caesar cipher

Author: dmitrymorozoff

README.md

@@ -26,5 +26,8 @@
 1. [Хеш-таблица / Hash-Table](https://github.com/dmitrymorozoff/algorithms-in-javascript/blob/master/source/hash-table/hash-table.js) | [Инфо](https://bitsofmind.wordpress.com/2008/07/28/introduction_in_hash_tables/)
 2. [Хеш-таблица c открытой адресацией / Linear hashing](https://github.com/dmitrymorozoff/algorithms-in-javascript/blob/master/source/hash-table/linear-hashing/linear-hashing.js) | [Инфо](http://algolist.manual.ru/ds/s_has.php)
 
+## Шифрование / Cryptographic
+1. [Шифр Цезаря / Caesar Cipher](https://github.com/dmitrymorozoff/algorithms-in-javascript/blob/master/source/cryptographic/caesar-cipher/caesar-cipher.js) | [Инфо](https://ru.wikipedia.org/wiki/%D0%A8%D0%B8%D1%84%D1%80_%D0%A6%D0%B5%D0%B7%D0%B0%D1%80%D1%8F)
+
 ## Другое / Other
 1. [Решето Эратосфена / Sieve Of Eratosthenes](https://github.com/dmitrymorozoff/algorithms-in-javascript/blob/master/source/other/sieve-of-eratosthenes.js) | [Инфо](https://ru.wikipedia.org/wiki/%D0%A0%D0%B5%D1%88%D0%B5%D1%82%D0%BE_%D0%AD%D1%80%D0%B0%D1%82%D0%BE%D1%81%D1%84%D0%B5%D0%BD%D0%B0)

index.html

@@ -20,6 +20,7 @@
     <script src="./source/search/linear-search/linear-search.js" type="module"></script>
     <script src="./source/search/binary-search/binary-search.js" type="module"></script>
     <script src="./source/hash-table/hash-table.js" type="module"></script>
+    <script src="./source/cryptographic/caesar-cipher/caesar-cipher.js" type="module"></script>
     <script src="./source/hash-table/linear-hashing/linear-hashing.js" type="module"></script>
     <script src="./source/other/sieve-of-eratosthenes.js" type="module"></script>
     <script src="./source/main.js" type="module"></script>

source/cryptographic/caesar-cipher/caesar-cipher.js

@@ -0,0 +1,34 @@
+export default class CaesarCipher {
+    constructor(alphabet, characters, shift) {
+        this.alphabet = alphabet.toLowerCase();
+        this.characters = characters;
+        this.shift = shift;
+        this._shiftedAlphabet = "";
+    }
+    _shiftAlhabet() {
+        this._shiftedAlphabet = this.alphabet.slice(this.shift);
+        this._shiftedAlphabet += this.alphabet.slice(0, this.shift);
+        this._shiftedAlphabet += this.characters;
+        this.alphabet += this.characters;
+    }
+    encrypt(message) {
+        let encryptMessage = "";
+        this._shiftAlhabet();
+        for (let i = 0; i < message.length; i++) {
+            let letterPositionInAlphabet = this.alphabet.indexOf(message[i]);
+            encryptMessage += this._shiftedAlphabet[letterPositionInAlphabet];
+        }
+        return encryptMessage;
+    }
+    decrypt(message) {
+        let decryptMessage = "";
+        this._shiftAlhabet();
+        for (let i = 0; i < message.length; i++) {
+            let letterPositionInAlphabet = this._shiftedAlphabet.indexOf(
+                message[i]
+            );
+            decryptMessage += this.alphabet[letterPositionInAlphabet];
+        }
+        return decryptMessage;
+    }
+}

source/cryptographic/caesar-cipher/caesar-cipher.spec.js

@@ -0,0 +1,15 @@
+import CaesarCipher from "./caesar-cipher";
+describe("caesar-cipher", () => {
+    test("should return khoor zruog after encrypt", () => {
+        const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        const characters = "/*  ";
+        const c = new CaesarCipher(alphabet, characters, 3);
+        expect(c.encrypt("hello world")).toBe("khoor zruog");
+    });
+    test("should return hello world after decrypt", () => {
+        const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        const characters = "/*  ";
+        const c = new CaesarCipher(alphabet, characters, 3);
+        expect(c.decrypt("khoor zruog")).toBe("hello world");
+    });
+});