02:52,400 --> 00:02:55,043 if he usesTransactionMethod 58 00:02:55,980 --> 00:02:57,260 for any given transaction. 59 00:02:57,260 --> 00:02:59,853 For example, if we use credit card, 60 00:03:00,900 --> 00:03:04,570 and if we do that, then we'll do something here. 61 00:03:04,570 --> 00:03:08,150 Else, if we use the another method 62 00:03:08,150 --> 00:03:13,150 let's say PayPal, we do something else. 63 00:03:13,860 --> 00:03:16,010 And last but not least 64 00:03:16,010 --> 00:03:21,010 if we have a transaction where the method is plan, 65 00:03:22,550 --> 00:03:24,773 we do get something else. 66 00:03:25,610 --> 00:03:29,080 Now, what are these something else's which you wanna do? 67 00:03:29,080 --> 00:03:31,340 Well, that is now our processing 68 00:03:31,340 --> 00:03:33,220 for credit card transactions, 69 00:03:33,220 --> 00:03:36,133 PayPal transactions, and plan transactions. 70 00:03:37,160 --> 00:03:40,200 So these would be new functions, which we can add. 71 00:03:40,200 --> 00:03:43,800 We can add a new function here, maybe above processPayment 72 00:03:43,800 --> 00:03:47,090 which is named processCreditCardTransaction. 73 00:03:50,130 --> 00:03:52,400 And here we get our transaction, no matter 74 00:03:52,400 --> 00:03:56,070 if it's a payment or a refund and we can do the same 75 00:03:56,070 --> 00:03:59,210 for PayPal to have a processPayPalTransaction 76 00:04:00,930 --> 00:04:03,430 and the same for a payment plan. 77 00:04:03,430 --> 00:04:04,680 So processPlanTransaction 78 00:04:07,300 --> 00:04:10,490 and we'll add logic to these functions in a second. 79 00:04:10,490 --> 00:04:12,410 So now we have these free functions 80 00:04:12,410 --> 00:04:15,490 and these are the functions which we wanna call here. 81 00:04:15,490 --> 00:04:19,300 So we wanna process a credit card transaction here 82 00:04:19,300 --> 00:04:22,410 and forward the transaction in the next 83 00:04:22,410 --> 00:04:25,853 if branch, we wanna processPayPalTransaction 84 00:04:29,300 --> 00:04:32,040 and forward the transaction. 85 00:04:32,040 --> 00:04:35,767 And in the last branch, we wanna processPlanTransaction 86 00:04:36,810 --> 00:04:39,163 and forward the transaction like this. 87 00:04:40,360 --> 00:04:42,280 Now we will eventually remove this code. 88 00:04:42,280 --> 00:04:45,140 I'll just leave it here for reference for a second. 89 00:04:45,140 --> 00:04:47,020 But now we have these functions 90 00:04:47,020 --> 00:04:50,960 which are being called depending on the transaction method. 91 00:04:50,960 --> 00:04:52,900 So to check, which we previously had instead 92 00:04:52,900 --> 00:04:56,310 of processPayment and processRefund now moved 93 00:04:56,310 --> 00:04:59,183 up one level directly into processTransaction. 94 00:05:00,940 --> 00:05:03,620 Therefore, to fully invert our logic, 95 00:05:03,620 --> 00:05:05,570 we now have to move the payment 96 00:05:05,570 --> 00:05:08,120 and refund logic down one level 97 00:05:08,120 --> 00:05:11,860 out of processTransaction into these processCreditCard, 98 00:05:11,860 --> 00:05:15,100 PayPal and planTransaction functions. 99 00:05:15,100 --> 00:05:17,440 Hence now in all these functions, 100 00:05:17,440 --> 00:05:20,350 we have to check whether we have a payment or a refund. 101 00:05:20,350 --> 00:05:23,550 And that is what I meant with, we invert the logic. 102 00:05:23,550 --> 00:05:25,680 We will still have some duplication. 103 00:05:25,680 --> 00:05:26,513 There is no way 104 00:05:26,513 --> 00:05:30,340 around that because we had two dependent kind if checks. 105 00:05:30,340 --> 00:05:32,350 But now we have the more complex 106 00:05:32,350 --> 00:05:36,530 if check where we replicated three different checks 107 00:05:36,530 --> 00:05:37,950 at a higher level. 108 00:05:37,950 --> 00:05:40,010 And we have the easier check where 109 00:05:40,010 --> 00:05:42,930 we only have queue options at a lower level. 110 00:05:42,930 --> 00:05:43,763 But on the other hand, 111 00:05:43,763 --> 00:05:45,920 we execute this check three times now. 112 00:05:45,920 --> 00:05:49,230 So overall, we can question whether we gain a lot. 113 00:05:49,230 --> 00:05:52,300 Nonetheless, let's finish this before we look for an 114 00:05:52,300 --> 00:05:53,863 even more elegant solution. 115 00:05:54,830 --> 00:05:58,750 So here, in processCreditCardTransaction, we can now check 116 00:05:58,750 --> 00:06:02,620 if we have a payment using this is payment function 117 00:06:02,620 --> 00:06:04,200 which we defined before, 118 00:06:04,200 --> 00:06:09,200 for our given transaction, or if we have a refund 119 00:06:10,210 --> 00:06:15,210 for this given transaction or else we know it's invalid 120 00:06:15,450 --> 00:06:17,580 and then we can show an error message 121 00:06:17,580 --> 00:06:21,560 and simply, well, use this code 122 00:06:21,560 --> 00:06:25,320 from before, show error message, invalid transaction type 123 00:06:25,320 --> 00:06:29,450 and pass the transaction as well, like this. 124 00:06:29,450 --> 00:06:30,283 And now, 125 00:06:30,283 --> 00:06:33,290 if it's a payment, we know it's a credit card payment. 126 00:06:33,290 --> 00:06:35,363 So here we can call processCreditCardPayment. 127 00:06:36,941 --> 00:06:37,774 And that's one 128 00:06:37,774 --> 00:06:39,800 of the functions which existed right from the start. 129 00:06:39,800 --> 00:06:41,323 One of these dummy functions. 130 00:06:42,200 --> 00:06:45,530 If it's a refund, we know it's a credit card refund, 131 00:06:45,530 --> 00:06:48,580 so we can call processCreditCardRefund. 132 00:06:48,580 --> 00:06:50,310 And now we can copy that code 133 00:06:50,310 --> 00:06:53,300 into the other method functions here. 134 00:06:53,300 --> 00:06:55,230 So here we call processPayPalPayment 135 00:06:58,030 --> 00:07:02,270 and processPayPalRefund. 136 00:07:02,270 --> 00:07:04,520 And here we have processPlanPayment 137 00:07:07,022 --> 00:07:08,855 and processPlanRefund. 138 00:07:11,093 --> 00:07:11,926 And we can now get rid 139 00:07:11,926 --> 00:07:14,690 of processPayment and processRefund down there 140 00:07:14,690 --> 00:07:17,053 because we don't need these functions anymore. 141 00:07:18,010 --> 00:07:21,420 So what we did now is we inverted these checks. 142 00:07:21,420 --> 00:07:22,770 Now we check for the method 143 00:07:22,770 --> 00:07:25,870 at a higher level, and then for the type of transaction 144 00:07:25,870 --> 00:07:28,500 at a lower level, hence we can now remove this 145 00:07:28,500 --> 00:07:32,150 if check here from the process transaction function 146 00:07:32,150 --> 00:07:33,900 because that's the check which we now have 147 00:07:33,900 --> 00:07:37,030 in all these methods, specific functions. 148 00:07:37,030 --> 00:07:39,520 Nonetheless, of course we have duplication here 149 00:07:39,520 --> 00:07:42,300 and just like this, we also won't be able to get rid 150 00:07:42,300 --> 00:07:45,400 of it because we're in the interest of moving around checks. 151 00:07:45,400 --> 00:07:46,470 And it's up to you, 152 00:07:46,470 --> 00:07:49,590 which kind of solution you find easier to read. 153 00:07:49,590 --> 00:07:51,620 If it was the one from before 154 00:07:51,620 --> 00:07:54,950 where we had the payment refund check at a higher level 155 00:07:54,950 --> 00:07:57,720 and we checked for the method at a lower level, 156 00:07:57,720 --> 00:08:01,550 or if it's this solution where we do the opposite. 157 00:08:01,550 --> 00:08:03,680 Nonetheless, this is our current state 158 00:08:03,680 --> 00:08:05,883 which we will now use to build up on.