Add MultiTapCipherDecode.mjs

This is the code to decode the Multi Tap Cipher.
It has selection options for the user to choose the delimiter and converts numbers back to a string adhering to the MultiTap Cipher rules.
More info - https://en.wikipedia.org/wiki/Multi-tap

src/core/operations/MultiTapCipherDecode.mjs

@@ -0,0 +1,58 @@
+/**
+ * @author Necron3574 [kaustubhbm3574@gmail.com]
+ * @copyright Crown Copyright 2021
+ * @license Apache-2.0
+ */
+
+import Utils from "../Utils.mjs";
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+
+/**
+ * Multi Tap Cipher Decode operation
+ */
+class MultiTapCipherDecode extends Operation {
+
+    /**
+     * MultiTapCipherDecode constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Multi Tap Cipher Decode";
+        this.module = "Default";
+        this.description = "It is a simple substitution cipher which substitutes the alphabets to their corresponding taps on a mobile phone.<br><br>e.g. <code>adg</code> becomes <code>2-3-4</code>";
+        this.infoURL = "https://wikipedia.org/wiki/Multi-tap";
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [
+            {
+                name: "Delimiter",
+                type: "option",
+                value: ["Hyphen","Space", "Comma", "Semi-colon", "Colon", "Line feed"]
+            }
+        ];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        if(input.length == 0)
+          return "";
+        const delim = Utils.charRep(args[0] || "Hyphen");
+        var emap = {"2":"A","22":"B","222":"C","3":"D","33":"E","333":"F","4":"G","44":"H","444":"I","5":"J","55":"K","555":"L","6":"M","66":"N","666":"O","7":"P","77":"Q","777":"R","7777":"S","8":"T","88":"U","888":"V","9":"W","99":"X","999":"Y","9999":"Z"," ":" "}
+        var enc_list = input.split(delim);
+        var plaintext = "";
+        for(let i=0;i<enc_list.length;i++){
+            if(emap[enc_list[i]] == undefined)
+                throw new OperationError("Invalid Input\nThe numbers must range from 2-9 and must be separated by the delimiter chosen");
+            plaintext += emap[enc_list[i]];
+        }
+        return plaintext;
+    }
+}
+
+export default MultiTapCipherDecode;