/**
 * Charts Module
 * Handles data visualization and charts
 */
const Charts = (() => {
    // Chart configuration
    let weightChartInstance = null;
    let dateFilter = {
        startDate: null,
        endDate: null
    };

    /**
     * Initialize charts
     */
    const init = () => {
        // Load Chart.js from CDN if not available
        if (typeof Chart === 'undefined') {
            loadChartJS().then(() => {
                renderWeightChart();
            }).catch(error => {
                console.error('Failed to load Chart.js:', error);
                showChartError('Failed to load chart library');
            });
        } else {
            renderWeightChart();
        }
    };

    /**
     * Load Chart.js and required adapters from CDN
     * @returns {Promise} - Resolves when Chart.js is loaded
     */
    const loadChartJS = () => {
        return new Promise((resolve, reject) => {
            // First load Chart.js core
            const chartScript = document.createElement('script');
            chartScript.src = 'https://cdn.jsdelivr.net/npm/chart.js@3.9.1/dist/chart.min.js';
            chartScript.crossOrigin = 'anonymous';
            
            chartScript.onload = () => {
                // Then load the date adapter
                const adapterScript = document.createElement('script');
                adapterScript.src = 'https://cdn.jsdelivr.net/npm/chartjs-adapter-date-fns@2.0.0/dist/chartjs-adapter-date-fns.bundle.min.js';
                adapterScript.crossOrigin = 'anonymous';
                
                adapterScript.onload = () => resolve();
                adapterScript.onerror = () => reject(new Error('Failed to load Chart.js date adapter'));
                
                document.head.appendChild(adapterScript);
            };
            
            chartScript.onerror = () => reject(new Error('Failed to load Chart.js'));
            document.head.appendChild(chartScript);
        });
    };

    /**
     * Render weight chart
     */
    const renderWeightChart = () => {
        if (typeof Chart === 'undefined') {
            return;
        }

        const chartContainer = document.getElementById('weight-chart');
        
        // Get weight data with filters applied
        const weights = DataManager.getWeights(dateFilter);
        
        if (weights.length === 0) {
            chartContainer.innerHTML = '<div class="placeholder-message">No weight data available for the selected period</div>';
            return;
        }
        
        // Sort by date (oldest first for chart)
        const sortedWeights = [...weights].sort((a, b) => new Date(a.date) - new Date(b.date));
        
        // Prepare data for the chart
        const labels = sortedWeights.map(entry => entry.date);
        const data = sortedWeights.map(entry => entry.weight);
        
        // Clear existing chart
        if (weightChartInstance) {
            weightChartInstance.destroy();
        }
        
        // Create canvas element
        chartContainer.innerHTML = '<canvas id="weight-chart-canvas"></canvas>';
        const ctx = document.getElementById('weight-chart-canvas').getContext('2d');
        
        // Create new chart
        weightChartInstance = new Chart(ctx, {
            type: 'line',
            data: {
                labels: labels,
                datasets: [{
                    label: 'Weight (kg)',
                    data: data,
                    fill: false,
                    borderColor: '#4a6fa5',
                    tension: 0.1,
                    pointBackgroundColor: '#4a6fa5',
                    pointRadius: 5,
                    pointHoverRadius: 7
                }]
            },
            options: {
                responsive: true,
                maintainAspectRatio: false,
                scales: {
                    x: {
                        type: 'time',
                        time: {
                            unit: 'day',
                            displayFormats: {
                                day: 'MMM d'
                            }
                        },
                        title: {
                            display: true,
                            text: 'Date'
                        }
                    },
                    y: {
                        title: {
                            display: true,
                            text: 'Weight (kg)'
                        },
                        beginAtZero: false
                    }
                },
                plugins: {
                    legend: {
                        display: true,
                        position: 'top'
                    },
                    tooltip: {
                        callbacks: {
                            title: function(tooltipItems) {
                                const date = new Date(tooltipItems[0].label);
                                return date.toLocaleDateString('en-US', { 
                                    year: 'numeric', 
                                    month: 'long', 
                                    day: 'numeric' 
                                });
                            }
                        }
                    }
                }
            }
        });
    };

    /**
     * Update the date filter and refresh the chart
     * @param {string} startDate - Start date in YYYY-MM-DD format
     * @param {string} endDate - End date in YYYY-MM-DD format
     */
    const updateDateFilter = (startDate, endDate) => {
        dateFilter.startDate = startDate || null;
        dateFilter.endDate = endDate || null;
        renderWeightChart();
    };

    /**
     * Show error message in chart container
     * @param {string} message - Error message
     */
    const showChartError = (message) => {
        const chartContainer = document.getElementById('weight-chart');
        chartContainer.innerHTML = `<div class="placeholder-message error">${message}</div>`;
    };

    // Return public API
    return {
        init,
        renderWeightChart,
        updateDateFilter
    };
})();