Synchronize Luhn exercise with canonical specs

rchavarria · rchavarria · commit 9d4abb02bafb · 2017-01-19T12:34:13.000+01:00
Canonical specs for Luhn exercise were changed, and tracks implementing that exercise should synchronize wih them. Closes #316
diff --git a/exercises/luhn/example.js b/exercises/luhn/example.js
@@ -1,63 +1,34 @@
 'use strict';
 
-function Luhn(number) {
-  this.checkDigit = number % 10;
-  this.addends = this.calculateAddends(number);
-  this.checksum = this.calculateChecksum(this.addends);
-  this.valid = this.determineIfValid(this.checksum);
-}
-
-Luhn.prototype = {
-  calculateAddends: function(number) {
-
-    var numberAsString = '' + number + '';
-    var numbers = numberAsString.split('');
-    var addends = [];
-
-    for (var i = 0; i < numbers.length; i++) {
-      var index = numbers.length - 1 - i;
-
-      var currentAddend = parseInt(numbers[index], 10);
-
-      if ((i + 1) % 2 === 0) {
-        currentAddend = currentAddend * 2;
-        if (currentAddend > 10) {
-          currentAddend = currentAddend - 9;
-        }
+function isValid(number) {
+  number = number.replace(/\s/g, '');
+  const digits = [...number];
+
+  const sum = digits
+    // convert to integers
+    .map(d => parseInt(d, 10))
+    // double even positions (odd indexes)
+    .map((d, i) => {
+      if (i % 2 !== 0) {
+        return d * 2;
       }
+      return d;
+    })
+    // limit to digits less than 10
+    .map(d => {
+      if (d > 9) {
+        return d - 9;
+      }
+      return d;
+    })
+    // sum all digits
+    .reduce((d, acc) => d + acc, 0);
 
-      addends.push(currentAddend);
-    }
-
-    return addends.reverse();
-
-  },
-  calculateChecksum: function(numbers) {
-    var sum = 0;
-    for (var i = 0; i < numbers.length; i++) {
-      sum += numbers[i];
-    }
-
-    return sum;
-  },
-  determineIfValid: function(sum) {
-    return (sum % 10 === 0);
-  }
-};
-
-Luhn.create = function(number) {
-  var finalNumber = number * 10;
-  var luhnNumber = new Luhn(finalNumber);
-  var index = 0;
-
-  while(!luhnNumber.valid) {
-    finalNumber = number * 10 + index;
-    luhnNumber = new Luhn(finalNumber);
-    if (luhnNumber.valid) { break; }
-    index += 1;
-  }
+  return sum > 0 && sum % 10 === 0;
+}
 
-  return finalNumber;
-};
+function Luhn(number) {
+  this.valid = isValid(number);
+}
 
-module.exports = Luhn;
+module.exports = Luhn;
diff --git a/exercises/luhn/luhn.spec.js b/exercises/luhn/luhn.spec.js
@@ -2,59 +2,34 @@ var Luhn = require('./luhn');
 
 describe('Luhn',function() {
 
-  it('check digit',function() {
-    var luhn = new Luhn(34567);
-    expect(luhn.checkDigit).toEqual(7);
-  });
-
-  xit('check digit again',function() {
-    var luhn = new Luhn(91370);
-    expect(luhn.checkDigit).toEqual(0);
-  });
-
-  xit('addends',function() {
-    var luhn = new Luhn(12121);
-    expect(luhn.addends).toEqual([1, 4, 1, 4, 1]);
-  });
-
-  xit('too large addend',function() {
-    var luhn = new Luhn(8631);
-    expect(luhn.addends).toEqual([7, 6, 6, 1]);
-  });
-
-  xit('checksum',function() {
-    var luhn = new Luhn(4913);
-    expect(luhn.checksum).toEqual(22);
-  });
-
-  xit('checksum again',function() {
-    var luhn = new Luhn(201773);
-    expect(luhn.checksum).toEqual(21);
+  it('single digit strings can not be valid', function () {
+    const luhn = new Luhn('1');
+    expect(luhn.valid).toEqual(false);
   });
 
-  xit('invalid number',function() {
-    var luhn = new Luhn(738);
+  xit('A single zero is invalid', function () {
+    const luhn = new Luhn('0');
     expect(luhn.valid).toEqual(false);
   });
 
-  xit('invalid number',function() {
-    var luhn = new Luhn(8739567);
+  xit('valid Canadian SIN', function () {
+    const luhn = new Luhn('046 454 286');
     expect(luhn.valid).toEqual(true);
   });
 
-  xit('create valid number',function() {
-    var number = Luhn.create(123);
-    expect(number).toEqual(1230);
+  xit('invalid Canadian SIN', function () {
+    const luhn = new Luhn('046 454 287');
+    expect(luhn.valid).toEqual(false);
   });
 
-  xit('create other valid number',function() {
-    var number = Luhn.create(873956);
-    expect(number).toEqual(8739567);
+  xit('invalid credit card', function () {
+    const luhn = new Luhn('8273 1232 7352 0569');
+    expect(luhn.valid).toEqual(false);
   });
 
-  xit('create yet another valid number',function() {
-    var number = Luhn.create(837263756);
-    expect(number).toEqual(8372637564);
+  xit('valid strings with a non-digit added become invalid', function () {
+    const luhn = new Luhn('046a 454 286');
+    expect(luhn.valid).toEqual(false);
   });
 
 });
