import { useState, useRef, useEffect } from 'react';
import styles from './DatePicker.module.css';

interface DatePickerProps {
  value: string; // 'YYYY-MM-DD' or ''
  onChange: (value: string) => void;
  placeholder?: string;
}

export function DatePicker({ value, onChange, placeholder = '选择日期' }: DatePickerProps) {
  const [open, setOpen] = useState(false);
  const wrapperRef = useRef<HTMLDivElement>(null);

  const today = new Date();
  const selected = value ? new Date(value + 'T00:00:00') : null;
  const [viewYear, setViewYear] = useState(selected?.getFullYear() ?? today.getFullYear());
  const [viewMonth, setViewMonth] = useState(selected?.getMonth() ?? today.getMonth());

  // Close on outside click
  useEffect(() => {
    if (!open) return;
    const handle = (e: MouseEvent) => {
      if (wrapperRef.current && !wrapperRef.current.contains(e.target as Node)) {
        setOpen(false);
      }
    };
    document.addEventListener('mousedown', handle);
    return () => document.removeEventListener('mousedown', handle);
  }, [open]);

  const prevMonth = () => {
    if (viewMonth === 0) { setViewMonth(11); setViewYear(viewYear - 1); }
    else setViewMonth(viewMonth - 1);
  };
  const nextMonth = () => {
    if (viewMonth === 11) { setViewMonth(0); setViewYear(viewYear + 1); }
    else setViewMonth(viewMonth + 1);
  };

  // Build calendar grid
  const firstDay = new Date(viewYear, viewMonth, 1).getDay(); // 0=Sun
  const daysInMonth = new Date(viewYear, viewMonth + 1, 0).getDate();
  const daysInPrevMonth = new Date(viewYear, viewMonth, 0).getDate();

  const cells: { day: number; month: number; year: number; isOther: boolean }[] = [];

  // Previous month padding
  for (let i = firstDay - 1; i >= 0; i--) {
    const m = viewMonth === 0 ? 11 : viewMonth - 1;
    const y = viewMonth === 0 ? viewYear - 1 : viewYear;
    cells.push({ day: daysInPrevMonth - i, month: m, year: y, isOther: true });
  }
  // Current month
  for (let d = 1; d <= daysInMonth; d++) {
    cells.push({ day: d, month: viewMonth, year: viewYear, isOther: false });
  }
  // Next month padding
  const remaining = 42 - cells.length;
  for (let d = 1; d <= remaining; d++) {
    const m = viewMonth === 11 ? 0 : viewMonth + 1;
    const y = viewMonth === 11 ? viewYear + 1 : viewYear;
    cells.push({ day: d, month: m, year: y, isOther: true });
  }

  const fmt = (y: number, m: number, d: number) =>
    `${y}-${String(m + 1).padStart(2, '0')}-${String(d).padStart(2, '0')}`;

  const todayStr = fmt(today.getFullYear(), today.getMonth(), today.getDate());
  const weekDays = ['日', '一', '二', '三', '四', '五', '六'];
  const monthNames = ['1月', '2月', '3月', '4月', '5月', '6月', '7月', '8月', '9月', '10月', '11月', '12月'];

  return (
    <div className={styles.wrapper} ref={wrapperRef}>
      <button
        type="button"
        className={styles.trigger}
        onClick={() => {
          if (!open && selected) {
            setViewYear(selected.getFullYear());
            setViewMonth(selected.getMonth());
          }
          setOpen(!open);
        }}
      >
        <svg className={styles.calendarIcon} width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
          <rect x="3" y="4" width="18" height="18" rx="2" />
          <path d="M16 2v4M8 2v4M3 10h18" />
        </svg>
        {value ? (
          <span>{value}</span>
        ) : (
          <span className={styles.placeholder}>{placeholder}</span>
        )}
        {value && (
          <button
            type="button"
            className={styles.clearBtn}
            onClick={(e) => { e.stopPropagation(); onChange(''); setOpen(false); }}
            title="清除"
          >
            <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
              <path d="M18 6L6 18M6 6l12 12" />
            </svg>
          </button>
        )}
      </button>

      {open && (
        <div className={styles.dropdown}>
          <div className={styles.header}>
            <button type="button" className={styles.navBtn} onClick={prevMonth}>&lt;</button>
            <span className={styles.monthLabel}>{viewYear}年 {monthNames[viewMonth]}</span>
            <button type="button" className={styles.navBtn} onClick={nextMonth}>&gt;</button>
          </div>
          <div className={styles.weekRow}>
            {weekDays.map((d) => <span key={d} className={styles.weekDay}>{d}</span>)}
          </div>
          <div className={styles.daysGrid}>
            {cells.map((c, i) => {
              const dateStr = fmt(c.year, c.month, c.day);
              const isToday = dateStr === todayStr;
              const isSelected = dateStr === value;
              return (
                <button
                  key={i}
                  type="button"
                  className={[
                    styles.dayCell,
                    c.isOther ? styles.otherMonth : '',
                    isToday ? styles.today : '',
                    isSelected ? styles.selected : '',
                  ].join(' ')}
                  onClick={() => {
                    onChange(dateStr);
                    setOpen(false);
                  }}
                >
                  {c.day}
                </button>
              );
            })}
          </div>
        </div>
      )}
    </div>
  );
}