<!DOCTYPE html>
<html lang="id">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Kalkulator Luas Lingkaran</title>
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.4.0/css/all.min.css">
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }

        body {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            color: #fff;
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 20px;
        }

        .container {
            max-width: 1000px;
            width: 100%;
            background: rgba(255, 255, 255, 0.1);
            border-radius: 20px;
            padding: 40px;
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.2);
            box-shadow: 0 15px 35px rgba(0, 0, 0, 0.3);
        }

        header {
            text-align: center;
            margin-bottom: 40px;
        }

        h1 {
            font-size: 3rem;
            margin-bottom: 15px;
            color: #ffdd00;
            text-shadow: 0 0 15px rgba(255, 221, 0, 0.5);
        }

        .subtitle {
            font-size: 1.3rem;
            color: #e0e0e0;
            margin-bottom: 10px;
        }

        .content {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 40px;
            align-items: center;
        }

        .calculator-section {
            background: rgba(255, 255, 255, 0.05);
            padding: 30px;
            border-radius: 15px;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .formula-box {
            background: rgba(0, 0, 0, 0.3);
            padding: 20px;
            border-radius: 10px;
            text-align: center;
            margin-bottom: 25px;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .formula {
            font-size: 2rem;
            font-weight: bold;
            color: #4ecdc4;
        }

        .pi-value {
            font-size: 1.1rem;
            color: #ffdd00;
            margin-top: 10px;
        }

        .input-group {
            margin-bottom: 20px;
        }

        .input-group label {
            display: block;
            margin-bottom: 10px;
            color: #e0e0e0;
            font-size: 1.1rem;
            font-weight: 500;
        }

        .input-group input {
            width: 100%;
            padding: 15px;
            border-radius: 10px;
            border: 2px solid rgba(255, 255, 255, 0.2);
            background: rgba(0, 0, 0, 0.3);
            color: white;
            font-size: 1.2rem;
            transition: all 0.3s ease;
        }

        .input-group input:focus {
            outline: none;
            border-color: #4ecdc4;
            box-shadow: 0 0 0 3px rgba(78, 205, 196, 0.3);
            transform: scale(1.02);
        }

        .calculate-btn {
            width: 100%;
            padding: 16px;
            background: linear-gradient(135deg, #4ecdc4, #45b7d1);
            border: none;
            border-radius: 10px;
            color: white;
            font-size: 1.3rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            margin-top: 10px;
        }

        .calculate-btn:hover {
            transform: translateY(-3px);
            box-shadow: 0 8px 20px rgba(78, 205, 196, 0.4);
            background: linear-gradient(135deg, #45b7d1, #4ecdc4);
        }

        .calculate-btn:active {
            transform: translateY(1px);
        }

        .result {
            margin-top: 25px;
            padding: 20px;
            background: rgba(78, 205, 196, 0.15);
            border-radius: 10px;
            border-left: 5px solid #4ecdc4;
            font-size: 1.4rem;
            text-align: center;
            display: none;
            animation: fadeIn 0.5s ease;
        }

        .visualization {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
        }

        .circle-container {
            position: relative;
            width: 300px;
            height: 300px;
            margin: 20px 0;
        }

        .circle {
            width: 100%;
            height: 100%;
            background: conic-gradient(
                #4ecdc4 0% 25%,
                #45b7d1 25% 50%,
                #36b1a0 50% 75%,
                #2d9585 75% 100%
            );
            border-radius: 50%;
            border: 4px solid white;
            box-shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
            transition: all 0.5s ease;
            position: relative;
            overflow: hidden;
        }

        .radius-line {
            position: absolute;
            top: 50%;
            left: 50%;
            width: 50%;
            height: 3px;
            background: #ffdd00;
            transform-origin: 0 0;
            transform: rotate(45deg);
            transition: all 0.5s ease;
        }

        .radius-label {
            position: absolute;
            top: 35%;
            left: 65%;
            background: rgba(0, 0, 0, 0.7);
            color: #ffdd00;
            padding: 5px 10px;
            border-radius: 5px;
            font-size: 1rem;
            font-weight: bold;
            transform: translate(-50%, -50%);
        }

        .center-point {
            position: absolute;
            top: 50%;
            left: 50%;
            width: 12px;
            height: 12px;
            background: #ff6b6b;
            border-radius: 50%;
            transform: translate(-50%, -50%);
            border: 2px solid white;
        }

        .diameter-line {
            position: absolute;
            top: 50%;
            left: 25%;
            width: 50%;
            height: 2px;
            background: #ff6b6b;
            transform: translateY(-50%);
            display: none;
        }

        .explanation {
            margin-top: 30px;
            padding: 25px;
            background: rgba(255, 255, 255, 0.05);
            border-radius: 15px;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .explanation h3 {
            color: #ffdd00;
            margin-bottom: 15px;
            font-size: 1.5rem;
        }

        .explanation p {
            line-height: 1.6;
            color: #e0e0e0;
            margin-bottom: 10px;
        }

        .properties {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 15px;
            margin-top: 20px;
        }

        .property-card {
            background: rgba(255, 255, 255, 0.05);
            padding: 15px;
            border-radius: 10px;
            text-align: center;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .examples {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 15px;
            margin-top: 20px;
        }

        .example-card {
            background: rgba(255, 255, 255, 0.05);
            padding: 15px;
            border-radius: 10px;
            text-align: center;
            border: 1px solid rgba(255, 255, 255, 0.1);
            transition: transform 0.3s ease;
            cursor: pointer;
        }

        .example-card:hover {
            transform: translateY(-5px);
            background: rgba(255, 255, 255, 0.1);
        }

        .controls {
            display: flex;
            gap: 10px;
            margin-top: 20px;
            justify-content: center;
        }

        .control-btn {
            padding: 10px 20px;
            background: rgba(255, 255, 255, 0.1);
            border: 1px solid rgba(255, 255, 255, 0.3);
            color: white;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .control-btn:hover {
            background: rgba(255, 255, 255, 0.2);
            transform: translateY(-2px);
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        @keyframes pulse {
            0% { transform: scale(1); }
            50% { transform: scale(1.05); }
            100% { transform: scale(1); }
        }

        @keyframes rotateCircle {
            from { transform: rotate(0deg); }
            to { transform: rotate(360deg); }
        }

        @media (max-width: 768px) {
            .content {
                grid-template-columns: 1fr;
            }
            
            h1 {
                font-size: 2.2rem;
            }
            
            .circle-container {
                width: 250px;
                height: 250px;
            }
            
            .examples, .properties {
                grid-template-columns: 1fr;
            }
        }
    </style>
</head>
<body>
    <div class="container">
        <header>
            <h1><i class="fas fa-circle"></i> Kalkulator Luas Lingkaran</h1>
            <p class="subtitle">Hitung luas lingkaran dengan visualisasi yang interaktif</p>
        </header>

        <div class="content">
            <div class="calculator-section">
                <div class="formula-box">
                    <div class="formula">L = π × r²</div>
                    <p style="margin-top: 10px; color: #ccc;">Luas = Pi × Jari-jari × Jari-jari</p>
                    <div class="pi-value">π ≈ 3.14159265359</div>
                </div>
                
                <div class="input-group">
                    <label for="circle-radius"><i class="fas fa-dot-circle"></i> Jari-jari (r):</label>
                    <input type="number" id="circle-radius" placeholder="Masukkan jari-jari" step="any" min="0">
                </div>
                
                <div class="input-group">
                    <label for="circle-diameter"><i class="fas fa-arrows-alt-h"></i> Diameter (d):</label>
                    <input type="number" id="circle-diameter" placeholder="Masukkan diameter" step="any" min="0">
                </div>
                
                <button class="calculate-btn" onclick="calculateCircleArea()">
                    <i class="fas fa-calculator"></i> Hitung Luas
                </button>
                
                <div class="result" id="circle-result">
                    <i class="fas fa-check-circle"></i> <span id="result-text"></span>
                </div>

                <div class="controls">
                    <button class="control-btn" onclick="toggleDiameter()">
                        <i class="fas fa-eye"></i> Tampilkan Diameter
                    </button>
                    <button class="control-btn" onclick="animateCircle()">
                        <i class="fas fa-play"></i> Animasi
                    </button>
                </div>
            </div>

            <div class="visualization">
                <h3 style="margin-bottom: 20px; color: #ffdd00;">Visualisasi Lingkaran</h3>
                <div class="circle-container">
                    <div class="circle" id="animated-circle">
                        <div class="radius-line" id="radius-line"></div>
                        <div class="radius-label" id="radius-label">r</div>
                        <div class="center-point"></div>
                        <div class="diameter-line" id="diameter-line"></div>
                    </div>
                </div>
                <p style="text-align: center; color: #e0e0e0; margin-top: 20px;">
                    Lingkaran adalah himpunan semua titik yang berjarak sama dari titik pusat
                </p>
            </div>
        </div>

        <div class="explanation">
            <h3><i class="fas fa-lightbulb"></i> Penjelasan Luas Lingkaran</h3>
            <p>Lingkaran adalah bangun datar dua dimensi yang terdiri dari semua titik yang memiliki jarak sama dari suatu titik pusat.</p>
            
            <p><strong>Rumus Luas Lingkaran:</strong> L = π × r²</p>
            
            <p><strong>Keterangan:</strong>
                <br>• L = Luas lingkaran
                <br>• π (pi) = Konstanta matematika ≈ 3.14159
                <br>• r = Jari-jari lingkaran
                <br>• d = Diameter lingkaran = 2 × r
            </p>

            <div class="properties">
                <div class="property-card">
                    <h4><i class="fas fa-ruler"></i> Jari-jari (r)</h4>
                    <p>Jarak dari pusat ke titik mana pun pada lingkaran</p>
                </div>
                <div class="property-card">
                    <h4><i class="fas fa-arrows-alt-h"></i> Diameter (d)</h4>
                    <p>Jarak terpanjang melalui pusat lingkaran (d = 2r)</p>
                </div>
                <div class="property-card">
                    <h4><i class="fas fa-circle"></i> Keliling (K)</h4>
                    <p>K = 2 × π × r</p>
                </div>
                <div class="property-card">
                    <h4><i class="fas fa-pi"></i> Nilai π</h4>
                    <p>Rasio keliling terhadap diameter</p>
                </div>
            </div>
            
            <div class="examples">
                <div class="example-card" onclick="setExample(7)">
                    <strong>Contoh 1</strong>
                    <p>r = 7 cm</p>
                    <p>L = π × 7² ≈ 153.94 cm²</p>
                </div>
                <div class="example-card" onclick="setExample(10)">
                    <strong>Contoh 2</strong>
                    <p>r = 10 m</p>
                    <p>L = π × 10² ≈ 314.16 m²</p>
                </div>
                <div class="example-card" onclick="setExample(14)">
                    <strong>Contoh 3</strong>
                    <p>r = 14 cm</p>
                    <p>L = π × 14² ≈ 615.75 cm²</p>
                </div>
            </div>
        </div>
    </div>

    <script>
        let diameterVisible = false;

        // Fungsi untuk menghitung luas lingkaran
        function calculateCircleArea() {
            let radius = parseFloat(document.getElementById('circle-radius').value);
            const diameter = parseFloat(document.getElementById('circle-diameter').value);
            const resultElement = document.getElementById('circle-result');
            const resultText = document.getElementById('result-text');
            const circle = document.getElementById('animated-circle');
            
            // Jika diameter diisi, hitung radius
            if (diameter > 0) {
                radius = diameter / 2;
                document.getElementById('circle-radius').value = radius;
            }
            
            if (isNaN(radius) || radius <= 0) {
                resultText.innerHTML = "Masukkan jari-jari atau diameter yang valid!";
                resultElement.style.display = 'block';
                resultElement.style.background = 'rgba(255, 100, 100, 0.15)';
                resultElement.style.borderLeftColor = '#ff6b6b';
                return;
            }
            
            const area = Math.PI * radius * radius;
            
            // Update hasil
            resultText.innerHTML = `Luas Lingkaran = <strong>${area.toFixed(2)}</strong> satuan²<br>
                                  <small>π = ${Math.PI.toFixed(10)}</small>`;
            resultElement.style.display = 'block';
            resultElement.style.background = 'rgba(78, 205, 196, 0.15)';
            resultElement.style.borderLeftColor = '#4ecdc4';
            
            // Update visualisasi
            updateVisualization(radius);
            
            // Animasi
            circle.style.animation = 'pulse 0.5s ease';
            setTimeout(() => {
                circle.style.animation = '';
            }, 500);
        }
        
        // Fungsi untuk memperbarui visualisasi
        function updateVisualization(radius) {
            document.getElementById('radius-label').textContent = `r = ${radius}`;
            
            const circle = document.getElementById('animated-circle');
            const scale = Math.min(150 / radius, 2); // Skala maksimal 2
            
            circle.style.transform = `scale(${scale})`;
            
            // Update diameter line jika terlihat
            if (diameterVisible) {
                document.getElementById('diameter-line').style.display = 'block';
            }
        }
        
        // Fungsi untuk toggle diameter
        function toggleDiameter() {
            diameterVisible = !diameterVisible;
            const diameterLine = document.getElementById('diameter-line');
            const button = event.target.closest('button');
            
            if (diameterVisible) {
                diameterLine.style.display = 'block';
                button.innerHTML = '<i class="fas fa-eye-slash"></i> Sembunyikan Diameter';
            } else {
                diameterLine.style.display = 'none';
                button.innerHTML = '<i class="fas fa-eye"></i> Tampilkan Diameter';
            }
        }
        
        // Fungsi untuk animasi lingkaran
        function animateCircle() {
            const circle = document.getElementById('animated-circle');
            const button = event.target.closest('button');
            
            if (circle.style.animationName === 'rotateCircle') {
                circle.style.animation = 'none';
                button.innerHTML = '<i class="fas fa-play"></i> Animasi';
            } else {
                circle.style.animation = 'rotateCircle 5s linear infinite';
                button.innerHTML = '<i class="fas fa-pause"></i> Stop';
            }
        }
        
        // Fungsi untuk mengisi contoh
        function setExample(radiusValue) {
            document.getElementById('circle-radius').value = radiusValue;
            document.getElementById('circle-diameter').value = '';
            calculateCircleArea();
        }
        
        // Event listener untuk input radius
        document.getElementById('circle-radius').addEventListener('input', function() {
            const radius = parseFloat(this.value);
            if (!isNaN(radius) && radius > 0) {
                document.getElementById('circle-diameter').value = (radius * 2).toFixed(2);
            } else {
                document.getElementById('circle-diameter').value = '';
            }
        });
        
        // Event listener untuk input diameter
        document.getElementById('circle-diameter').addEventListener('input', function() {
            const diameter = parseFloat(this.value);
            if (!isNaN(diameter) && diameter > 0) {
                document.getElementById('circle-radius').value = (diameter / 2).toFixed(2);
            } else {
                document.getElementById('circle-radius').value = '';
            }
        });
        
        // Event listener untuk Enter
        document.getElementById('circle-radius').addEventListener('keypress', function(e) {
            if (e.key === 'Enter') calculateCircleArea();
        });
        
        document.getElementById('circle-diameter').addEventListener('keypress', function(e) {
            if (e.key === 'Enter') calculateCircleArea();
        });
        
        // Animasi saat halaman dimuat
        document.addEventListener('DOMContentLoaded', function() {
            const circle = document.getElementById('animated-circle');
            circle.style.transform = 'scale(0)';
            circle.style.transition = 'transform 0.8s ease';
            
            setTimeout(() => {
                circle.style.transform = 'scale(1)';
            }, 300);
            
            // Set contoh default
            setExample(10);
        });
    </script>
</body>
</html>
