<div class="vastenavend-calculator">
    <h3>Bereken Vastenavend</h3>

    <p>
        <label><strong>Jaar:</strong></label>
        <input type="number" id="year" min="1900" max="2200" />
        <button type="button" onclick="calcCarnival()">Reken datum uit</button>
    </p>

    <p>
        <label><strong>Neuzebal:</strong></label>
        <input type="text" id="neuzebal" readonly>
    </p>

    <p>
        <label><strong>Vastenavend:</strong></label>
        <input type="text" id="result" readonly>
    </p>

    <p>
        <label><strong>Aswoensdag:</strong></label>
        <input type="text" id="aswoensdag" readonly>
    </p>
</div>

<script>
function daysOfFebruary(year) {
    return ((year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0)) ? 29 : 28;
}

function calcCarnival() {

    const year = parseInt(document.getElementById('year').value);

    if (isNaN(year) || year < 1900 || year > 2200) {
        alert('Geen geldig jaartal. Geef een datum tussen 1900 en 2200.');
        return;
    }

    let a = year % 19;
    let b = year % 4;
    let c = year % 7;

    const M = 24;
    const N = 5;

    let d = (19 * a + M) % 30;
    let e = (2 * b + 4 * c + 6 * d + N) % 7;

    let easterMonth, easterDay;

    if ((22 + d + e) <= 31) {
        easterMonth = 3;
        easterDay = 22 + d + e;
    } else {
        easterMonth = 4;
        easterDay = d + e - 9;
    }

    let todo = 47;
    let endMonth = easterMonth;

    todo -= (easterDay - 1);

    let endDay;

    if (endMonth === 4) {
        if (todo > 31) {
            endDay = (32 + daysOfFebruary(year)) - todo;
            endMonth -= 2;
        } else {
            endDay = 32 - todo;
            endMonth -= 1;
        }
    } else {
        endDay = (daysOfFebruary(year) + 1) - todo;
        endMonth -= 1;
    }

    let beginMonth = endMonth;
    let beginDay = endDay - 3;

    if (beginDay < 1) {
        beginMonth--;
        beginDay = daysOfFebruary(year) - beginDay;
    }

    const neuzebalDate = new Date(year, beginMonth - 1, beginDay);
    neuzebalDate.setDate(neuzebalDate.getDate() - 21);

    document.getElementById('neuzebal').value =
        neuzebalDate.getDate() + '-' +
        (neuzebalDate.getMonth() + 1) + '-' +
        year;

    document.getElementById('result').value =
        beginDay + '-' + beginMonth + '-' + year +
        ' t/m ' +
        endDay + '-' + endMonth + '-' + year;

    let aswoensdagDay = endDay + 1;
    let aswoensdagMonth = endMonth;

    let daysInMonth;

    if (aswoensdagMonth === 2) {
        daysInMonth = daysOfFebruary(year);
    } else if ([4, 6, 9, 11].includes(aswoensdagMonth)) {
        daysInMonth = 30;
    } else {
        daysInMonth = 31;
    }

    if (aswoensdagDay > daysInMonth) {
        aswoensdagDay = 1;
        aswoensdagMonth++;
    }

    document.getElementById('aswoensdag').value =
        aswoensdagDay + '-' +
        aswoensdagMonth + '-' +
        year;
}
</script>

<style>
.vastenavend-calculator {
    max-width: 500px;
    margin: 20px auto;
    padding: 20px;
    border: 1px solid #ddd;
    border-radius: 8px;
}

.vastenavend-calculator input {
    padding: 6px;
    margin-left: 10px;
    width: 180px;
}

.vastenavend-calculator button {
    padding: 8px 12px;
    cursor: pointer;
}
</style>