import { useState, useMemo, useCallback } from 'react';
import { MIN_YEAR, WEEKDAYS, MONTH_NAMES } from '@/constants';
import { getTodayKST } from '@/utils';

/**
 * 캘린더 훅
 * 날짜 선택, 월 이동 등 캘린더 로직 제공
 * @param {Date|string} initialDate - 초기 날짜
 */
export function useCalendar(initialDate = new Date()) {
  // initialDate가 Date 객체가 아니면 변환
  const ensureDate = (date) => {
    if (date instanceof Date) return date;
    if (typeof date === 'string') return new Date(date);
    return new Date();
  };

  const [currentDate, setCurrentDate] = useState(() => ensureDate(initialDate));
  const [selectedDate, setSelectedDate] = useState(getTodayKST());

  const year = currentDate.getFullYear();
  const month = currentDate.getMonth();

  // 캘린더 데이터 계산
  const calendarData = useMemo(() => {
    const firstDay = new Date(year, month, 1).getDay();
    const daysInMonth = new Date(year, month + 1, 0).getDate();
    const prevMonthDays = new Date(year, month, 0).getDate();

    // 캘린더에 표시할 날짜 배열 생성
    const days = [];

    // 이전 달 날짜
    for (let i = firstDay - 1; i >= 0; i--) {
      days.push({
        day: prevMonthDays - i,
        isCurrentMonth: false,
        date: new Date(year, month - 1, prevMonthDays - i),
      });
    }

    // 현재 달 날짜
    for (let i = 1; i <= daysInMonth; i++) {
      days.push({
        day: i,
        isCurrentMonth: true,
        date: new Date(year, month, i),
      });
    }

    // 다음 달 날짜 (6주 채우기)
    const remaining = 42 - days.length; // 6주 * 7일 = 42
    for (let i = 1; i <= remaining; i++) {
      days.push({
        day: i,
        isCurrentMonth: false,
        date: new Date(year, month + 1, i),
      });
    }

    return {
      year,
      month,
      monthName: MONTH_NAMES[month],
      firstDay,
      daysInMonth,
      prevMonthDays,
      weekdays: WEEKDAYS,
      days,
    };
  }, [year, month]);

  // 이전 월로 이동 가능 여부
  const canGoPrevMonth = !(year === MIN_YEAR && month === 0);

  // 선택 날짜 업데이트 헬퍼
  const updateSelectedDate = useCallback((newDate) => {
    const today = new Date();
    if (
      newDate.getFullYear() === today.getFullYear() &&
      newDate.getMonth() === today.getMonth()
    ) {
      setSelectedDate(getTodayKST());
    } else {
      const firstDay = `${newDate.getFullYear()}-${String(newDate.getMonth() + 1).padStart(2, '0')}-01`;
      setSelectedDate(firstDay);
    }
  }, []);

  // 이전 월로 이동
  const goToPrevMonth = useCallback(() => {
    if (!canGoPrevMonth) return;
    const newDate = new Date(year, month - 1, 1);
    setCurrentDate(newDate);
    updateSelectedDate(newDate);
  }, [year, month, canGoPrevMonth, updateSelectedDate]);

  // 다음 월로 이동
  const goToNextMonth = useCallback(() => {
    const newDate = new Date(year, month + 1, 1);
    setCurrentDate(newDate);
    updateSelectedDate(newDate);
  }, [year, month, updateSelectedDate]);

  // 특정 월로 이동
  const goToMonth = useCallback(
    (newYear, newMonth) => {
      const newDate = new Date(newYear, newMonth, 1);
      setCurrentDate(newDate);
      updateSelectedDate(newDate);
    },
    [updateSelectedDate]
  );

  // 오늘로 이동
  const goToToday = useCallback(() => {
    const today = new Date();
    setCurrentDate(today);
    setSelectedDate(getTodayKST());
  }, []);

  // 날짜 선택
  const selectDate = useCallback(
    (day) => {
      const dateStr = `${year}-${String(month + 1).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
      setSelectedDate(dateStr);
    },
    [year, month]
  );

  return {
    ...calendarData,
    currentDate,
    selectedDate,
    canGoPrev: canGoPrevMonth,
    canGoPrevMonth,
    goToPrevMonth,
    goToNextMonth,
    goToMonth,
    goToToday,
    selectDate,
    setSelectedDate,
  };
}