script.js

// Unit system state
let currentSystem = 'metric';

// Unit toggle functionality
document.querySelectorAll('.unit-btn').forEach(btn => {
    btn.addEventListener('click', function() {
        // Update active state
        document.querySelectorAll('.unit-btn').forEach(b => b.classList.remove('active'));
        this.classList.add('active');
        
        // Update current system
        currentSystem = this.dataset.system;
        
        // Toggle input visibility
        if (currentSystem === 'metric') {
            document.querySelector('.metric-input').style.display = 'block';
            document.querySelector('.imperial-input').style.display = 'none';
            document.getElementById('weight-unit').textContent = 'kg';
        } else {
            document.querySelector('.metric-input').style.display = 'none';
            document.querySelector('.imperial-input').style.display = 'block';
            document.getElementById('weight-unit').textContent = 'lbs';
        }
        
        // Clear error message
        hideError();
    });
});

// Calculate BMI
function calculateBMI() {
    hideError();
    
    // Get weight
    const weight = parseFloat(document.getElementById('weight').value);
    
    if (!weight || weight <= 0) {
        showError('Please enter a valid weight');
        return;
    }
    
    let heightInMeters;
    
    if (currentSystem === 'metric') {
        // Get height in cm
        const heightCm = parseFloat(document.getElementById('height-cm').value);
        
        if (!heightCm || heightCm <= 0) {
            showError('Please enter a valid height');
            return;
        }
        
        // Convert cm to meters
        heightInMeters = heightCm / 100;
    } else {
        // Get height in feet and inches
        const heightFt = parseFloat(document.getElementById('height-ft').value) || 0;
        const heightIn = parseFloat(document.getElementById('height-in').value) || 0;
        
        if (heightFt <= 0 && heightIn <= 0) {
            showError('Please enter a valid height');
            return;
        }
        
        // Convert feet and inches to meters
        const totalInches = (heightFt * 12) + heightIn;
        heightInMeters = totalInches * 0.0254;
    }
    
    // Calculate BMI
    let bmi;
    if (currentSystem === 'metric') {
        bmi = weight / (heightInMeters * heightInMeters);
    } else {
        // For imperial: BMI = (weight in lbs * 703) / (height in inches)^2
        const heightInInches = heightInMeters / 0.0254;
        bmi = (weight * 703) / (heightInInches * heightInInches);
    }
    
    // Display results
    displayResults(bmi, weight, heightInMeters);
}

// Display results
function displayResults(bmi, weight, heightInMeters) {
    const resultsCard = document.getElementById('results-card');
    
    // Determine category
    const category = getBMICategory(bmi);
    
    // Calculate ideal weight range
    const idealWeight = calculateIdealWeight(heightInMeters);
    
    // Get health advice
    const advice = getHealthAdvice(category.key);
    
    // Build results HTML
    const resultsHTML = `
        <div class="bmi-result">
            <div class="bmi-value">${bmi.toFixed(1)}</div>
            <div class="bmi-category category-${category.key}">${category.name}</div>
            <div class="bmi-range">${category.range}</div>
            
            <div class="bmi-details">
                <div class="detail-row">
                    <span class="detail-label">Your Weight</span>
                    <span class="detail-value">${formatWeight(weight)}</span>
                </div>
                <div class="detail-row">
                    <span class="detail-label">Your Height</span>
                    <span class="detail-value">${formatHeight(heightInMeters)}</span>
                </div>
                <div class="detail-row">
                    <span class="detail-label">Healthy BMI Range</span>
                    <span class="detail-value">18.5 - 24.9</span>
                </div>
                <div class="detail-row">
                    <span class="detail-label">Healthy Weight Range</span>
                    <span class="detail-value">${idealWeight}</span>
                </div>
            </div>
            
            <div class="health-advice ${category.key}">
                <h3>${advice.title}</h3>
                <p>${advice.message}</p>
            </div>
        </div>
    `;
    
    resultsCard.innerHTML = resultsHTML;
}

// Get BMI category
function getBMICategory(bmi) {
    if (bmi < 18.5) {
        return { key: 'underweight', name: 'Underweight', range: 'BMI less than 18.5' };
    } else if (bmi >= 18.5 && bmi < 25) {
        return { key: 'normal', name: 'Normal Weight', range: 'BMI 18.5 - 24.9' };
    } else if (bmi >= 25 && bmi < 30) {
        return { key: 'overweight', name: 'Overweight', range: 'BMI 25 - 29.9' };
    } else {
        return { key: 'obese', name: 'Obese', range: 'BMI 30 or greater' };
    }
}

// Calculate ideal weight range
function calculateIdealWeight(heightInMeters) {
    const minWeight = 18.5 * heightInMeters * heightInMeters;
    const maxWeight = 24.9 * heightInMeters * heightInMeters;
    
    if (currentSystem === 'metric') {
        return `${minWeight.toFixed(1)} - ${maxWeight.toFixed(1)} kg`;
    } else {
        const minLbs = minWeight * 2.20462;
        const maxLbs = maxWeight * 2.20462;
        return `${minLbs.toFixed(1)} - ${maxLbs.toFixed(1)} lbs`;
    }
}

// Get health advice
function getHealthAdvice(category) {
    const advice = {
        underweight: {
            title: '💡 Health Advice',
            message: 'Being underweight may indicate that you\'re not eating enough or you may be ill. If you\'re underweight, consult a doctor or dietitian for advice.'
        },
        normal: {
            title: '✅ Excellent!',
            message: 'You\'re in the healthy weight range! Maintain your weight through a balanced diet and regular physical activity.'
        },
        overweight: {
            title: '⚠️ Health Alert',
            message: 'Being overweight increases your risk of heart disease, diabetes, and other conditions. Consider adopting healthier eating habits and increasing physical activity.'
        },
        obese: {
            title: '🚨 Important Notice',
            message: 'Obesity significantly increases your risk of serious health conditions. We strongly recommend consulting a healthcare professional for personalized advice and support.'
        }
    };
    
    return advice[category];
}

// Format weight for display
function formatWeight(weight) {
    if (currentSystem === 'metric') {
        return `${weight.toFixed(1)} kg`;
    } else {
        return `${weight.toFixed(1)} lbs`;
    }
}

// Format height for display
function formatHeight(heightInMeters) {
    if (currentSystem === 'metric') {
        const heightCm = heightInMeters * 100;
        return `${heightCm.toFixed(1)} cm`;
    } else {
        const totalInches = heightInMeters / 0.0254;
        const feet = Math.floor(totalInches / 12);
        const inches = Math.round(totalInches % 12);
        return `${feet}' ${inches}"`;
    }
}

// Show error message
function showError(message) {
    const errorElement = document.getElementById('error-message');
    errorElement.textContent = message;
    errorElement.classList.add('show');
}

// Hide error message
function hideError() {
    const errorElement = document.getElementById('error-message');
    errorElement.classList.remove('show');
}

// Enter key support
document.querySelectorAll('input').forEach(input => {
    input.addEventListener('keypress', function(event) {
        if (event.key === 'Enter') {
            calculateBMI();
        }
    });
});

// Clear inputs on page load
window.addEventListener('load', function() {
    document.getElementById('weight').value = '';
    document.getElementById('height-cm').value = '';
    document.getElementById('height-ft').value = '';
    document.getElementById('height-in').value = '';
});