function getRandomItem(arr) {
    return arr[Math.floor(Math.random() * arr.length)];
}

function getRandomLetter() {
    const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    return getRandomItem(alphabet.split(''));
}

function getRandomLetterUpToL() {
    const alphabet = 'ABCDEFGHIJKL';
    return getRandomItem(alphabet.split(''));
}

function getRandomPrefixFirstLetter() {
    const letters = ['A', 'K', 'N', 'W'];
    return getRandomItem(letters);
}

function getRandomRegionNumber() {
    const numbers = '0123456789';
    return getRandomItem(numbers.split(''));
}

function generateRandomCallsignForFormat(format) {
    let prefix = '';
    let suffix = '';
    const regionNum = getRandomRegionNumber();

    switch (format) {
        case '1x3':
            const oneLetterPrefixes = ['K', 'N', 'W'];
            prefix = getRandomItem(oneLetterPrefixes);
            suffix = getRandomLetter() + getRandomLetter() + getRandomLetter();
            break;

        case '2x3':
            prefix = getTwoLetterPrefix();
            suffix = getRandomLetter() + getRandomLetter() + getRandomLetter();
            // Exclude 'X' as first letter of suffix for 2x3
            while (suffix.charAt(0) === 'X') {
                suffix = getRandomLetter() + getRandomLetter() + getRandomLetter();
            }
            break;

        case '1x2':
            // 1 letter prefix (K, N, or W), 1 number, 2 letter suffix (Extra Class only)
            const shortPrefixes = ['K', 'N', 'W'];
            prefix = getRandomItem(shortPrefixes);
            suffix = getRandomLetter() + getRandomLetter();
            break;

        case '2x1':
            prefix = getTwoLetterPrefix();
            suffix = getRandomLetter();
            break;

        case '2x2':
            prefix = getTwoLetterPrefix();
            suffix = getRandomLetter() + getRandomLetter() + getRandomLetter();
            break;

        default:
            return "ERR";
    }

    return prefix + regionNum + suffix;
}

function getTwoLetterPrefix() {
	var prefixes = ['A', 'K', 'N', 'W'];
	var prefix = getRandomItem(prefixes);
	if (prefix == 'A'){
		prefix += getRandomLetterUpToL();
	} else {
		prefix += getRandomLetter();
	}
	return prefix;
}

function generateRandomCallsign() {
    const formats = ['1x2'];
//    const formats = ['1x2', '2x1', '2x2', '1x3', '2x3'];
    var format = getRandomItem(formats);
    return generateRandomCallsignForFormat(format);
}