document.addEventListener('DOMContentLoaded', function() {
    // Initialize app state
    if (!localStorage.getItem('shiftMasterData')) {
        localStorage.setItem('shiftMasterData', JSON.stringify({
            workers: [],
            shifts: [],
            schedule: []
        }));
    }
    
    // Load data from localStorage
    let appData = JSON.parse(localStorage.getItem('shiftMasterData'));
    
    // DOM Elements
    const addWorkerBtn = document.getElementById('addWorkerBtn');
    const workerForm = document.getElementById('workerForm');
    const saveWorker = document.getElementById('saveWorker');
    const cancelWorker = document.getElementById('cancelWorker');
    const workersList = document.getElementById('workersList');
    
    const addShiftBtn = document.getElementById('addShiftBtn');
    const shiftForm = document.getElementById('shiftForm');
    const saveShift = document.getElementById('saveShift');
    const cancelShift = document.getElementById('cancelShift');
    const shiftsList = document.getElementById('shiftsList');
    
    const generateSchedule = document.getElementById('generateSchedule');
    const scheduleResults = document.getElementById('scheduleResults');
    const scheduleTableBody = document.getElementById('scheduleTableBody');
    const saveSchedule = document.getElementById('saveSchedule');
    
    // Worker Management
    addWorkerBtn.addEventListener('click', () => {
        workerForm.classList.toggle('hidden');
    });
    
    cancelWorker.addEventListener('click', () => {
        workerForm.classList.add('hidden');
        document.getElementById('workerName').value = '';
        document.querySelectorAll('#workerForm input[type="checkbox"]').forEach(checkbox => {
            checkbox.checked = false;
        });
        document.getElementById('shiftPreference').value = 'any';
    });
    
    saveWorker.addEventListener('click', () => {
        const name = document.getElementById('workerName').value.trim();
        const daysAvailable = Array.from(document.querySelectorAll('#workerForm input[type="checkbox"]:checked'))
            .map(checkbox => checkbox.id);
        const shiftPreference = document.getElementById('shiftPreference').value;
        
        if (!name) {
            alert('Please enter a worker name');
            return;
        }
        
        const newWorker = {
            id: Date.now().toString(),
            name,
            daysAvailable,
            shiftPreference
        };
        
        appData.workers.push(newWorker);
        saveData();
        renderWorkers();
        workerForm.classList.add('hidden');
        document.getElementById('workerName').value = '';
        document.querySelectorAll('#workerForm input[type="checkbox"]').forEach(checkbox => {
            checkbox.checked = false;
        });
        document.getElementById('shiftPreference').value = 'any';
    });
    
    // Shift Management
    addShiftBtn.addEventListener('click', () => {
        shiftForm.classList.toggle('hidden');
    });
    
    cancelShift.addEventListener('click', () => {
        shiftForm.classList.add('hidden');
        document.getElementById('shiftDate').value = '';
        document.getElementById('shiftStart').value = '';
        document.getElementById('shiftEnd').value = '';
        document.getElementById('shiftRole').value = '';
    });
    
    saveShift.addEventListener('click', () => {
        const date = document.getElementById('shiftDate').value;
        const start = document.getElementById('shiftStart').value;
        const end = document.getElementById('shiftEnd').value;
        const role = document.getElementById('shiftRole').value.trim();
        
        if (!date || !start || !end || !role) {
            alert('Please fill all shift details');
            return;
        }
        
        const newShift = {
            id: Date.now().toString(),
            date,
            start,
            end,
            role,
            assignedWorker: null
        };
        
        appData.shifts.push(newShift);
        saveData();
        renderShifts();
        shiftForm.classList.add('hidden');
        document.getElementById('shiftDate').value = '';
        document.getElementById('shiftStart').value = '';
        document.getElementById('shiftEnd').value = '';
        document.getElementById('shiftRole').value = '';
    });
    
    // Schedule Generation
    generateSchedule.addEventListener('click', () => {
        if (appData.workers.length === 0 || appData.shifts.length === 0) {
            alert('Please add workers and shifts first');
            return;
        }
        
        // Show loading state
        const spinner = generateSchedule.querySelector('i');
        spinner.classList.remove('hidden');
        generateSchedule.disabled = true;
        
        // Simulate processing time
        setTimeout(() => {
            generateScheduleAlgorithm();
            spinner.classList.add('hidden');
            generateSchedule.disabled = false;
            scheduleResults.classList.remove('hidden');
        }, 1000);
    });
    
    saveSchedule.addEventListener('click', () => {
        saveData();
        alert('Schedule saved successfully!');
    });
    
    // Helper Functions
    function saveData() {
        localStorage.setItem('shiftMasterData', JSON.stringify(appData));
    }
    
    function renderWorkers() {
        if (appData.workers.length === 0) {
            workersList.innerHTML = '<p class="text-gray-500 italic">No workers added yet</p>';
            return;
        }
        
        workersList.innerHTML = '';
        appData.workers.forEach(worker => {
            const days = worker.daysAvailable.length > 0 
                ? worker.daysAvailable.join(', ') 
                : 'Not specified';
            const preference = worker.shiftPreference === 'any' 
                ? 'Any shift' 
                : worker.shiftPreference.charAt(0).toUpperCase() + worker.shiftPreference.slice(1);
            
            const workerElement = document.createElement('div');
            workerElement.className = 'worker-card bg-gray-50 p-3 rounded-lg border border-gray-200';
            workerElement.innerHTML = `
                <div class="flex justify-between items-start">
                    <div>
                        <h3 class="font-medium text-gray-800">${worker.name}</h3>
                        <p class="text-sm text-gray-600 mt-1"><span class="font-medium">Available:</span> ${days}</p>
                        <p class="text-sm text-gray-600"><span class="font-medium">Prefers:</span> ${preference}</p>
                    </div>
                    <button class="delete-worker text-red-500 hover:text-red-700" data-id="${worker.id}">
                        <i data-feather="trash-2" class="w-4 h-4"></i>
                    </button>
                </div>
            `;
            workersList.appendChild(workerElement);
        });
        
        // Add event listeners to delete buttons
        document.querySelectorAll('.delete-worker').forEach(button => {
            button.addEventListener('click', function() {
                const workerId = this.getAttribute('data-id');
                appData.workers = appData.workers.filter(worker => worker.id !== workerId);
                saveData();
                renderWorkers();
            });
        });
        
        feather.replace();
    }
    
    function renderShifts() {
        if (appData.shifts.length === 0) {
            shiftsList.innerHTML = '<p class="text-gray-500 italic">No shifts created yet</p>';
            return;
        }
        
        shiftsList.innerHTML = '';
        appData.shifts.forEach(shift => {
            const dateObj = new Date(shift.date);
            const formattedDate = dateObj.toLocaleDateString('en-US', { 
                weekday: 'short', 
                month: 'short', 
                day: 'numeric' 
            });
            
            const shiftElement = document.createElement('div');
            shiftElement.className = 'shift-card bg-gray-50 p-3 rounded-lg border border-gray-200';
            shiftElement.innerHTML = `
                <div class="flex justify-between items-start">
                    <div>
                        <h3 class="font-medium text-gray-800">${formattedDate}</h3>
                        <p class="text-sm text-gray-600 mt-1">${shift.start} - ${shift.end}</p>
                        <p class="text-sm text-gray-600"><span class="font-medium">Role:</span> ${shift.role}</p>
                        ${shift.assignedWorker ? `<p class="text-sm text-green-600 mt-1"><span class="font-medium">Assigned:</span> ${getWorkerName(shift.assignedWorker)}</p>` : ''}
                    </div>
                    <div class="flex space-x-2">
                        <button class="edit-shift text-blue-500 hover:text-blue-700" data-id="${shift.id}">
                            <i data-feather="edit" class="w-4 h-4"></i>
                        </button>
                        <button class="delete-shift text-red-500 hover:text-red-700" data-id="${shift.id}">
                            <i data-feather="trash-2" class="w-4 h-4"></i>
                        </button>
                    </div>
                </div>
            `;
            shiftsList.appendChild(shiftElement);
        });
        
        // Add event listeners to delete buttons
        document.querySelectorAll('.delete-shift').forEach(button => {
            button.addEventListener('click', function() {
                const shiftId = this.getAttribute('data-id');
                appData.shifts = appData.shifts.filter(shift => shift.id !== shiftId);
                saveData();
                renderShifts();
            });
        });
        
        feather.replace();
    }
    
    function getWorkerName(workerId) {
        const worker = appData.workers.find(w => w.id === workerId);
        return worker ? worker.name : 'Unknown';
    }
    
    function generateScheduleAlgorithm() {
        // Reset all assignments
        appData.shifts.forEach(shift => {
            shift.assignedWorker = null;
        });
        
        // Sort shifts by date and time
        const sortedShifts = [...appData.shifts].sort((a, b) => {
            const dateCompare = new Date(a.date) - new Date(b.date);
            if (dateCompare !== 0) return dateCompare;
            return a.start.localeCompare(b.start);
        });
        
        // Track assigned workers to prevent double-booking
        const assignedWorkers = new Set();
        
        // Assign workers to shifts
        sortedShifts.forEach(shift => {
            // Get the day of the week for this shift
            const shiftDate = new Date(shift.date);
            const dayOfWeek = ['sunday', 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday'][shiftDate.getDay()];
            
            // Determine shift type (morning, afternoon, night)
            const startHour = parseInt(shift.start.split(':')[0]);
            let shiftType = 'afternoon';
            if (startHour < 12) shiftType = 'morning';
            else if (startHour >= 22 || startHour < 6) shiftType = 'night';
            
            // Find available workers who:
            // 1. Are available on this day
            // 2. Match the shift preference (or have "any")
            // 3. Haven't been assigned to another shift in this schedule
            const availableWorkers = appData.workers.filter(worker => {
                return worker.daysAvailable.includes(dayOfWeek) && 
                       (worker.shiftPreference === 'any' || worker.shiftPreference === shiftType) &&
                       !assignedWorkers.has(worker.id);
            });
            
            // If we found available workers, assign the first one
            if (availableWorkers.length > 0) {
                const assignedWorker = availableWorkers[0];
                shift.assignedWorker = assignedWorker.id;
                assignedWorkers.add(assignedWorker.id);
            }
        });
        
        // Render the schedule
        renderSchedule();
        saveData();
    }
    
    function renderSchedule() {
        scheduleTableBody.innerHTML = '';
        
        // Group shifts by date
        const shiftsByDate = {};
        appData.shifts.forEach(shift => {
            const date = shift.date;
            if (!shiftsByDate[date]) {
                shiftsByDate[date] = [];
            }
            shiftsByDate[date].push(shift);
        });
        
        // Sort dates chronologically
        const sortedDates = Object.keys(shiftsByDate).sort((a, b) => new Date(a) - new Date(b));
        
        // Create table rows
        sortedDates.forEach(date => {
            const dateObj = new Date(date);
            const formattedDate = dateObj.toLocaleDateString('en-US', { 
                weekday: 'long', 
                month: 'long', 
                day: 'numeric' 
            });
            
            shiftsByDate[date].forEach(shift => {
                const row = document.createElement('tr');
                row.innerHTML = `
                    <td class="px-4 py-3 whitespace-nowrap text-sm text-gray-700">${formattedDate}</td>
                    <td class="px-4 py-3 whitespace-nowrap text-sm text-gray-700">${shift.start} - ${shift.end}</td>
                    <td class="px-4 py-3 whitespace-nowrap text-sm text-gray-700">${shift.role}</td>
                    <td class="px-4 py-3 whitespace-nowrap text-sm ${shift.assignedWorker ? 'text-green-600 font-medium' : 'text-red-500'}">
                        ${shift.assignedWorker ? getWorkerName(shift.assignedWorker) : 'Unassigned'}
                    </td>
                `;
                scheduleTableBody.appendChild(row);
            });
        });
    }
    
    // Initial render
    renderWorkers();
    renderShifts();
});