Merge pull request #12 from Marceldts/proposal--caesar-cypher

feat: remade caesar cypher and tests

src/caesar/README.md

@@ -10,4 +10,4 @@ u = "I should have known that you would have a perfect answer for me!!!"
 
 movingShift(u, 1) returns:
 
-v = ["J vltasl rlhr ", "zdfog odxr ypw", " atasl rlhr p ", "gwkzzyq zntyhv", " lvz wp!!!"]
+v = "J ukszrk pjfp wacld kztn tkr unumf keak h xnbqqph pdjoxl ako kd!!!"

src/caesar/solutions/caesar-cypher.spec.ts

@@ -1,28 +1,33 @@
 import { describe, it, expect } from 'vitest'
 import { cypher } from './caesar-cypher'
 
-describe('cypher', () => {
-  it('should shift by one position', () => {
-    const given = 'abc'
-
-    const actual = cypher(given, 1)
-
-    expect(actual).toBe('bdf')
+describe('caesarCypher', () => {
+  it('should return an empty string when given an empty string', () => {
+    expect(cypher('', 1)).toBe('')
+  })
+  it('should shift the letters of the alphabet by the given number', () => {
+    expect(cypher('abcd', 1)).toBe('bdfh')
   })
 
-  it('should shift by two positions initially', () => {
-    const given = 'abc'
-
-    const actual = cypher(given, 2)
+  it('should ignore the blank spaces to increase the shift', () => {
+    expect(cypher('a b c d', 1)).toBe('b d f h')
+  })
 
-    expect(actual).toBe('ceg')
+  it('should work with negative shifts', () => {
+    expect(cypher('abcd', -1)).toBe('zbdf')
   })
 
-  it('should handle overflow of the alphabet', () => {
-    const given = 'xyz'
+  it('should work with large shifts', () => {
+    expect(cypher('abcd', 27)).toBe('bdfh')
+  })
 
-    const actual = cypher(given, 1)
+  it('should work with large negative shifts', () => {
+    expect(cypher('abcd', -27)).toBe('zbdf')
+  })
 
-    expect(actual).toBe('yac')
+  it('should work with the example from the README', () => {
+    expect(cypher('I should have known that you would have a perfect answer for me!!!', 1)).toBe(
+      'J ukszrk pjfp wacld kztn tkr unumf keak h xnbqqph pdjoxl ako kd!!!'
+    )
   })
 })

src/caesar/solutions/caesar-cypher.ts

@@ -1,12 +1,26 @@
-export function cypher(message: string, shiftedBy: number): string {
-  const alphabet = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz'
-  let cypheredMessage = ''
+const _ALPHABET = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz'
+const _HIGH_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ'
 
-  for (let i = 0; i < message.length; i++) {
-    const index = alphabet.indexOf(message[i]) + i + shiftedBy
-    const nextLetter = alphabet[index]
-    cypheredMessage += nextLetter
+export const cypher = (str: string, shift: number): string => {
+  if (str.length === 0) return ''
+  let decypheredString = ''
+  for (const char of str) {
+    const index: number = _ALPHABET.indexOf(char)
+    const upperIndex: number = _HIGH_ALPHABET.indexOf(char)
+    if (index !== -1 || upperIndex !== -1) {
+      const isLowerCase: boolean = index !== -1
+      const auxIndex = isLowerCase ? index : upperIndex
+      let currentIndex = auxIndex + shift
+      while (currentIndex < 0) {
+        currentIndex += 26
+      }
+      decypheredString += isLowerCase
+        ? _ALPHABET[currentIndex % 26]
+        : _HIGH_ALPHABET[currentIndex % 26]
+      shift++
+    } else {
+      decypheredString += char
+    }
   }
-
-  return cypheredMessage
+  return decypheredString
 }