"use client";

/**
 * Calendar - 课案日历组件
 *
 * 维护者：ai13（teacher-portal）
 * 关联：lesson-plans/calendar 页面复用
 *
 * 特性：
 * - 月视图，支持前后月切换
 * - 日期点击回调
 * - 日期标记（有课案的日期高亮）
 * - 纯 CSS + var(--*) 设计令牌
 */

import { useState, useMemo, useCallback } from "react";

export interface CalendarEvent {
  date: string; // ISO date string YYYY-MM-DD
  title: string;
  type?: "lesson" | "exam" | "meeting";
}

export interface CalendarProps {
  /** 初始月份（默认当前月） */
  initialDate?: Date;
  /** 事件列表 */
  events?: CalendarEvent[];
  /** 日期点击回调 */
  onDateClick?: (date: Date) => void;
  /** 月份切换回调 */
  onMonthChange?: (date: Date) => void;
}

const WEEKDAYS = ["日", "一", "二", "三", "四", "五", "六"];
const WEEKDAYS_EN = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];

function formatDate(date: Date): string {
  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}`;
}

function getEventColor(type: CalendarEvent["type"]): string {
  switch (type) {
    case "exam":
      return "var(--color-danger)";
    case "meeting":
      return "var(--color-warning)";
    case "lesson":
    default:
      return "var(--color-accent)";
  }
}

export function Calendar({
  initialDate = new Date(),
  events = [],
  onDateClick,
  onMonthChange,
}: CalendarProps): React.ReactElement {
  const [currentDate, setCurrentDate] = useState(initialDate);

  const eventsByDate = useMemo(() => {
    const map = new Map<string, CalendarEvent[]>();
    for (const evt of events) {
      const existing = map.get(evt.date) || [];
      existing.push(evt);
      map.set(evt.date, existing);
    }
    return map;
  }, [events]);

  const days = useMemo(() => {
    const year = currentDate.getFullYear();
    const month = currentDate.getMonth();
    const firstDay = new Date(year, month, 1);
    const lastDay = new Date(year, month + 1, 0);
    const startWeekday = firstDay.getDay();
    const daysInMonth = lastDay.getDate();

    const cells: Array<{ date: Date | null; isCurrentMonth: boolean }> = [];

    // 上月填充
    for (let i = 0; i < startWeekday; i++) {
      cells.push({ date: null, isCurrentMonth: false });
    }

    // 当月
    for (let d = 1; d <= daysInMonth; d++) {
      cells.push({ date: new Date(year, month, d), isCurrentMonth: true });
    }

    // 下月填充（补齐 6 行 = 42 格）
    while (cells.length < 42) {
      cells.push({ date: null, isCurrentMonth: false });
    }

    return cells;
  }, [currentDate]);

  const handlePrevMonth = useCallback(() => {
    const prev = new Date(
      currentDate.getFullYear(),
      currentDate.getMonth() - 1,
      1,
    );
    setCurrentDate(prev);
    onMonthChange?.(prev);
  }, [currentDate, onMonthChange]);

  const handleNextMonth = useCallback(() => {
    const next = new Date(
      currentDate.getFullYear(),
      currentDate.getMonth() + 1,
      1,
    );
    setCurrentDate(next);
    onMonthChange?.(next);
  }, [currentDate, onMonthChange]);

  const today = formatDate(new Date());

  return (
    <div className="w-full rounded-xl border bg-card p-4">
      {/* 月份导航 */}
      <div className="flex items-center justify-between mb-4">
        <button
          type="button"
          onClick={handlePrevMonth}
          className="px-3 py-1 text-sm transition-opacity hover:opacity-70"
          style={{
            color: "var(--color-ink-muted)",
            borderRadius: "var(--radius-button)",
          }}
          aria-label="上一月"
        >
          ←
        </button>
        <h3
          className="text-base font-medium"
          style={{
            color: "var(--color-ink)",
            fontFamily: "var(--font-family-serif)",
          }}
        >
          {currentDate.getFullYear()} 年 {currentDate.getMonth() + 1} 月
        </h3>
        <button
          type="button"
          onClick={handleNextMonth}
          className="px-3 py-1 text-sm transition-opacity hover:opacity-70"
          style={{
            color: "var(--color-ink-muted)",
            borderRadius: "var(--radius-button)",
          }}
          aria-label="下一月"
        >
          →
        </button>
      </div>

      {/* 星期表头 */}
      <div className="grid grid-cols-7 gap-1 mb-2">
        {WEEKDAYS.map((day, i) => (
          <div
            key={`wd-${i}`}
            className="text-center text-xs uppercase tracking-wide py-2"
            style={{ color: "var(--color-ink-subtle)" }}
          >
            {day}
          </div>
        ))}
      </div>

      {/* 日期网格 */}
      <div className="grid grid-cols-7 gap-1">
        {days.map((cell, i) => {
          if (!cell.date) {
            return <div key={`empty-${i}`} className="min-h-[60px]" />;
          }

          const dateStr = formatDate(cell.date);
          const dayEvents = eventsByDate.get(dateStr) || [];
          const isToday = dateStr === today;

          return (
            <button
              type="button"
              key={`day-${dateStr}`}
              onClick={() => onDateClick?.(cell.date!)}
              className="min-h-[60px] p-1 text-left transition-colors hover:bg-muted"
              style={{
                background: isToday
                  ? "hsl(var(--primary) / 0.1)"
                  : "transparent",
                borderRadius: "var(--radius)",
                border: isToday
                  ? "1px solid hsl(var(--primary))"
                  : "1px solid transparent",
                cursor: "pointer",
              }}
            >
              <div
                className="text-xs mb-1"
                style={{
                  color: isToday
                    ? "hsl(var(--primary))"
                    : "hsl(var(--muted-foreground))",
                  fontWeight: isToday ? "600" : "400",
                }}
              >
                {cell.date.getDate()}
              </div>
              {/* 事件标记 */}
              <div className="space-y-0.5">
                {dayEvents.slice(0, 2).map((evt, j) => (
                  <div
                    key={`evt-${j}`}
                    className="text-[10px] truncate px-1 py-0.5"
                    style={{
                      background: getEventColor(evt.type),
                      color: "var(--color-ink-on-accent)",
                      borderRadius: "2px",
                    }}
                    title={evt.title}
                  >
                    {evt.title}
                  </div>
                ))}
                {dayEvents.length > 2 && (
                  <div
                    className="text-[10px]"
                    style={{ color: "var(--color-ink-subtle)" }}
                  >
                    +{dayEvents.length - 2} 更多
                  </div>
                )}
              </div>
            </button>
          );
        })}
      </div>
    </div>
  );
}

export { WEEKDAYS, WEEKDAYS_EN, formatDate };

export default Calendar;