/**
 * Utility Functions
 * Date handling, holidays, and common helpers
 */

// Holiday cache: { year: Set of date strings }
const holidayCache = {};

/**
 * Load holidays for a year from API (called automatically)
 */
async function loadHolidaysForYear(year) {
    if (holidayCache[year]) return;

    try {
        const response = await fetch(`/api/auth/holidays/${year}`);
        if (response.ok) {
            const holidays = await response.json();
            holidayCache[year] = new Set(holidays.map(h => h.date));
        }
    } catch (e) {
        // Fall back to local calculation if API fails
        console.warn('Holiday API failed, using local fallback');
    }
}

/**
 * Calculate Easter Sunday using Computus algorithm (fallback)
 */
function calculateEaster(year) {
    const a = year % 19;
    const b = Math.floor(year / 100);
    const c = year % 100;
    const d = Math.floor(b / 4);
    const e = b % 4;
    const f = Math.floor((b + 8) / 25);
    const g = Math.floor((b - f + 1) / 3);
    const h = (19 * a + b - d - g + 15) % 30;
    const i = Math.floor(c / 4);
    const k = c % 4;
    const l = (32 + 2 * e + 2 * i - h - k) % 7;
    const m = Math.floor((a + 11 * h + 22 * l) / 451);
    const month = Math.floor((h + l - 7 * m + 114) / 31);
    const day = ((h + l - 7 * m + 114) % 31) + 1;
    return new Date(year, month - 1, day);
}

/**
 * Check if a date is an Italian holiday
 * Uses cached API data if available, otherwise falls back to local calculation
 */
function isItalianHoliday(date) {
    const year = date.getFullYear();
    const dateStr = formatDate(date);

    // Check cache first
    if (holidayCache[year] && holidayCache[year].has(dateStr)) {
        return true;
    }

    // Fallback: local calculation
    const month = date.getMonth() + 1;
    const day = date.getDate();

    const fixedHolidays = [
        [1, 1], [1, 6], [4, 25], [5, 1], [6, 2],
        [8, 15], [11, 1], [12, 8], [12, 25], [12, 26]
    ];

    for (const [hm, hd] of fixedHolidays) {
        if (month === hm && day === hd) return true;
    }

    // Easter Monday
    const easter = calculateEaster(year);
    const easterMonday = new Date(easter);
    easterMonday.setDate(easter.getDate() + 1);
    if (date.getMonth() === easterMonday.getMonth() && date.getDate() === easterMonday.getDate()) {
        return true;
    }

    return false;
}

/**
 * Format date as YYYY-MM-DD
 */
function formatDate(date) {
    const year = date.getFullYear();
    const month = String(date.getMonth() + 1).padStart(2, '0');
    const day = String(date.getDate()).padStart(2, '0');
    return `${year}-${month}-${day}`;
}

/**
 * Format date for display
 */
function formatDateDisplay(dateStr) {
    const date = new Date(dateStr + 'T12:00:00');
    return date.toLocaleDateString('en-US', {
        weekday: 'short',
        month: 'short',
        day: 'numeric'
    });
}

/**
 * Get month name
 */
function getMonthName(month) {
    const months = [
        'January', 'February', 'March', 'April', 'May', 'June',
        'July', 'August', 'September', 'October', 'November', 'December'
    ];
    return months[month];
}

/**
 * Get day name
 */
function getDayName(dayIndex) {
    const days = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
    return days[dayIndex];
}

/**
 * Get days in month
 */
function getDaysInMonth(year, month) {
    return new Date(year, month + 1, 0).getDate();
}

/**
 * Get start of week for a date
 */
function getWeekStart(date, weekStartDay = 0) {
    const d = new Date(date);
    const day = d.getDay();
    const diff = (day - weekStartDay + 7) % 7;
    d.setDate(d.getDate() - diff);
    d.setHours(0, 0, 0, 0);
    return d;
}

/**
 * Format date as short display (e.g., "Nov 26")
 */
function formatDateShort(date) {
    return date.toLocaleDateString('en-US', {
        month: 'short',
        day: 'numeric'
    });
}

/**
 * Show a temporary message (creates toast if no container)
 */
function showMessage(message, type = 'success', duration = 3000) {
    // Create toast container if it doesn't exist
    let toastContainer = document.getElementById('toastContainer');
    if (!toastContainer) {
        toastContainer = document.createElement('div');
        toastContainer.id = 'toastContainer';
        toastContainer.style.cssText = `
            position: fixed;
            top: 1rem;
            right: 1rem;
            z-index: 9999;
            display: flex;
            flex-direction: column;
            gap: 0.5rem;
        `;
        document.body.appendChild(toastContainer);
    }

    const toast = document.createElement('div');
    toast.className = `message ${type}`;
    toast.style.cssText = `
        padding: 0.75rem 1rem;
        border-radius: 6px;
        box-shadow: 0 2px 8px rgba(0,0,0,0.15);
        animation: slideIn 0.2s ease;
    `;
    toast.textContent = message;
    toastContainer.appendChild(toast);

    if (duration > 0) {
        setTimeout(() => {
            toast.style.animation = 'slideOut 0.2s ease';
            setTimeout(() => toast.remove(), 200);
        }, duration);
    }
}

/**
 * Close modal when clicking outside
 */
function setupModalClose(modalId) {
    const modal = document.getElementById(modalId);
    if (modal) {
        modal.addEventListener('click', (e) => {
            if (e.target.id === modalId) {
                modal.style.display = 'none';
            }
        });
    }
}

// Export utilities
window.utils = {
    loadHolidaysForYear,
    isItalianHoliday,
    formatDate,
    formatDateDisplay,
    formatDateShort,
    getMonthName,
    getDayName,
    getDaysInMonth,
    getWeekStart,
    showMessage,
    setupModalClose
};