// Package caesar is the shift cipher

// ref: https://en.wikipedia.org/wiki/Caesar_cipher

package caesar

// Encrypt encrypts by right shift of "key" each character of "input"

func Encrypt(input string, key int) string {

// if key is negative value,

// updates "key" the number which congruents to "key" modulo 26

key = (key%26 + 26) % 26

outputBuffer := []byte{}

for _, r := range input {

newByte := byte(r)

if 'A' <= newByte && newByte <= 'Z' {

outputBuffer = append(outputBuffer, byte(int('A')+int(int(newByte-'A')+key)%26))

} else if 'a' <= newByte && newByte <= 'z' {

outputBuffer = append(outputBuffer, byte(int('a')+int(int(newByte-'a')+key)%26))

} else {

outputBuffer = append(outputBuffer, newByte)

}

}

return string(outputBuffer)

}

// Decrypt decrypts by left shift of "key" each character of "input"

func Decrypt(input string, key int) string {

// left shift of "key" is same as right shift of 26-"key"

return Encrypt(input, 26-key)

}