Added cipher

Author: sylvesterdas

cipher.js

@@ -0,0 +1,28 @@
+const { Transform, TransformCallback } = require('stream');
+
+class CeaserCipherTransform extends Transform {
+
+    /**
+     * @param {number} key
+     */
+    set key(key) {
+        this._key = key;
+    }
+
+    /**
+     * 
+     * @param {Buffer} chunk 
+     * @param {BufferEncoding} encoding 
+     * @param {TransformCallback} callback 
+     */
+    _transform(chunk, _, callback) {
+        this.push(cipher(chunk, this._key));
+        callback();
+    }
+}
+
+function cipher(chunk, key) {
+    return chunk.map(byte => byte + (key % 26));
+}
+
+module.exports = { CeaserCipherTransform };

index.js

@@ -0,0 +1,94 @@
+"use strict";
+
+const { CeaserCipherTransform } = require("./cipher");
+
+/**
+ * Encrypt a string using Caesar Cipher
+ * 
+ * @param {string} str
+ * @param {number} key
+ * @returns string
+ */
+function encryptString(str, key) {
+  return str
+    .split("")
+    .map((s) => s.charCodeAt(0) + (key % 26))
+    .map((v) => String.fromCharCode(v))
+    .join("");
+}
+
+/**
+ * Decrypt a string using Caesar Cipher
+ * 
+ * @param {string} str
+ * @param {number} key
+ * @returns string
+ */
+function decryptString(str, key) {
+  return str
+    .split("")
+    .map((s) => s.charCodeAt(0) - (key % 26))
+    .map((v) => String.fromCharCode(v))
+    .join("");
+}
+
+/**
+ * Encrypt a buffer array using Caesar Cipher
+ * 
+ * @param {Buffer} buffer
+ * @param {number} key
+ * @returns buffer
+ */
+function encrypt(buffer, key) {
+    return buffer
+        .map((byte) => byte + (key % 26));
+}
+
+/**
+ * Decrypt a buffer array using Caesar Cipher
+ * 
+ * @param {Buffer} buffer
+ * @param {number} key
+ * @returns buffer
+ */
+function decrypt(buffer, key) {
+    return buffer
+        .map((byte) => byte - (key % 26));
+}
+
+
+class EncryptTransform extends CeaserCipherTransform {
+
+    /**
+     * Transform stream for encryption using Caesar Cipher
+     * 
+     * @param {number} key Encryption key
+     */
+    constructor(key) {
+        super();
+        this.key = key;
+    }
+}
+
+class DecryptTransform extends CeaserCipherTransform {
+
+    /**
+     * Transform stream for decryption using Caesar Cipher
+     * 
+     * @param {number} key Decryption key
+     */
+    constructor(key) {
+        super();
+        this.key = -key;
+    }
+}
+
+module.exports = {
+    encrypt,
+    decrypt,
+    encryptString,
+    decryptString,
+    EncryptTransform,
+    DecryptTransform
+}
+