implemented vigenere cipher and basic test

psyfer/vigenere.go

@@ -0,0 +1,29 @@
+package psyfer
+
+func VigenereCipher(input string, key string, decrypt bool) string {
+	alphabet := "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	chars := []rune(input)
+	k := []rune(key)
+	keyPos := 0
+	output := ""
+	for _, m := range chars {
+		index := int(m - 'A')
+		offset := int(k[keyPos]-'A') % 26
+		if decrypt {
+			index -= offset
+		} else {
+			index += offset
+		}
+		if index >= 26 {
+			index -= 26
+		} else if index < 0 {
+			index += 26
+		}
+		output += string(alphabet[index])
+		keyPos++
+		if keyPos == len(key) {
+			keyPos = 0
+		}
+	}
+	return output
+}

psyfer/vigenere_test.go

@@ -0,0 +1,35 @@
+package psyfer
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestVigenereCipher(t *testing.T) {
+	key := "vig"
+	input := "theboyhasthebag"
+	input = strings.ToUpper(strings.Replace(input, " ", "", -1))
+	key = strings.ToUpper(strings.Replace(key, " ", "", -1))
+	expected := "OPKWWECIYOPKWIM"
+	actual := VigenereCipher(input, key, false)
+	if expected != actual {
+		t.Errorf(
+			"failed VigenereCipher:\n\texpected: % q\n\t  actual: % q",
+			expected,
+			actual,
+		)
+	}
+	key = "vig"
+	input = "OPKWWECIYOPKWIM"
+	input = strings.ToUpper(strings.Replace(input, " ", "", -1))
+	key = strings.ToUpper(strings.Replace(key, " ", "", -1))
+	expected = "THEBOYHASTHEBAG"
+	actual = VigenereCipher(input, key, true)
+	if expected != actual {
+		t.Errorf(
+			"failed VigenereCipher:\n\texpected: % q\n\t  actual: % q",
+			expected,
+			actual,
+		)
+	}
+}