Renaming files according to naming convention (#158)

Ciphers/VigenereCipher.js

@@ -0,0 +1,78 @@
+/**
+ * Check if the Character is letter or not
+ * @param {String} str - character to check
+ * @return {object} An array with the character or null if isn't a letter
+ */
+function isLetter (str) {
+  return str.length === 1 && str.match(/[a-zA-Z]/i)
+}
+
+/**
+ * Check if is Uppercase or Lowercase
+ * @param {String} character - character to check
+ * @return {Boolean} result of the checking
+ */
+function isUpperCase (character) {
+  if (character === character.toUpperCase()) {
+    return true
+  }
+  if (character === character.toLowerCase()) {
+    return false
+  }
+}
+
+/**
+ * Encrypt a Vigenere cipher
+ * @param {String} message - string to be encrypted
+ * @param {String} key - key for encrypt
+ * @return {String} result - encrypted string
+ */
+function encrypt (message, key) {
+  let result = ''
+
+  for (let i = 0, j = 0; i < message.length; i++) {
+    const c = message.charAt(i)
+    if (isLetter(c)) {
+      if (isUpperCase(c)) {
+        result += String.fromCharCode((c.charCodeAt(0) + key.toUpperCase().charCodeAt(j) - 2 * 65) % 26 + 65) // A: 65
+      } else {
+        result += String.fromCharCode((c.charCodeAt(0) + key.toLowerCase().charCodeAt(j) - 2 * 97) % 26 + 97) // a: 97
+      }
+    } else {
+      result += c
+    }
+    j = ++j % key.length
+  }
+  return result
+}
+
+/**
+ * Decrypt a Vigenere cipher
+ * @param {String} message - string to be decrypted
+ * @param {String} key - key for decrypt
+ * @return {String} result - decrypted string
+ */
+function decrypt (message, key) {
+  let result = ''
+
+  for (let i = 0, j = 0; i < message.length; i++) {
+    const c = message.charAt(i)
+    if (isLetter(c)) {
+      if (isUpperCase(c)) {
+        result += String.fromCharCode(90 - (25 - (c.charCodeAt(0) - key.toUpperCase().charCodeAt(j))) % 26)
+      } else {
+        result += String.fromCharCode(122 - (25 - (c.charCodeAt(0) - key.toLowerCase().charCodeAt(j))) % 26)
+      }
+    } else {
+      result += c
+    }
+    j = ++j % key.length
+  }
+  return result
+}
+
+const messageEncrypt = encrypt('Hello World!', 'code')
+console.log(messageEncrypt) // "Jhpnr Yrvng!"
+
+const messageDecrypt = decrypt('Jsopq Zstzg!', 'code')
+console.log(messageDecrypt) // "Hello World!"