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    <title>AstroCalc Pro - Durasi & Waktu Matahari</title>
    
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    <style>
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        .app-header {
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        .app-header__title {
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            gap: 10px;
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        .app-header__subtitle {
            font-size: 0.85rem;
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        /* Layout Grid untuk Form */
        .form-grid {
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        .form-group {
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        .form-group--full {
            grid-column: span 2;
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        .form-label {
            font-size: 0.8rem;
            font-weight: 600;
            color: var(--color-text-main);
            margin-bottom: 6px;
            text-transform: uppercase;
            letter-spacing: 0.5px;
        }

        .form-input-wrapper {
            position: relative;
        }

        .form-input-wrapper i {
            position: absolute;
            left: 14px;
            top: 50%;
            transform: translateY(-50%);
            color: var(--color-text-muted);
            font-size: 1rem;
        }

        .form-input {
            width: 100%;
            padding: 12px 12px 12px 40px;
            background: var(--color-white);
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            font-size: 0.95rem;
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            transition: var(--transition-smooth);
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        .form-input:focus {
            border-color: var(--color-primary);
            box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.15);
        }

        /* Tombol Utama */
        .btn {
            width: 100%;
            padding: 14px;
            border: none;
            border-radius: var(--radius-md);
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: var(--transition-smooth);
            display: flex;
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            align-items: center;
            gap: 8px;
            grid-column: span 2;
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        .btn--primary {
            background: var(--color-primary);
            color: var(--color-white);
            box-shadow: 0 4px 12px rgba(79, 70, 229, 0.2);
            margin-top: 10px;
        }

        .btn--primary:hover {
            background: var(--color-primary-hover);
            transform: translateY(-2px);
            box-shadow: 0 6px 16px rgba(79, 70, 229, 0.3);
        }

        .btn--primary:active {
            transform: translateY(0);
        }

        /* Area Hasil Kalkulasi (Grid 2x2) */
        .results-section {
            margin-top: 25px;
            display: none;
            flex-direction: column;
            gap: 15px;
            animation: fadeIn 0.5s ease forwards;
        }

        .results-section.show {
            display: flex;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(15px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .result-row {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 15px;
        }

        .result-card {
            background: var(--color-white);
            padding: 18px 15px;
            border-radius: var(--radius-md);
            border: 1px solid rgba(226, 232, 240, 0.8);
            text-align: center;
            box-shadow: 0 2px 10px rgba(0,0,0,0.03);
            transition: var(--transition-smooth);
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
        }
        
        .result-card:hover {
            border-color: var(--color-primary);
            transform: translateY(-3px);
            box-shadow: 0 8px 20px rgba(0,0,0,0.06);
        }

        .result-icon {
            font-size: 1.8rem;
            margin-bottom: 10px;
        }
        
        /* Palet Warna Ikon Kartu */
        .icon-sunrise { color: #f59e0b; }
        .icon-sunset { color: #ef4444; }
        .icon-day { color: #0ea5e9; }
        .icon-night { color: #6366f1; }

        .result-label {
            font-size: 0.75rem;
            color: var(--color-text-muted);
            font-weight: 600;
            text-transform: uppercase;
            letter-spacing: 0.5px;
        }

        .result-value {
            font-size: 1.25rem;
            font-weight: 700;
            color: var(--color-text-main);
            margin-top: 4px;
        }

        /* Toast Notifikasi Kustom */
        .toast {
            position: fixed;
            bottom: 20px;
            right: 20px;
            background: var(--color-white);
            padding: 15px 20px;
            border-radius: var(--radius-md);
            box-shadow: 0 10px 25px rgba(0,0,0,0.15);
            display: flex;
            align-items: center;
            gap: 12px;
            font-weight: 500;
            font-size: 0.9rem;
            transform: translateY(150%);
            transition: transform 0.4s cubic-bezier(0.68, -0.55, 0.265, 1.55);
            z-index: 1000;
            border-left: 4px solid #ef4444;
        }

        .toast.show { transform: translateY(0); }
        .toast i { color: #ef4444; font-size: 1.2rem; }

        /* Responsivitas untuk Mobile */
        @media (max-width: 480px) {
            .app-container { padding: 25px 20px; }
            .form-grid { grid-template-columns: 1fr; gap: 12px; }
            .form-group, .form-group--full, .btn { grid-column: span 1; }
            /* Ubah Grid Hasil menjadi 1 kolom di layar sempit */
            .result-row { grid-template-columns: 1fr; gap: 12px; }
        }
    </style>
</head>
<body>

    <!-- Kontainer Aplikasi -->
    <main class="app-container">
        <header class="app-header">
            <h1 class="app-header__title"><i class="fa-solid fa-compass"></i> AstroCalc Pro</h1>
            <p class="app-header__subtitle">Presisi tinggi waktu & durasi siang-malam</p>
        </header>

        <!-- Form Input -->
        <section class="calculator-form">
            <div class="form-grid">
                <!-- Baris 1: Tanggal -->
                <div class="form-group form-group--full">
                    <label class="form-label" for="inputDate">Tanggal Pengamatan</label>
                    <div class="form-input-wrapper">
                        <i class="fa-regular fa-calendar"></i>
                        <input type="date" id="inputDate" class="form-input" required>
                    </div>
                </div>

                <!-- Baris 2: Lintang & Bujur -->
                <div class="form-group">
                    <label class="form-label" for="inputLat">Lintang (Lat)</label>
                    <div class="form-input-wrapper">
                        <i class="fa-solid fa-arrows-up-down"></i>
                        <input type="number" id="inputLat" class="form-input" placeholder="-7.0" step="any" required>
                    </div>
                </div>
                
                <div class="form-group">
                    <label class="form-label" for="inputLon">Bujur (Lon)</label>
                    <div class="form-input-wrapper">
                        <i class="fa-solid fa-arrows-left-right"></i>
                        <input type="number" id="inputLon" class="form-input" placeholder="110.4" step="any" required>
                    </div>
                </div>

                <!-- Baris 3: Timezone -->
                <div class="form-group form-group--full">
                    <label class="form-label" for="inputTz">Zona Waktu (GMT/UTC +)</label>
                    <div class="form-input-wrapper">
                        <i class="fa-regular fa-clock"></i>
                        <input type="number" id="inputTz" class="form-input" value="7" placeholder="7 untuk WIB" required>
                    </div>
                </div>

                <button type="button" id="btnCalculate" class="btn btn--primary">
                    <i class="fa-solid fa-bolt"></i> Analisis Data
                </button>
            </div>
        </section>

        <!-- Area Hasil (4 Kartu) -->
        <section id="resultsArea" class="results-section">
            <div class="result-row">
                <!-- Kartu Terbit -->
                <div class="result-card">
                    <i class="fa-solid fa-sun result-icon icon-sunrise"></i>
                    <div class="result-label">Matahari Terbit</div>
                    <div class="result-value" id="valSunrise">00:00</div>
                </div>
                <!-- Kartu Terbenam -->
                <div class="result-card">
                    <i class="fa-regular fa-sun result-icon icon-sunset"></i>
                    <div class="result-label">Matahari Terbenam</div>
                    <div class="result-value" id="valSunset">00:00</div>
                </div>
            </div>
            
            <div class="result-row">
                <!-- Kartu Durasi Siang -->
                <div class="result-card">
                    <i class="fa-solid fa-cloud-sun result-icon icon-day"></i>
                    <div class="result-label">Durasi Siang</div>
                    <div class="result-value" id="valDurationDay">0 Jam 0 Menit</div>
                </div>
                <!-- Kartu Durasi Malam -->
                <div class="result-card">
                    <i class="fa-solid fa-moon result-icon icon-night"></i>
                    <div class="result-label">Durasi Malam</div>
                    <div class="result-value" id="valDurationNight">0 Jam 0 Menit</div>
                </div>
            </div>
        </section>
    </main>

    <!-- Toast Modal -->
    <div id="toastMessage" class="toast">
        <i class="fa-solid fa-circle-exclamation"></i>
        <span id="toastText">Pesan error di sini</span>
    </div>

    <!-- Logika JavaScript -->
    <script>
        document.addEventListener('DOMContentLoaded', () => {
            // Referensi DOM
            const inputDate = document.getElementById('inputDate');
            const inputLat = document.getElementById('inputLat');
            const inputLon = document.getElementById('inputLon');
            const inputTz = document.getElementById('inputTz');
            const btnCalculate = document.getElementById('btnCalculate');
            const resultsArea = document.getElementById('resultsArea');
            
            const valSunrise = document.getElementById('valSunrise');
            const valSunset = document.getElementById('valSunset');
            const valDurationDay = document.getElementById('valDurationDay');
            const valDurationNight = document.getElementById('valDurationNight');

            // Default: Hari ini
            inputDate.valueAsDate = new Date();

            // Fungsi Notifikasi Modern
            const showToast = (message) => {
                const toast = document.getElementById('toastMessage');
                document.getElementById('toastText').textContent = message;
                
                toast.classList.add('show');
                
                // Hilangkan setelah 3 detik
                setTimeout(() => {
                    toast.classList.remove('show');
                }, 3000);
            };

            /**
             * Mesin Algoritma Astronomi (Trigonometri Bola)
             * Menghasilkan waktu terbit, terbenam, durasi siang, dan malam.
             */
            const calculateSolarTimes = (lat, lon, tz, dateStr) => {
                const date = new Date(dateStr);
                const rad = Math.PI / 180;
                const deg = 180 / Math.PI;

                // Julian Date
                const jd = (date.getTime() / 86400000) - (date.getTimezoneOffset() / 1440) + 2440587.5;
                const d = jd - 2451545.0; 

                // Anomali & Ecliptic
                const g = (357.529 + 0.98560028 * d) % 360;
                const q = (280.459 + 0.98564736 * d) % 360;
                const L = (q + 1.915 * Math.sin(g * rad) + 0.020 * Math.sin(2 * g * rad)) % 360;

                const e = 23.439 - 0.00000036 * d;
                const decRad = Math.asin(Math.sin(e * rad) * Math.sin(L * rad));
                
                // Equation of Time
                let ra = Math.atan2(Math.cos(e * rad) * Math.sin(L * rad), Math.cos(L * rad)) * deg;
                ra = ra < 0 ? ra + 360 : ra;
                const eqt = (q / 15) - (ra / 15); // Jam

                // Hour Angle (t)
                const hRad = -0.8333 * rad; // Koreksi ufuk (refraksi + diameter matahari)
                const latRad = lat * rad;
                
                const cosT = (Math.sin(hRad) - Math.sin(latRad) * Math.sin(decRad)) / (Math.cos(latRad) * Math.cos(decRad));

                // Kondisi Polar (Matahari tidak terbit / tidak terbenam)
                if (cosT > 1) return { error: "Malam 24 Jam (Polar Night)" };
                if (cosT < -1) return { error: "Siang 24 Jam (Midnight Sun)" };

                const tDeg = Math.acos(cosT) * deg;
                const tHour = tDeg / 15; 

                // Perhitungan Final
                const transit = 12 + tz - (lon / 15) - eqt;
                const sunrise = transit - tHour;
                const sunset = transit + tHour;
                const durationDay = tHour * 2;
                const durationNight = 24 - durationDay; // Sisa dari 24 jam

                return { sunrise, sunset, durationDay, durationNight };
            };

            // Helper: Format ke HH:MM
            const formatHourTime = (decimalHours) => {
                let h = (decimalHours + 24) % 24;
                let hrs = Math.floor(h);
                let mins = Math.round((h - hrs) * 60);
                
                if (mins === 60) { hrs += 1; mins = 0; }
                if (hrs === 24) hrs = 0;

                return `${String(hrs).padStart(2, '0')}:${String(mins).padStart(2, '0')}`;
            };

            // Helper: Format ke "X Jam Y Menit"
            const formatDuration = (decimalHours) => {
                let hrs = Math.floor(decimalHours);
                let mins = Math.round((decimalHours - hrs) * 60);
                if (mins === 60) { hrs += 1; mins = 0; }
                return `${hrs} Jam ${mins} Menit`;
            };

            // Eksekutor Klik Tombol
            btnCalculate.addEventListener('click', () => {
                const lat = parseFloat(inputLat.value);
                const lon = parseFloat(inputLon.value);
                const tz = parseFloat(inputTz.value);
                const date = inputDate.value;

                // Validasi Basic
                if (!date || isNaN(lat) || isNaN(lon) || isNaN(tz)) {
                    showToast('Harap isi semua kolom dengan data yang valid.');
                    return;
                }
                if (lat < -90 || lat > 90) {
                    showToast('Garis Lintang (Lat) harus antara -90 dan 90.');
                    return;
                }
                if (lon < -180 || lon > 180) {
                    showToast('Garis Bujur (Lon) harus antara -180 dan 180.');
                    return;
                }

                // Efek visual tombol loading
                const originalText = btnCalculate.innerHTML;
                btnCalculate.innerHTML = '<i class="fa-solid fa-spinner fa-spin"></i> Memproses...';
                
                setTimeout(() => {
                    const result = calculateSolarTimes(lat, lon, tz, date);

                    btnCalculate.innerHTML = originalText; // Kembalikan teks

                    if (result.error) {
                        showToast(result.error);
                        resultsArea.classList.remove('show');
                        return;
                    }

                    // Tampilkan Data ke UI
                    valSunrise.textContent = formatHourTime(result.sunrise);
                    valSunset.textContent = formatHourTime(result.sunset);
                    valDurationDay.textContent = formatDuration(result.durationDay);
                    valDurationNight.textContent = formatDuration(result.durationNight);

                    resultsArea.classList.add('show');
                }, 300); // Simulasi delay animasi
            });
        });
    </script>
</body>
</html>