import React, { useState, useEffect, useRef, useCallback } from 'react';
import { createPortal } from 'react-dom';
import { format, addMonths, subMonths, startOfMonth, endOfMonth, startOfWeek, endOfWeek, addDays, isSameMonth, isSameDay } from 'date-fns';
import { enUS, de, fr, es, it } from 'date-fns/locale';

interface SimpleDatePickerProps {
    selected: Date;
    onSelect: (date: Date) => void;
    onClose: () => void;
    language?: string;
    anchorRef?: React.RefObject<HTMLElement | null>;
}

export default function SimpleDatePicker({ selected, onSelect, onClose, language = 'en', anchorRef }: SimpleDatePickerProps) {
    const [currentMonth, setCurrentMonth] = useState(new Date(selected));
    const modalRef = useRef<HTMLDivElement>(null);
    const localeMap: Record<string, typeof enUS> = { de, fr, es, it };
    const locale = localeMap[language] || enUS;
    const [position, setPosition] = useState<{ top: number; left: number } | null>(null);

    const updatePosition = useCallback(() => {
        if (anchorRef?.current) {
            const rect = anchorRef.current.getBoundingClientRect();
            setPosition({
                top: rect.bottom + 8,
                left: rect.left + rect.width / 2 - 144, // 144 = half of 18rem (288px)
            });
        }
    }, [anchorRef]);

    useEffect(() => {
        updatePosition();
        window.addEventListener('resize', updatePosition);
        window.addEventListener('scroll', updatePosition, true);
        return () => {
            window.removeEventListener('resize', updatePosition);
            window.removeEventListener('scroll', updatePosition, true);
        };
    }, [updatePosition]);

    useEffect(() => {
        const handleClickOutside = (event: MouseEvent) => {
            if (modalRef.current && !modalRef.current.contains(event.target as Node)) {
                // Also check if click is on the anchor/trigger button
                if (anchorRef?.current && anchorRef.current.contains(event.target as Node)) return;
                onClose();
            }
        };
        document.addEventListener('mousedown', handleClickOutside);
        return () => document.removeEventListener('mousedown', handleClickOutside);
    }, [onClose, anchorRef]);

    const renderHeader = () => (
        <div className="datepicker-header" style={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', marginBottom: '1rem', padding: '0 0.5rem' }}>
            <button onClick={() => setCurrentMonth(subMonths(currentMonth, 1))} style={{ padding: '0.25rem', background: 'none', border: 'none', cursor: 'pointer', color: 'var(--weekly-text-light, #9ca3af)', transition: 'color 0.2s' }}>
                <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round"><polyline points="15 18 9 12 15 6"></polyline></svg>
            </button>
            <div style={{ fontWeight: 'bold', fontSize: '0.875rem', letterSpacing: '0.05em', textTransform: 'uppercase', color: 'var(--weekly-text, #374151)' }}>
                {format(currentMonth, 'MMMM yyyy', { locale })}
            </div>
            <button onClick={() => setCurrentMonth(addMonths(currentMonth, 1))} style={{ padding: '0.25rem', background: 'none', border: 'none', cursor: 'pointer', color: 'var(--weekly-text-light, #9ca3af)', transition: 'color 0.2s' }}>
                <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round"><polyline points="9 18 15 12 9 6"></polyline></svg>
            </button>
        </div>
    );

    const renderDays = () => {
        const days = [];
        const startDate = startOfWeek(currentMonth, { weekStartsOn: 1 });
        for (let i = 0; i < 7; i++) {
            days.push(
                <div key={i} style={{ textAlign: 'center', fontSize: '0.75rem', fontWeight: 'bold', color: 'var(--weekly-text-light, #9ca3af)', padding: '0.5rem 0' }}>
                    {format(addDays(startDate, i), 'EEEEEE', { locale })}
                </div>
            );
        }
        return <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', marginBottom: '0.5rem' }}>{days}</div>;
    };

    const renderCells = () => {
        const monthStart = startOfMonth(currentMonth);
        const monthEnd = endOfMonth(monthStart);
        const startDate = startOfWeek(monthStart, { weekStartsOn: 1 });
        const endDate = endOfWeek(monthEnd, { weekStartsOn: 1 });

        const cells = [];
        let day = startDate;

        while (day <= endDate) {
            const row = [];
            for (let i = 0; i < 7; i++) {
                const cloneDay = day;
                const isSelected = isSameDay(day, selected);
                const isToday = isSameDay(day, new Date());
                const isCurrentMonth = isSameMonth(day, monthStart);
                const isDaySelected = isSelected;

                row.push(
                    <div
                        key={day.toString()}
                        onClick={() => {
                            onSelect(cloneDay);
                            onClose();
                        }}
                        style={{
                            height: '2rem',
                            width: '2rem',
                            display: 'flex',
                            alignItems: 'center',
                            justifyContent: 'center',
                            fontSize: '0.875rem',
                            borderRadius: '50%',
                            cursor: 'pointer',
                            transition: 'all 0.2s',
                            margin: '0 auto',
                            color: !isCurrentMonth ? 'var(--weekly-text-light, #d1d5db)' : isDaySelected ? 'white' : 'var(--weekly-text, #374151)',
                            background: isDaySelected ? 'black' : 'transparent',
                            fontWeight: isDaySelected ? 'bold' : 'normal',
                            boxShadow: isDaySelected ? '0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06)' : 'none',
                            transform: isDaySelected ? 'scale(1.1)' : 'none',
                            ...(isToday && !isDaySelected ? { color: '#ef4444', fontWeight: 'bold' } : {})
                        }}
                        onMouseEnter={(e) => {
                            if (!isDaySelected) e.currentTarget.style.backgroundColor = 'var(--weekly-hover-bg, #f3f4f6)';
                        }}
                        onMouseLeave={(e) => {
                            if (!isDaySelected) e.currentTarget.style.backgroundColor = 'transparent';
                        }}
                    >
                        {format(day, 'd')}
                    </div>
                );
                day = addDays(day, 1);
            }
            cells.push(row);
        }

        return (
            <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', gap: '0.5rem 0' }}>
                {cells.flat()}
            </div>
        );
    };

    // Use fixed positioning via portal if we have an anchor, otherwise fallback to absolute
    const usePortal = !!anchorRef?.current && !!position;

    const pickerContent = (
        <div ref={modalRef} style={{
            position: usePortal ? 'fixed' : 'absolute',
            top: usePortal ? position!.top : '100%',
            left: usePortal ? position!.left : '50%',
            transform: usePortal ? 'none' : 'translateX(-50%)',
            marginTop: usePortal ? 0 : '0.5rem',
            backgroundColor: 'var(--weekly-bg, white)',
            borderRadius: '0.5rem',
            boxShadow: '0 20px 25px -5px rgba(0, 0, 0, 0.15), 0 10px 10px -5px rgba(0, 0, 0, 0.08)',
            padding: '1rem',
            zIndex: 9999,
            width: '18rem',
            border: '1px solid var(--weekly-border, #e5e7eb)',
            animation: 'simpleDatePickerFadeIn 0.15s ease-out'
        }}>
            {renderHeader()}
            {renderDays()}
            {renderCells()}
            <style>{`
                @keyframes simpleDatePickerFadeIn {
                    from { opacity: 0; transform: translateY(-5px); }
                    to { opacity: 1; transform: translateY(0); }
                }
            `}</style>
        </div>
    );

    if (usePortal) {
        return createPortal(pickerContent, document.body);
    }

    return pickerContent;
}