function solve(arr) {

    let username = arr.slice(0, 1)[0];
    let cmd = arr.slice(1);

    for (let command of cmd) {
        [cmd, paramOne, paramTwo] = command.split(' ');

        switch (cmd) {
            case 'Case':
                username = toLowerToUpper(paramOne, username);
                break;

            case 'Reverse':
                reverseUsername(+paramOne, +paramTwo, username);
                break;

            case 'Cut':
                break;
        }
    }

    function toLowerToUpper(currentCase, username) {
        if (currentCase === 'lower') {
            username = toLowerCase();
        } else {
            username = toUpperCase();
        }

        console.log(username);
        return username;

    }

    function reverseUsername(startIndex, endIndex, username) {

        if (startIndex < 0 || startIndex > username.lenght - 1 ||
            startIndex > endIndex || endIndex > username.lenght - 1) {
            return;
        }

        let substring = username.substring(startIndex, endIndex + 1).split('').reverse().join('');
        console.log(substring);

    }
}

// solve(['Pesho',
//     'Case lower',
//     'Cut ES',
//     'Check @',
//     'Sign up']);

solve(['ThisIsMyString',
    'Reverse 1 4',
    'Replace i',
    'Cut My',
    'Sign up'
]);