// Vehicle Maintenance Management System (VMMS)
// Main JavaScript File

class VMMS {
    constructor() {
        this.config = this.loadConfig();
        this.data = {
            vehicles: [],
            parts: [],
            logs: []
        };
        this.init();
    }

    // Initialize the application
    init() {
        this.setupEventListeners();
        this.loadPage('dashboard');
        
        // Load data if config exists
        if (this.config.sheetId) {
            this.loadAllData();
        }
    }

    // Setup all event listeners
    setupEventListeners() {
        // Navigation
        document.querySelectorAll('.nav-link').forEach(link => {
            link.addEventListener('click', (e) => {
                e.preventDefault();
                const page = e.target.getAttribute('data-page');
                this.loadPage(page);
            });
        });

        // Vehicle management
        document.getElementById('add-vehicle-btn').addEventListener('click', () => this.openVehicleModal());
        document.getElementById('vehicle-form').addEventListener('submit', (e) => this.saveVehicle(e));
        document.getElementById('vehicle-cancel-btn').addEventListener('click', () => this.closeModal('vehicle-modal'));
        document.getElementById('vehicle-modal-close').addEventListener('click', () => this.closeModal('vehicle-modal'));

        // Parts management
        document.getElementById('parts-vehicle-select').addEventListener('change', (e) => this.loadPartsByVehicle(e.target.value));
        document.getElementById('add-part-btn').addEventListener('click', () => this.openPartModal());
        document.getElementById('part-form').addEventListener('submit', (e) => this.savePart(e));
        document.getElementById('part-cancel-btn').addEventListener('click', () => this.closeModal('part-modal'));
        document.getElementById('part-modal-close').addEventListener('click', () => this.closeModal('part-modal'));

        // Logs management
        document.getElementById('logs-part-select').addEventListener('change', (e) => this.loadLogsByPart(e.target.value));
        document.getElementById('add-log-btn').addEventListener('click', () => this.openLogModal());
        document.getElementById('log-form').addEventListener('submit', (e) => this.saveLog(e));
        document.getElementById('log-cancel-btn').addEventListener('click', () => this.closeModal('log-modal'));
        document.getElementById('log-modal-close').addEventListener('click', () => this.closeModal('log-modal'));

        // Configuration
        document.getElementById('config-form').addEventListener('submit', (e) => this.saveConfig(e));
        document.getElementById('test-connection-btn').addEventListener('click', () => this.testConnection());

        // Modal click outside to close
        window.addEventListener('click', (e) => {
            if (e.target.classList.contains('modal')) {
                this.closeModal(e.target.id);
            }
        });
    }

    // Load and display specific page
    loadPage(pageId) {
        // Hide all pages
        document.querySelectorAll('.page').forEach(page => {
            page.classList.remove('active');
        });
        
        // Remove active class from nav links
        document.querySelectorAll('.nav-link').forEach(link => {
            link.classList.remove('active');
        });
        
        // Show selected page
        document.getElementById(pageId).classList.add('active');
        document.querySelector(`[data-page="${pageId}"]`).classList.add('active');
        
        // Load page-specific data
        switch (pageId) {
            case 'dashboard':
                this.loadDashboard();
                break;
            case 'vehicles':
                this.loadVehicles();
                break;
            case 'parts':
                this.loadParts();
                break;
            case 'logs':
                this.loadLogs();
                break;
            case 'config':
                this.loadConfigForm();
                break;
        }
    }

    // Configuration Management
    loadConfig() {
        const config = localStorage.getItem('vmms-config');
        return config ? JSON.parse(config) : {
            sheetId: '',
            vehiclesTab: 'Vehicles',
            partsTab: 'Parts',
            logsTab: 'MaintenanceLogs'
        };
    }

    saveConfig(e) {
        e.preventDefault();
        const formData = new FormData(e.target);
        
        this.config = {
            sheetId: formData.get('sheet-id') || document.getElementById('sheet-id').value,
            vehiclesTab: formData.get('vehicles-tab') || document.getElementById('vehicles-tab').value,
            partsTab: formData.get('parts-tab') || document.getElementById('parts-tab').value,
            logsTab: formData.get('logs-tab') || document.getElementById('logs-tab').value
        };
        
        localStorage.setItem('vmms-config', JSON.stringify(this.config));
        this.showToast('Configuration saved successfully!', 'success');
        
        // Load data after saving config
        this.loadAllData();
    }

    loadConfigForm() {
        document.getElementById('sheet-id').value = this.config.sheetId;
        document.getElementById('vehicles-tab').value = this.config.vehiclesTab;
        document.getElementById('parts-tab').value = this.config.partsTab;
        document.getElementById('logs-tab').value = this.config.logsTab;
    }

    async testConnection() {
        if (!this.config.sheetId) {
            this.showToast('Please enter a Sheet ID first', 'error');
            return;
        }

        this.showLoading();
        
        try {
            const url = `https://docs.google.com/spreadsheets/d/${this.config.sheetId}/gviz/tq?tqx=out:json&sheet=${this.config.vehiclesTab}`;
            const response = await fetch(url);
            
            if (response.ok) {
                this.showConnectionStatus('Connection successful! Sheet is accessible.', 'success');
            } else {
                throw new Error('Failed to connect');
            }
        } catch (error) {
            this.showConnectionStatus('Connection failed. Please check your Sheet ID and permissions.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    showConnectionStatus(message, type) {
        const statusDiv = document.getElementById('connection-status');
        statusDiv.textContent = message;
        statusDiv.className = `status-message ${type}`;
        statusDiv.style.display = 'block';
        
        setTimeout(() => {
            statusDiv.style.display = 'none';
        }, 5000);
    }

    // Data Management
    async loadAllData() {
        if (!this.config.sheetId) return;
        
        this.showLoading();
        
        try {
            await Promise.all([
                this.loadVehiclesData(),
                this.loadPartsData(),
                this.loadLogsData()
            ]);
            
            this.loadDashboard();
            this.showToast('Data loaded successfully!', 'success');
        } catch (error) {
            console.error('Error loading data:', error);
            this.showToast('Error loading data. Please check your configuration.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    async loadVehiclesData() {
        try {
            const url = `https://docs.google.com/spreadsheets/d/${this.config.sheetId}/gviz/tq?tqx=out:json&sheet=${this.config.vehiclesTab}`;
            const response = await fetch(url);
            const text = await response.text();
            const data = this.parseGoogleSheetsData(text);
            
            this.data.vehicles = data.map(row => ({
                id: row[0],
                name: row[1],
                model: row[2],
                year: row[3],
                registration: row[4],
                odometer: row[5],
                fuelType: row[6]
            }));
        } catch (error) {
            console.error('Error loading vehicles:', error);
            this.data.vehicles = [];
        }
    }

    async loadPartsData() {
        try {
            const url = `https://docs.google.com/spreadsheets/d/${this.config.sheetId}/gviz/tq?tqx=out:json&sheet=${this.config.partsTab}`;
            const response = await fetch(url);
            const text = await response.text();
            const data = this.parseGoogleSheetsData(text);
            
            this.data.parts = data.map(row => ({
                id: row[0],
                vehicleId: row[1],
                name: row[2],
                type: row[3],
                value: row[4],
                notes: row[5] || ''
            }));
        } catch (error) {
            console.error('Error loading parts:', error);
            this.data.parts = [];
        }
    }

    async loadLogsData() {
        try {
            const url = `https://docs.google.com/spreadsheets/d/${this.config.sheetId}/gviz/tq?tqx=out:json&sheet=${this.config.logsTab}`;
            const response = await fetch(url);
            const text = await response.text();
            const data = this.parseGoogleSheetsData(text);
            
            this.data.logs = data.map(row => ({
                id: row[0],
                partId: row[1],
                date: row[2],
                odometer: row[3],
                notes: row[4] || ''
            }));
        } catch (error) {
            console.error('Error loading logs:', error);
            this.data.logs = [];
        }
    }

    parseGoogleSheetsData(text) {
        try {
            // Remove Google Sheets wrapper
            const jsonString = text.match(/google\.visualization\.Query\.setResponse\((.*)\);/)[1];
            const data = JSON.parse(jsonString);
            
            if (!data.table || !data.table.rows) {
                return [];
            }
            
            return data.table.rows.map(row => 
                row.c ? row.c.map(cell => cell ? cell.v : '') : []
            );
        } catch (error) {
            console.error('Error parsing Google Sheets data:', error);
            return [];
        }
    }

    // Dashboard Management
    loadDashboard() {
        const totalVehicles = this.data.vehicles.length;
        const totalParts = this.data.parts.length;
        
        // Calculate overdue and upcoming maintenance
        const alerts = this.calculateMaintenanceAlerts();
        const overdueCount = alerts.filter(alert => alert.type === 'overdue').length;
        const upcomingCount = alerts.filter(alert => alert.type === 'upcoming').length;
        
        // Update dashboard cards
        document.getElementById('total-vehicles').textContent = totalVehicles;
        document.getElementById('total-parts').textContent = totalParts;
        document.getElementById('overdue-parts').textContent = overdueCount;
        document.getElementById('upcoming-parts').textContent = upcomingCount;
        
        // Display alerts
        this.displayAlerts(alerts);
    }

    calculateMaintenanceAlerts() {
        const alerts = [];
        const today = new Date();
        const oneMonthFromNow = new Date(today.getTime() + 30 * 24 * 60 * 60 * 1000);
        
        this.data.parts.forEach(part => {
            const vehicle = this.data.vehicles.find(v => v.id === part.vehicleId);
            if (!vehicle) return;
            
            const partLogs = this.data.logs.filter(log => log.partId === part.id);
            const lastLog = partLogs.sort((a, b) => new Date(b.date) - new Date(a.date))[0];
            
            if (!lastLog) {
                // No maintenance history - consider it overdue
                alerts.push({
                    type: 'overdue',
                    vehicle: vehicle.name,
                    part: part.name,
                    message: 'No maintenance history'
                });
                return;
            }
            
            const lastLogDate = new Date(lastLog.date);
            
            if (part.type === 'month') {
                const nextDueDate = new Date(lastLogDate.getTime() + parseInt(part.value) * 30 * 24 * 60 * 60 * 1000);
                
                if (nextDueDate < today) {
                    alerts.push({
                        type: 'overdue',
                        vehicle: vehicle.name,
                        part: part.name,
                        message: `Due ${Math.ceil((today - nextDueDate) / (1000 * 60 * 60 * 24))} days ago`
                    });
                } else if (nextDueDate < oneMonthFromNow) {
                    alerts.push({
                        type: 'upcoming',
                        vehicle: vehicle.name,
                        part: part.name,
                        message: `Due in ${Math.ceil((nextDueDate - today) / (1000 * 60 * 60 * 24))} days`
                    });
                }
            } else if (part.type === 'km') {
                const nextDueKm = parseInt(lastLog.odometer) + parseInt(part.value);
                const currentKm = parseInt(vehicle.odometer);
                
                if (currentKm >= nextDueKm) {
                    alerts.push({
                        type: 'overdue',
                        vehicle: vehicle.name,
                        part: part.name,
                        message: `Overdue by ${currentKm - nextDueKm} km`
                    });
                } else if ((nextDueKm - currentKm) <= 500) {
                    alerts.push({
                        type: 'upcoming',
                        vehicle: vehicle.name,
                        part: part.name,
                        message: `Due in ${nextDueKm - currentKm} km`
                    });
                }
            }
        });
        
        return alerts;
    }

    displayAlerts(alerts) {
        const container = document.getElementById('alerts-container');
        
        if (alerts.length === 0) {
            container.innerHTML = '<p class="no-alerts">No maintenance alerts at this time.</p>';
            return;
        }
        
        const alertsHtml = alerts.map(alert => `
            <div class="alert-item ${alert.type}">
                <div class="alert-icon">
                    ${alert.type === 'overdue' ? '🚨' : '⚠️'}
                </div>
                <div class="alert-content">
                    <h4>${alert.vehicle} - ${alert.part}</h4>
                    <p>${alert.message}</p>
                </div>
            </div>
        `).join('');
        
        container.innerHTML = alertsHtml;
    }

    // Vehicle Management
    loadVehicles() {
        const tbody = document.querySelector('#vehicles-table tbody');
        
        if (this.data.vehicles.length === 0) {
            tbody.innerHTML = '<tr class="no-data"><td colspan="8">No vehicles found. Add your first vehicle!</td></tr>';
            return;
        }
        
        const vehiclesHtml = this.data.vehicles.map(vehicle => `
            <tr>
                <td>${vehicle.id}</td>
                <td>${vehicle.name}</td>
                <td>${vehicle.model}</td>
                <td>${vehicle.year}</td>
                <td>${vehicle.registration}</td>
                <td>${vehicle.odometer}</td>
                <td>${vehicle.fuelType}</td>
                <td>
                    <div class="action-buttons">
                        <button class="btn btn-warning btn-small" onclick="vmms.editVehicle('${vehicle.id}')">Edit</button>
                        <button class="btn btn-danger btn-small" onclick="vmms.deleteVehicle('${vehicle.id}')">Delete</button>
                    </div>
                </td>
            </tr>
        `).join('');
        
        tbody.innerHTML = vehiclesHtml;
    }

    openVehicleModal(vehicleId = null) {
        const modal = document.getElementById('vehicle-modal');
        const title = document.getElementById('vehicle-modal-title');
        const form = document.getElementById('vehicle-form');
        
        form.reset();
        
        if (vehicleId) {
            const vehicle = this.data.vehicles.find(v => v.id === vehicleId);
            if (vehicle) {
                title.textContent = 'Edit Vehicle';
                document.getElementById('vehicle-id').value = vehicle.id;
                document.getElementById('vehicle-name').value = vehicle.name;
                document.getElementById('vehicle-model').value = vehicle.model;
                document.getElementById('vehicle-year').value = vehicle.year;
                document.getElementById('vehicle-registration').value = vehicle.registration;
                document.getElementById('vehicle-odometer').value = vehicle.odometer;
                document.getElementById('vehicle-fuel-type').value = vehicle.fuelType;
            }
        } else {
            title.textContent = 'Add Vehicle';
            document.getElementById('vehicle-id').value = '';
        }
        
        modal.style.display = 'block';
    }

    async saveVehicle(e) {
        e.preventDefault();
        
        const formData = new FormData(e.target);
        const vehicleId = formData.get('vehicle-id') || document.getElementById('vehicle-id').value;
        const isEdit = !!vehicleId;
        
        const vehicle = {
            id: vehicleId || this.generateId('V'),
            name: formData.get('vehicle-name') || document.getElementById('vehicle-name').value,
            model: formData.get('vehicle-model') || document.getElementById('vehicle-model').value,
            year: formData.get('vehicle-year') || document.getElementById('vehicle-year').value,
            registration: formData.get('vehicle-registration') || document.getElementById('vehicle-registration').value,
            odometer: formData.get('vehicle-odometer') || document.getElementById('vehicle-odometer').value,
            fuelType: formData.get('vehicle-fuel-type') || document.getElementById('vehicle-fuel-type').value
        };
        
        try {
            this.showLoading();
            
            if (isEdit) {
                await this.updateVehicleInSheet(vehicle);
                const index = this.data.vehicles.findIndex(v => v.id === vehicleId);
                this.data.vehicles[index] = vehicle;
            } else {
                await this.addVehicleToSheet(vehicle);
                this.data.vehicles.push(vehicle);
            }
            
            this.closeModal('vehicle-modal');
            this.loadVehicles();
            this.updateVehicleSelects();
            this.showToast(isEdit ? 'Vehicle updated successfully!' : 'Vehicle added successfully!', 'success');
        } catch (error) {
            console.error('Error saving vehicle:', error);
            this.showToast('Error saving vehicle. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    async addVehicleToSheet(vehicle) {
        // This is a placeholder - in a real implementation, you would use Google Sheets API
        // For now, we'll simulate the operation
        return new Promise(resolve => setTimeout(resolve, 500));
    }

    async updateVehicleInSheet(vehicle) {
        // This is a placeholder - in a real implementation, you would use Google Sheets API
        return new Promise(resolve => setTimeout(resolve, 500));
    }

    editVehicle(vehicleId) {
        this.openVehicleModal(vehicleId);
    }

    async deleteVehicle(vehicleId) {
        if (!confirm('Are you sure you want to delete this vehicle? This will also delete all associated parts and logs.')) {
            return;
        }
        
        try {
            this.showLoading();
            
            // Remove vehicle and associated data
            this.data.vehicles = this.data.vehicles.filter(v => v.id !== vehicleId);
            this.data.parts = this.data.parts.filter(p => p.vehicleId !== vehicleId);
            
            // Remove logs for deleted parts
            const partIds = this.data.parts.filter(p => p.vehicleId === vehicleId).map(p => p.id);
            this.data.logs = this.data.logs.filter(l => !partIds.includes(l.partId));
            
            this.loadVehicles();
            this.updateVehicleSelects();
            this.showToast('Vehicle deleted successfully!', 'success');
        } catch (error) {
            console.error('Error deleting vehicle:', error);
            this.showToast('Error deleting vehicle. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    // Parts Management
    loadParts() {
        this.updateVehicleSelects();
        const selectedVehicleId = document.getElementById('parts-vehicle-select').value;
        this.loadPartsByVehicle(selectedVehicleId);
    }

    updateVehicleSelects() {
        const selects = ['parts-vehicle-select'];
        
        selects.forEach(selectId => {
            const select = document.getElementById(selectId);
            const currentValue = select.value;
            
            select.innerHTML = '<option value="">Select Vehicle</option>';
            
            this.data.vehicles.forEach(vehicle => {
                const option = document.createElement('option');
                option.value = vehicle.id;
                option.textContent = `${vehicle.name} (${vehicle.registration})`;
                select.appendChild(option);
            });
            
            if (currentValue && this.data.vehicles.find(v => v.id === currentValue)) {
                select.value = currentValue;
            }
        });
    }

    loadPartsByVehicle(vehicleId) {
        const tbody = document.querySelector('#parts-table tbody');
        const addButton = document.getElementById('add-part-btn');
        
        if (!vehicleId) {
            tbody.innerHTML = '<tr class="no-data"><td colspan="7">Select a vehicle to view its parts.</td></tr>';
            addButton.disabled = true;
            return;
        }
        
        addButton.disabled = false;
        
        const vehicleParts = this.data.parts.filter(p => p.vehicleId === vehicleId);
        
        if (vehicleParts.length === 0) {
            tbody.innerHTML = '<tr class="no-data"><td colspan="7">No parts found for this vehicle. Add the first part!</td></tr>';
            return;
        }
        
        const partsHtml = vehicleParts.map(part => {
            const vehicle = this.data.vehicles.find(v => v.id === part.vehicleId);
            return `
                <tr>
                    <td>${part.id}</td>
                    <td>${vehicle ? vehicle.name : 'Unknown'}</td>
                    <td>${part.name}</td>
                    <td>${this.formatReplacementType(part.type)}</td>
                    <td>${part.value}</td>
                    <td>${part.notes}</td>
                    <td>
                        <div class="action-buttons">
                            <button class="btn btn-warning btn-small" onclick="vmms.editPart('${part.id}')">Edit</button>
                            <button class="btn btn-danger btn-small" onclick="vmms.deletePart('${part.id}')">Delete</button>
                        </div>
                    </td>
                </tr>
            `;
        }).join('');
        
        tbody.innerHTML = partsHtml;
        this.updatePartSelects();
    }

    formatReplacementType(type) {
        switch (type) {
            case 'month': return 'Time-based (months)';
            case 'km': return 'Distance-based (km)';
            case 'custom': return 'Custom';
            default: return type;
        }
    }

    openPartModal(partId = null) {
        const selectedVehicleId = document.getElementById('parts-vehicle-select').value;
        
        if (!selectedVehicleId && !partId) {
            this.showToast('Please select a vehicle first', 'warning');
            return;
        }
        
        const modal = document.getElementById('part-modal');
        const title = document.getElementById('part-modal-title');
        const form = document.getElementById('part-form');
        
        form.reset();
        
        if (partId) {
            const part = this.data.parts.find(p => p.id === partId);
            if (part) {
                title.textContent = 'Edit Part';
                document.getElementById('part-id').value = part.id;
                document.getElementById('part-vehicle-id').value = part.vehicleId;
                document.getElementById('part-name').value = part.name;
                document.getElementById('part-replacement-type').value = part.type;
                document.getElementById('part-replacement-value').value = part.value;
                document.getElementById('part-notes').value = part.notes;
            }
        } else {
            title.textContent = 'Add Part';
            document.getElementById('part-id').value = '';
            document.getElementById('part-vehicle-id').value = selectedVehicleId;
        }
        
        modal.style.display = 'block';
    }

    async savePart(e) {
        e.preventDefault();
        
        const formData = new FormData(e.target);
        const partId = formData.get('part-id') || document.getElementById('part-id').value;
        const isEdit = !!partId;
        
        const part = {
            id: partId || this.generateId('P'),
            vehicleId: formData.get('part-vehicle-id') || document.getElementById('part-vehicle-id').value,
            name: formData.get('part-name') || document.getElementById('part-name').value,
            type: formData.get('part-replacement-type') || document.getElementById('part-replacement-type').value,
            value: formData.get('part-replacement-value') || document.getElementById('part-replacement-value').value,
            notes: formData.get('part-notes') || document.getElementById('part-notes').value
        };
        
        try {
            this.showLoading();
            
            if (isEdit) {
                const index = this.data.parts.findIndex(p => p.id === partId);
                this.data.parts[index] = part;
            } else {
                this.data.parts.push(part);
            }
            
            this.closeModal('part-modal');
            this.loadPartsByVehicle(part.vehicleId);
            this.updatePartSelects();
            this.showToast(isEdit ? 'Part updated successfully!' : 'Part added successfully!', 'success');
        } catch (error) {
            console.error('Error saving part:', error);
            this.showToast('Error saving part. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    editPart(partId) {
        this.openPartModal(partId);
    }

    async deletePart(partId) {
        if (!confirm('Are you sure you want to delete this part? This will also delete all associated maintenance logs.')) {
            return;
        }
        
        try {
            this.showLoading();
            
            const part = this.data.parts.find(p => p.id === partId);
            
            // Remove part and associated logs
            this.data.parts = this.data.parts.filter(p => p.id !== partId);
            this.data.logs = this.data.logs.filter(l => l.partId !== partId);
            
            this.loadPartsByVehicle(part.vehicleId);
            this.updatePartSelects();
            this.showToast('Part deleted successfully!', 'success');
        } catch (error) {
            console.error('Error deleting part:', error);
            this.showToast('Error deleting part. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    // Logs Management
    loadLogs() {
        this.updatePartSelects();
        const selectedPartId = document.getElementById('logs-part-select').value;
        this.loadLogsByPart(selectedPartId);
    }

    updatePartSelects() {
        const select = document.getElementById('logs-part-select');
        const currentValue = select.value;
        
        select.innerHTML = '<option value="">Select Part</option>';
        
        this.data.parts.forEach(part => {
            const vehicle = this.data.vehicles.find(v => v.id === part.vehicleId);
            const option = document.createElement('option');
            option.value = part.id;
            option.textContent = `${vehicle ? vehicle.name : 'Unknown'} - ${part.name}`;
            select.appendChild(option);
        });
        
        if (currentValue && this.data.parts.find(p => p.id === currentValue)) {
            select.value = currentValue;
        }
    }

    loadLogsByPart(partId) {
        const tbody = document.querySelector('#logs-table tbody');
        const addButton = document.getElementById('add-log-btn');
        
        if (!partId) {
            tbody.innerHTML = '<tr class="no-data"><td colspan="7">Select a part to view its maintenance logs.</td></tr>';
            addButton.disabled = true;
            return;
        }
        
        addButton.disabled = false;
        
        const partLogs = this.data.logs.filter(l => l.partId === partId);
        
        if (partLogs.length === 0) {
            tbody.innerHTML = '<tr class="no-data"><td colspan="7">No maintenance logs found for this part. Add the first log!</td></tr>';
            return;
        }
        
        const logsHtml = partLogs.map(log => {
            const part = this.data.parts.find(p => p.id === log.partId);
            const vehicle = part ? this.data.vehicles.find(v => v.id === part.vehicleId) : null;
            
            return `
                <tr>
                    <td>${log.id}</td>
                    <td>${part ? part.name : 'Unknown'}</td>
                    <td>${vehicle ? vehicle.name : 'Unknown'}</td>
                    <td>${this.formatDate(log.date)}</td>
                    <td>${log.odometer}</td>
                    <td>${log.notes}</td>
                    <td>
                        <div class="action-buttons">
                            <button class="btn btn-warning btn-small" onclick="vmms.editLog('${log.id}')">Edit</button>
                            <button class="btn btn-danger btn-small" onclick="vmms.deleteLog('${log.id}')">Delete</button>
                        </div>
                    </td>
                </tr>
            `;
        }).join('');
        
        tbody.innerHTML = logsHtml;
    }

    openLogModal(logId = null) {
        const selectedPartId = document.getElementById('logs-part-select').value;
        
        if (!selectedPartId && !logId) {
            this.showToast('Please select a part first', 'warning');
            return;
        }
        
        const modal = document.getElementById('log-modal');
        const title = document.getElementById('log-modal-title');
        const form = document.getElementById('log-form');
        
        form.reset();
        
        if (logId) {
            const log = this.data.logs.find(l => l.id === logId);
            if (log) {
                title.textContent = 'Edit Maintenance Log';
                document.getElementById('log-id').value = log.id;
                document.getElementById('log-part-id').value = log.partId;
                document.getElementById('log-date').value = log.date;
                document.getElementById('log-odometer').value = log.odometer;
                document.getElementById('log-notes').value = log.notes;
            }
        } else {
            title.textContent = 'Add Maintenance Log';
            document.getElementById('log-id').value = '';
            document.getElementById('log-part-id').value = selectedPartId;
            
            // Set today's date as default
            const today = new Date().toISOString().split('T')[0];
            document.getElementById('log-date').value = today;
        }
        
        modal.style.display = 'block';
    }

    async saveLog(e) {
        e.preventDefault();
        
        const formData = new FormData(e.target);
        const logId = formData.get('log-id') || document.getElementById('log-id').value;
        const isEdit = !!logId;
        
        const log = {
            id: logId || this.generateId('L'),
            partId: formData.get('log-part-id') || document.getElementById('log-part-id').value,
            date: formData.get('log-date') || document.getElementById('log-date').value,
            odometer: formData.get('log-odometer') || document.getElementById('log-odometer').value,
            notes: formData.get('log-notes') || document.getElementById('log-notes').value
        };
        
        try {
            this.showLoading();
            
            if (isEdit) {
                const index = this.data.logs.findIndex(l => l.id === logId);
                this.data.logs[index] = log;
            } else {
                this.data.logs.push(log);
            }
            
            this.closeModal('log-modal');
            this.loadLogsByPart(log.partId);
            this.showToast(isEdit ? 'Log updated successfully!' : 'Log added successfully!', 'success');
        } catch (error) {
            console.error('Error saving log:', error);
            this.showToast('Error saving log. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    editLog(logId) {
        this.openLogModal(logId);
    }

    async deleteLog(logId) {
        if (!confirm('Are you sure you want to delete this maintenance log?')) {
            return;
        }
        
        try {
            this.showLoading();
            
            const log = this.data.logs.find(l => l.id === logId);
            this.data.logs = this.data.logs.filter(l => l.id !== logId);
            
            this.loadLogsByPart(log.partId);
            this.showToast('Log deleted successfully!', 'success');
        } catch (error) {
            console.error('Error deleting log:', error);
            this.showToast('Error deleting log. Please try again.', 'error');
        } finally {
            this.hideLoading();
        }
    }

    // Utility Functions
    generateId(prefix) {
        const items = this.data[prefix === 'V' ? 'vehicles' : prefix === 'P' ? 'parts' : 'logs'];
        const numbers = items
            .map(item => parseInt(item.id.substring(1)))
            .filter(num => !isNaN(num))
            .sort((a, b) => b - a);
        
        const nextNumber = numbers.length > 0 ? numbers[0] + 1 : 1;
        return `${prefix}${nextNumber}`;
    }

    formatDate(dateString) {
        if (!dateString) return '';
        const date = new Date(dateString);
        return date.toLocaleDateString();
    }

    closeModal(modalId) {
        document.getElementById(modalId).style.display = 'none';
    }

    showLoading() {
        document.getElementById('loading-overlay').style.display = 'flex';
    }

    hideLoading() {
        document.getElementById('loading-overlay').style.display = 'none';
    }

    showToast(message, type = 'info') {
        const toastContainer = document.getElementById('toast-container');
        
        const toast = document.createElement('div');
        toast.className = `toast ${type}`;
        toast.innerHTML = `
            <div class="toast-title">${type.charAt(0).toUpperCase() + type.slice(1)}</div>
            <div class="toast-message">${message}</div>
        `;
        
        toastContainer.appendChild(toast);
        
        // Auto-remove toast after 5 seconds
        setTimeout(() => {
            if (toast.parentNode) {
                toast.parentNode.removeChild(toast);
            }
        }, 5000);
        
        // Add click to dismiss
        toast.addEventListener('click', () => {
            if (toast.parentNode) {
                toast.parentNode.removeChild(toast);
            }
        });
    }
}

// Initialize the application when the DOM is loaded
document.addEventListener('DOMContentLoaded', () => {
    window.vmms = new VMMS();
});

// Additional helper functions for Google Sheets integration
// Note: In a real implementation, you would need to set up proper Google Sheets API integration
// This includes authentication, proper API calls, and error handling

class GoogleSheetsAPI {
    constructor(sheetId, apiKey = null) {
        this.sheetId = sheetId;
        this.apiKey = apiKey;
        this.baseUrl = 'https://sheets.googleapis.com/v4/spreadsheets';
    }

    async readSheet(sheetName) {
        try {
            const url = this.apiKey 
                ? `${this.baseUrl}/${this.sheetId}/values/${sheetName}?key=${this.apiKey}`
                : `https://docs.google.com/spreadsheets/d/${this.sheetId}/gviz/tq?tqx=out:json&sheet=${sheetName}`;
            
            const response = await fetch(url);
            
            if (!response.ok) {
                throw new Error(`HTTP error! status: ${response.status}`);
            }
            
            if (this.apiKey) {
                const data = await response.json();
                return data.values || [];
            } else {
                const text = await response.text();
                return this.parseGoogleSheetsData(text);
            }
        } catch (error) {
            console.error(`Error reading sheet ${sheetName}:`, error);
            throw error;
        }
    }

    async appendToSheet(sheetName, values) {
        if (!this.apiKey) {
            throw new Error('API key required for write operations');
        }
        
        try {
            const url = `${this.baseUrl}/${this.sheetId}/values/${sheetName}!A:A:append?valueInputOption=USER_ENTERED&key=${this.apiKey}`;
            
            const response = await fetch(url, {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                },
                body: JSON.stringify({
                    values: [values]
                })
            });
            
            if (!response.ok) {
                throw new Error(`HTTP error! status: ${response.status}`);
            }
            
            return await response.json();
        } catch (error) {
            console.error(`Error appending to sheet ${sheetName}:`, error);
            throw error;
        }
    }

    async updateSheet(sheetName, range, values) {
        if (!this.apiKey) {
            throw new Error('API key required for write operations');
        }
        
        try {
            const url = `${this.baseUrl}/${this.sheetId}/values/${sheetName}!${range}?valueInputOption=USER_ENTERED&key=${this.apiKey}`;
            
            const response = await fetch(url, {
                method: 'PUT',
                headers: {
                    'Content-Type': 'application/json',
                },
                body: JSON.stringify({
                    values: [values]
                })
            });
            
            if (!response.ok) {
                throw new Error(`HTTP error! status: ${response.status}`);
            }
            
            return await response.json();
        } catch (error) {
            console.error(`Error updating sheet ${sheetName}:`, error);
            throw error;
        }
    }

    parseGoogleSheetsData(text) {
        try {
            const jsonString = text.match(/google\.visualization\.Query\.setResponse\((.*)\);/)[1];
            const data = JSON.parse(jsonString);
            
            if (!data.table || !data.table.rows) {
                return [];
            }
            
            return data.table.rows.map(row => 
                row.c ? row.c.map(cell => cell ? cell.v : '') : []
            );
        } catch (error) {
            console.error('Error parsing Google Sheets data:', error);
            return [];
        }
    }
}

// Export for potential use in modules
if (typeof module !== 'undefined' && module.exports) {
    module.exports = { VMMS, GoogleSheetsAPI };
}