Sync Luhn with problem specifications (#199)

exercises/practice/luhn/.meta/config.json

@@ -5,7 +5,8 @@
   "contributors": [
     "adolfopa",
     "etrepum",
-    "yurrriq"
+    "yurrriq",
+    "kahgoh"
   ],
   "files": {
     "solution": [

exercises/practice/luhn/.meta/example.lfe

@@ -1,28 +1,30 @@
 (defmodule luhn
-  (export (valid? 1)
-          (create 1)
-          (checksum 1)))
+  (export (valid? 1))
+)
 
-(defun valid? (number) (== (rem (checksum number) 10) 0))
+(defun valid? (number)
+  (case (checksum (lists:reverse number) 0 0)
+    ((tuple 'ok count total) (when (> count 1)) (== (rem total 10) 0))
+    (_ 'false)
+  )
+)
 
-(defun create (number)
-  (lists:flatten `(,number ,(- #\: (rem (checksum (++ number "0")) 10)))))
+(defun checksum
+  (('() count total) (tuple 'ok count total))
+  (((cons 32 reversed-number) count total) (checksum reversed-number count total))
+  (((cons h reversed-number) count total)
+    (when (=< #\0 h) (=< h #\9))
+    (checksum reversed-number
+      (+ count 1)
+      (+ total (number-to-add count (- h #\0)))
+    )
+  )
+  ((_ count total) (tuple 'invalid count total))
+)
 
-(defun checksum (number)
-  (checksum
-    (lists:reverse
-      (lists:filter
-        (lambda (c)
-          (=< #\0 c #\9))
-        number))
-    'odd
-    0))
+(defun number-to-add
+  ((count digit) (when (== (rem count 2) 0)) digit)
+  ((_ digit) (when (< digit 5)) (* digit 2))
+  ((_ digit) (- (* digit 2) 9))
+)
 
-(defun checksum
-  ([() _ total] total)
-  ([(cons h reversed-number) 'odd total]
-   (checksum reversed-number 'even (- (+ total h) #\0)))
-  ([(cons h reversed-number) 'even total] (when (< h #\5))
-   (checksum reversed-number 'odd (+ total (* (- h #\0) 2))))
-  ([(cons h reversed-number) 'even total] (when (>= h #\5))
-   (checksum reversed-number 'odd (- (+ total (* (- h #\0) 2)) 9))))

exercises/practice/luhn/.meta/tests.toml

@@ -33,6 +33,9 @@ description = "invalid credit card"
 [20e67fad-2121-43ed-99a8-14b5b856adb9]
 description = "invalid long number with an even remainder"
 
+[7e7c9fc1-d994-457c-811e-d390d52fba5e]
+description = "invalid long number with a remainder divisible by 5"
+
 [ad2a0c5f-84ed-4e5b-95da-6011d6f4f0aa]
 description = "valid number with an even number of digits"
 
@@ -57,6 +60,12 @@ description = "more than a single zero is valid"
 [ab56fa80-5de8-4735-8a4a-14dae588663e]
 description = "input digit 9 is correctly converted to output digit 9"
 
+[b9887ee8-8337-46c5-bc45-3bcab51bc36f]
+description = "very long input is valid"
+
+[8a7c0e24-85ea-4154-9cf1-c2db90eabc08]
+description = "valid luhn with an odd number of digits and non zero first digit"
+
 [39a06a5a-5bad-4e0f-b215-b042d46209b1]
 description = "using ascii value for non-doubled non-digit isn't allowed"
 

exercises/practice/luhn/src/luhn.app.src

@@ -1,6 +1,6 @@
 %% -*- erlang -*-
 {application, 'luhn',
- [{description, ""},
+ [{description, "Given a number determine whether or not it is valid per the Luhn formula."},
   {vsn, "0.0.1"},
   {modules,
    ['luhn']},

exercises/practice/luhn/src/luhn.lfe

@@ -0,0 +1,5 @@
+(defmodule luhn
+  (export (valid? 1))
+)
+
+; Please implement the `valid?` function.

exercises/practice/luhn/test/luhn-tests.lfe

@@ -4,14 +4,68 @@
 
 (include-lib "ltest/include/ltest-macros.lfe")
 
-(deftest invalid
-  (is-not (luhn:valid? "1111"))
-  (is-not (luhn:valid? "738")))
+(deftest single-digit-strings-can-not-be-valid
+  (is-not (luhn:valid? "1")))
 
-(deftest valid
-  (is (luhn:valid? "8739567"))
-  (is (luhn:valid? "8763"))
-  (is (luhn:valid? "2323 2005 7766 3554")))
+(deftest a-single-zero-is-invalid
+  (is-not (luhn:valid? "0")))
 
-(deftest create
-  (is-equal "2323 2005 7766 3554" (luhn:create "2323 2005 7766 355")))
+(deftest a-simple-valid-SIN-that-remains-valid-reversed
+  (is (luhn:valid? "059")))
+
+(deftest a-simple-valid-SIN-that-becomes-invalid-if-reversed
+  (is (luhn:valid? "59")))
+
+(deftest a-valid-Canadian-SIN
+  (is (luhn:valid? "055 444 285")))
+
+(deftest invalid-Canadian-SIN
+  (is-not (luhn:valid? "055 444 286")))
+
+(deftest invalid-credit-card
+  (is-not (luhn:valid? "8273 1232 7352 0569")))
+
+(deftest invalid-long-number-with-an-even-remainder
+  (is-not (luhn:valid? "1 2345 6789 1234 5678 9012")))
+
+(deftest invalid-long-with-a-remainder-divisible-by-5
+  (is-not (luhn:valid? "1 2345 6789 1234 5678 9013")))
+
+(deftest valid-number-with-an-even-number-of-digits
+  (is (luhn:valid? "095 245 88")))
+
+(deftest valid-number-with-an-odd-number-of-spaces
+  (is (luhn:valid? "234 567 891 234")))
+
+(deftest valid-strings-with-a-non-digit-added-at-the-end-become-invalid
+  (is-not (luhn:valid? "059a")))
+
+(deftest valid-strings-with-punctuation-included-become-invalid
+  (is-not (luhn:valid? "055-444-285")))
+
+(deftest valid-strings-with-symbols-included-become-invalid
+  (is-not (luhn:valid? "055# 444$ 285")))
+
+(deftest single-zero-with-space-is-invalid
+  (is-not (luhn:valid? " 0")))
+
+(deftest more-than-a-single-zero-is-valid
+  (is (luhn:valid? "0000 0")))
+
+(deftest input-digit-9-is-correctly-converted-to-output-digit-9
+  (is (luhn:valid? "091")))
+
+(deftest very-long-input-is-valid
+  (is (luhn:valid? "9999999999 9999999999 9999999999 9999999999")))
+
+(deftest valid-luhn-with-an-odd-number-of-digits-and-non-zero-first-digit
+  (is (luhn:valid? "109")))
+
+(deftest using-ascii-value-for-non-doubled-non-digit-isnt-allowed
+  (is-not (luhn:valid? "055b 444 285")))
+
+(deftest using-ascii-value-for-doubled-non-digit-isnt-allowed
+  (is-not (luhn:valid? ":9")))
+
+(deftest non-numeric-non-space-char-in-the-middle-with-a-sum-thats-divisible-by-10-isnt-allowed
+  (is-not (luhn:valid? "59%59")))