Vigenere final

Reviewed-on: #1

src/vigenere_cipher_helper.py

@@ -0,0 +1,56 @@
+class VigenereCipher(object):
+    def __init__(self, key, alphabet):
+        self.key = key
+        self.alphabet = alphabet
+
+    def encode(self, text):
+        len_text = len(text)
+        len_key = len(self.key)
+
+        if len_key < len_text:
+            new_key = (
+                self.key * (len_text // len_key) + self.key[: (len_text % len_key)]
+            )
+        else:
+            new_key = self.key[:len_text]
+
+        new_text = []
+
+        for l_text, l_key in zip(text, new_key):
+            if l_text in self.alphabet:
+                if l_key in self.alphabet:
+                    new_pos = (
+                        self.alphabet.index(l_text) + self.alphabet.index(l_key)
+                    ) % len(self.alphabet)
+                else:
+                    new_pos = self.alphabet.index(l_text)
+                new_text.append(self.alphabet[new_pos])
+            else:
+                new_text.append(l_text)
+        return "".join(new_text)
+
+    def decode(self, text):
+        len_text = len(text)
+        len_key = len(self.key)
+
+        if len_key < len_text:
+            new_key = (
+                self.key * (len_text // len_key) + self.key[: (len_text % len_key)]
+            )
+        else:
+            new_key = self.key[:len_text]
+
+        new_text = []
+
+        for l_text, l_key in zip(text, new_key):
+            if l_text in self.alphabet:
+                if l_key in self.alphabet:
+                    new_pos = (
+                        self.alphabet.index(l_text) - self.alphabet.index(l_key)
+                    ) % len(self.alphabet)
+                else:
+                    new_pos = self.alphabet.index(l_text)
+                new_text.append(self.alphabet[new_pos])
+            else:
+                new_text.append(l_text)
+        return "".join(new_text)