My solution to this week’s Hunt a Killer “Mystery Mondays” cipher.

hak-mystery-mondays-2021-02-15.js

// https://www.facebook.com/groups/huntakiller/permalink/2867593840175865/

function decode( encodedPhrase = '' ) {
  
	let key = [
		[ 'A', 'B', 'C', 'D', 'E' ],
		[ 'F', 'G', 'H', 'IJ', 'K' ],
		[ 'L', 'M', 'N', 'O', 'P' ],
		[ 'Q', 'R', 'S', 'T', 'U' ],
		[ 'V', 'W', 'X', 'Y', 'Z' ]
	];

	let encodedWords = encodedPhrase.split( '  /  ' );
	let decodedWords = [];

	for (let w = 0; w < encodedWords.length; w++) {

		let encodedLetters = encodedWords[ w ].split('  ');
		let decodedLetters = [];

		for (let l = 0; l < encodedLetters.length; l++) {

			let encodedPair   = encodedLetters[ l ].split(' ');
			
			let x = encodedPair[0].length;
			let y = encodedPair[1].length;

			let decodedLetter = key[ x - 1 ][ y - 1 ];

			decodedLetters.push( decodedLetter );

		}

		let decodedWord = decodedLetters.join( '' );

		decodedWords.push( decodedWord );

	}

	let decodedPhrase = decodedWords.join( ' ' );

	return decodedPhrase;
	
}

function encode( decodedPhrase = '' ) {

	let key = [ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' ];

	// Sanitize.
	decodedPhrase = decodedPhrase.replace( /[^A-Za-z\s]+/g, '' )
	.replace( /\s+/g, ' ' )
	.toUpperCase()
	.replace( 'J', 'I' );

	let decodedWords = decodedPhrase.split(' ');
	let encodedWords = [];

	for (let w = 0; w < decodedWords.length; w++) {

		let decodedLetters = decodedWords[w].split('');
		let encodedLetters = [];

		for (let l = 0; l < decodedLetters.length; l++) {

			let decodedLetter = decodedLetters[l];

			let i = key.indexOf( decodedLetter );
			let x = Math.floor( ( i / 5 ) + 1 );
			let y = ( i % 5 ) + 1;

			let xDots = '';
			for (let ix = 0; ix < x; ix++) {
				xDots += '.';
			}

			let yDots = '';
			for (let iy = 0; iy < y; iy++) {
				yDots += '.';
			}

			let encodedLetter = [ xDots, yDots ].join(' ');

			encodedLetters.push( encodedLetter );

		}

		encodedWords.push( encodedLetters.join('  ') );
		
	}

	let encodedPhrase = encodedWords.join( '  /  ' );

	return encodedPhrase;

}

var encodedPhrase = '.. ...  .... .....  ... ...  .... ....  /  . .  /  . ...  .. ....  ... .  ... .  . .....  .... ..';
var decodedPhrase = decode( encodedPhrase ); // HUNT A CIJLLER