import React, { useState, useEffect } from 'react';
import { ChevronLeft, ChevronRight } from 'lucide-react';

const API_BASE = process.env.REACT_APP_API_BASE || 'http://localhost:3001/api';

const MONTH_NAMES = [
    'January', 'February', 'March', 'April', 'May', 'June',
    'July', 'August', 'September', 'October', 'November', 'December'
];
const DAY_NAMES = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'];

function toLocalDateStr(date) {
    const y = date.getFullYear();
    const m = String(date.getMonth() + 1).padStart(2, '0');
    const d = String(date.getDate()).padStart(2, '0');
    return `${y}-${m}-${d}`;
}

export default function CalendarWidget() {
    const today    = new Date();
    const todayStr = toLocalDateStr(today);

    const [calYear,  setCalYear]  = useState(today.getFullYear());
    const [calMonth, setCalMonth] = useState(today.getMonth()); // 0-indexed

    // Map of "YYYY-MM-DD" → count of findings due that day
    const [dueDates, setDueDates] = useState({});

    useEffect(() => {
        fetch(`${API_BASE}/ivanti/findings`, { credentials: 'include' })
            .then((r) => (r.ok ? r.json() : null))
            .then((data) => {
                if (!data?.findings) return;
                const counts = {};
                data.findings.forEach((f) => {
                    if (f.dueDate) {
                        counts[f.dueDate] = (counts[f.dueDate] || 0) + 1;
                    }
                });
                setDueDates(counts);
            })
            .catch(() => {});
    }, []);

    const prevMonth = () => {
        if (calMonth === 0) { setCalMonth(11); setCalYear((y) => y - 1); }
        else { setCalMonth((m) => m - 1); }
    };

    const nextMonth = () => {
        if (calMonth === 11) { setCalMonth(0); setCalYear((y) => y + 1); }
        else { setCalMonth((m) => m + 1); }
    };

    // Build cell array: null = padding, number = day of month
    const firstDow    = new Date(calYear, calMonth, 1).getDay(); // 0=Sun
    const daysInMonth = new Date(calYear, calMonth + 1, 0).getDate();
    const cells = [
        ...Array(firstDow).fill(null),
        ...Array.from({ length: daysInMonth }, (_, i) => i + 1),
    ];
    while (cells.length % 7 !== 0) cells.push(null); // complete last row

    const hasDueDatesThisMonth = cells.some((day) => {
        if (!day) return false;
        const ds = `${calYear}-${String(calMonth + 1).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
        return !!dueDates[ds];
    });

    return (
        <div>
            {/* Month navigation */}
            <div style={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', marginBottom: '0.75rem' }}>
                <button
                    onClick={prevMonth}
                    style={{ background: 'none', border: 'none', cursor: 'pointer', color: '#64748B', padding: '2px 4px', borderRadius: '4px', lineHeight: 1, transition: 'color 0.15s' }}
                    onMouseEnter={(e) => { e.currentTarget.style.color = '#0EA5E9'; }}
                    onMouseLeave={(e) => { e.currentTarget.style.color = '#64748B'; }}
                >
                    <ChevronLeft style={{ width: '14px', height: '14px' }} />
                </button>

                <span style={{ color: '#E2E8F0', fontFamily: 'monospace', fontWeight: '600', fontSize: '0.85rem' }}>
                    {MONTH_NAMES[calMonth]} {calYear}
                </span>

                <button
                    onClick={nextMonth}
                    style={{ background: 'none', border: 'none', cursor: 'pointer', color: '#64748B', padding: '2px 4px', borderRadius: '4px', lineHeight: 1, transition: 'color 0.15s' }}
                    onMouseEnter={(e) => { e.currentTarget.style.color = '#0EA5E9'; }}
                    onMouseLeave={(e) => { e.currentTarget.style.color = '#64748B'; }}
                >
                    <ChevronRight style={{ width: '14px', height: '14px' }} />
                </button>
            </div>

            {/* Day-of-week headers */}
            <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', gap: '2px', textAlign: 'center', marginBottom: '4px' }}>
                {DAY_NAMES.map((d) => (
                    <div key={d} style={{ fontSize: '0.6rem', color: '#475569', fontFamily: 'monospace', fontWeight: '600', textTransform: 'uppercase' }}>
                        {d}
                    </div>
                ))}
            </div>

            {/* Day cells */}
            <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', gap: '2px' }}>
                {cells.map((day, idx) => {
                    if (!day) return <div key={idx} />;

                    const dateStr  = `${calYear}-${String(calMonth + 1).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
                    const isToday  = dateStr === todayStr;
                    const dueCount = dueDates[dateStr] || 0;
                    const hasDue   = dueCount > 0;

                    return (
                        <div
                            key={idx}
                            title={hasDue ? `${dueCount} finding${dueCount > 1 ? 's' : ''} due` : undefined}
                            style={{
                                display: 'flex', flexDirection: 'column', alignItems: 'center',
                                gap: '2px', padding: '3px 1px',
                                borderRadius: '4px',
                                background: isToday ? 'rgba(14,165,233,0.2)' : 'transparent',
                                border: isToday ? '1px solid rgba(14,165,233,0.5)' : '1px solid transparent',
                                cursor: hasDue ? 'default' : 'default',
                            }}
                        >
                            <span style={{
                                fontSize: '0.7rem', fontFamily: 'monospace', lineHeight: 1,
                                color: isToday ? '#0EA5E9' : hasDue ? '#EF4444' : '#CBD5E1',
                                fontWeight: (isToday || hasDue) ? '700' : '400',
                            }}>
                                {day}
                            </span>
                            {/* Red dot indicator for due dates */}
                            {hasDue ? (
                                <div style={{
                                    width: '4px', height: '4px', borderRadius: '50%',
                                    background: '#EF4444',
                                    boxShadow: '0 0 4px rgba(239,68,68,0.6)',
                                    flexShrink: 0,
                                }} />
                            ) : (
                                <div style={{ width: '4px', height: '4px' }} /> // spacer to keep rows even
                            )}
                        </div>
                    );
                })}
            </div>

            {/* Legend — only shown when there are due dates this month */}
            {hasDueDatesThisMonth && (
                <div style={{ marginTop: '0.75rem', paddingTop: '0.625rem', borderTop: '1px solid rgba(255,255,255,0.05)', display: 'flex', alignItems: 'center', gap: '0.375rem' }}>
                    <div style={{ width: '6px', height: '6px', borderRadius: '50%', background: '#EF4444', boxShadow: '0 0 4px rgba(239,68,68,0.5)', flexShrink: 0 }} />
                    <span style={{ fontSize: '0.62rem', color: '#64748B', fontFamily: 'monospace', textTransform: 'uppercase', letterSpacing: '0.05em' }}>
                        Ivanti finding due
                    </span>
                </div>
            )}
        </div>
    );
}