/**
 * Utilities Module
 * Contains helper functions used across the application
 */
const Utils = (() => {
    /**
     * Format a date string (YYYY-MM-DD) to a more readable format
     * @param {string} dateString - Date in YYYY-MM-DD format
     * @returns {string} - Formatted date (e.g., "May 26, 2025")
     */
    const formatDate = (dateString) => {
        if (!dateString) return '';
        const date = new Date(dateString);
        return date.toLocaleDateString('en-US', { 
            year: 'numeric', 
            month: 'long', 
            day: 'numeric' 
        });
    };

    /**
     * Get today's date in YYYY-MM-DD format
     * @returns {string} - Today's date
     */
    const getTodayDate = () => {
        const today = new Date();
        return today.toISOString().split('T')[0];
    };

    /**
     * Truncate text to a specific length
     * @param {string} text - Text to truncate
     * @param {number} maxLength - Maximum length
     * @returns {string} - Truncated text with ellipsis if needed
     */
    const truncateText = (text, maxLength = 50) => {
        if (!text) return '';
        if (text.length <= maxLength) return text;
        return text.substring(0, maxLength) + '...';
    };

    /**
     * Show a notification/toast message
     * @param {string} message - Message to display
     * @param {string} type - Type of message (success, error, info)
     */
    const showNotification = (message, type = 'info') => {
        // Create notification element
        const notification = document.createElement('div');
        notification.classList.add('notification', `notification-${type}`);
        notification.textContent = message;
        
        // Add to DOM
        document.body.appendChild(notification);
        
        // Trigger animation
        setTimeout(() => {
            notification.classList.add('show');
        }, 10);
        
        // Remove after delay
        setTimeout(() => {
            notification.classList.remove('show');
            setTimeout(() => {
                notification.remove();
            }, 300);
        }, 3000);
    };

    /**
     * Validate a weight entry
     * @param {Object} entry - Weight entry to validate
     * @returns {Object} - Validation result {valid, message}
     */
    const validateWeightEntry = (entry) => {
        if (!entry.date) {
            return { valid: false, message: 'Date is required' };
        }
        
        if (!entry.weight) {
            return { valid: false, message: 'Weight value is required' };
        }
        
        const weightValue = parseFloat(entry.weight);
        if (isNaN(weightValue) || weightValue <= 0) {
            return { valid: false, message: 'Weight must be a positive number' };
        }
        
        return { valid: true, message: 'Valid entry' };
    };

    /**
     * Calculate weight change and trend
     * @param {Array} weights - Array of weight entries
     * @returns {Object} - Statistics {totalChange, averageChange, trend}
     */
    const calculateWeightStats = (weights) => {
        if (!weights || weights.length < 2) {
            return { totalChange: 0, averageChange: 0, trend: 'neutral' };
        }
        
        // Sort by date (oldest first)
        const sortedWeights = [...weights].sort((a, b) => new Date(a.date) - new Date(b.date));
        
        const firstWeight = sortedWeights[0].weight;
        const lastWeight = sortedWeights[sortedWeights.length - 1].weight;
        const totalChange = lastWeight - firstWeight;
        
        // Calculate average change per day
        const daysDiff = Math.max(1, (new Date(sortedWeights[sortedWeights.length - 1].date) - new Date(sortedWeights[0].date)) / (1000 * 60 * 60 * 24));
        const averageChange = totalChange / daysDiff;
        
        // Determine trend
        let trend = 'neutral';
        if (totalChange < 0) {
            trend = 'down';
        } else if (totalChange > 0) {
            trend = 'up';
        }
        
        return {
            totalChange: totalChange.toFixed(2),
            averageChange: averageChange.toFixed(2),
            trend
        };
    };

    /**
     * Copy text to clipboard
     * @param {string} text - Text to copy
     * @returns {boolean} - Success status
     */
    const copyToClipboard = (text) => {
        try {
            // Use the modern navigator.clipboard API if available
            if (navigator.clipboard && navigator.clipboard.writeText) {
                navigator.clipboard.writeText(text);
                return true;
            }
            
            // Fallback for older browsers
            const textArea = document.createElement('textarea');
            textArea.value = text;
            textArea.style.position = 'fixed';
            document.body.appendChild(textArea);
            textArea.focus();
            textArea.select();
            
            const successful = document.execCommand('copy');
            document.body.removeChild(textArea);
            return successful;
        } catch (error) {
            console.error('Error copying to clipboard:', error);
            return false;
        }
    };

    /**
     * Sanitize HTML to prevent XSS attacks.
     * Replaces special characters with their HTML entities.
     * @param {string} text - The text to sanitize.
     * @returns {string} - The sanitized text.
     */
    const sanitizeHTML = (text) => {
        if (typeof text !== 'string') return '';
        return text.replace(/[&<>"']/g, function (match) {
            return {
                '&': '&amp;',
                '<': '&lt;',
                '>': '&gt;',
                '"': '&quot;',
                "'": '&#39;'
            }[match];
        });
    };

    // Return public API
    return {
        formatDate,
        getTodayDate,
        truncateText,
        showNotification,
        validateWeightEntry,
        calculateWeightStats,
        copyToClipboard,
        sanitizeHTML
    };
})();