Rosetta Stone

function solve(input){
    let output = [];
    //CONCATTER FUNCTION
let concatter = (arr, length)=>{
    let size = arr.length;
    while(arr.length<length){
       for(let i = 0; i<size; i++){
           let current = arr[i];
           if(arr.length>=length){
               break;
           }else{
               arr.push(current);
           }
       }
    }

    return arr;
}
/////////

//
    let rosetaStone = [' '];
    for(let i = 65; i<=90; i++){
        rosetaStone.push(String.fromCharCode(i));
    }
//


let arr = input.slice(0);
let templateSize = Number(arr.shift());
let template = arr.splice(0,templateSize).map(item=>{
    return item.split(' ').map(Number);
 });

 let matrix = arr.map(item=>{
    return item.split(' ').map(Number);
});

let matrixRowSize = matrix[0].length;

let templateMatrix = template.map(item=>{
    return concatter(item,matrixRowSize);
});

    let fullTemplate = concatter(templateMatrix,matrix.length);


    for(let row = 0; row < matrix.length; row++){
        for(let col = 0; col < matrix[row].length; col++){
            let currentTemplate = fullTemplate[row][col];
            matrix[row][col] += currentTemplate;
            matrix[row][col] = matrix[row][col]%27;
            let index = matrix[row][col];
            output.push(rosetaStone[index]);
        }

    }
    return output.join('');
}