/**

* @function caesarsCipher

* @description - In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

* @see - [wiki](https://en.wikipedia.org/wiki/Caesar_cipher)

* @param {string} str - string to be encrypted

* @param {number} rotation - the number of rotation, expect real number ( > 0)

* @return {string} - decrypted string

*/

const caesarCipher = (str, rotation) => {

if (typeof str !== 'string' || !Number.isInteger(rotation) || rotation < 0) {

throw new TypeError('Arguments are invalid')

}

const alphabets = new Array(26)

.fill()

.map((_, index) => String.fromCharCode(97 + index)) // generate all lower alphabets array a-z

const cipherMap = alphabets.reduce(

(map, char, index) => map.set(char, alphabets[(rotation + index) % 26]),

new Map()

)

return str.replace(/[a-z]/gi, (char) => {

if (/[A-Z]/.test(char)) {

return cipherMap.get(char.toLowerCase()).toUpperCase()

}

return cipherMap.get(char)

})

}

export default caesarCipher