import React, { useMemo, useState } from 'react';
import { Button, Segmented, Select } from 'antd';
import { PlusOutlined, GlobalOutlined, BranchesOutlined } from '@ant-design/icons';
import dayjs from 'dayjs';
import styles from './ActivityCalendar.less';

const weekDays = ['周日', '周一', '周二', '周三', '周四', '周五', '周六'];

const calendarEvents = [
    {
        id: 'earth-day',
        title: '世界环保日',
        start: dayjs('2020-12-14'),
        end: dayjs('2020-12-15'),
        tone: 'sand',
        icon: <GlobalOutlined />,
    },
    {
        id: 'tree-day',
        title: '全国植树日',
        start: dayjs('2020-12-24'),
        end: dayjs('2020-12-31'),
        tone: 'mint',
        icon: <BranchesOutlined />,
    },
];

const buildGrid = (referenceDate, viewMode) => {
    if (viewMode === 'week') {
        const startOfWeek = referenceDate.startOf('week');
        const days = Array.from({ length: 7 }, (_, index) => startOfWeek.add(index, 'day'));
        return { days, gridStart: startOfWeek, weeks: 1 };
    }

    const startOfMonth = referenceDate.startOf('month');
    const gridStart = startOfMonth.startOf('week');
    const days = Array.from({ length: 42 }, (_, index) => gridStart.add(index, 'day'));

    return { days, gridStart, weeks: 6 };
};

const buildEventSegments = (events, gridStart, weeks) => {
    const gridEnd = gridStart.add(weeks * 7 - 1, 'day').endOf('day');
    const segments = [];

    events.forEach((event) => {
        const start = event.start;
        const end = event.end;

        if (end.isBefore(gridStart) || start.isAfter(gridEnd)) {
            return;
        }

        for (let weekIndex = 0; weekIndex < weeks; weekIndex += 1) {
            const weekStart = gridStart.add(weekIndex * 7, 'day');
            const weekEnd = weekStart.add(6, 'day').endOf('day');

            const segmentStart = start.isAfter(weekStart) ? start : weekStart;
            const segmentEnd = end.isBefore(weekEnd) ? end : weekEnd;

            if (segmentEnd.isBefore(weekStart) || segmentStart.isAfter(weekEnd)) {
                continue;
            }

            const columnStart = segmentStart.diff(weekStart, 'day') + 1;
            const columnEnd = segmentEnd.diff(weekStart, 'day') + 2;

            segments.push({
                id: `${event.id}-${weekIndex}`,
                title: event.title,
                tone: event.tone,
                icon: event.icon,
                rowStart: weekIndex + 1,
                rowEnd: weekIndex + 2,
                columnStart,
                columnEnd,
            });
        }
    });

    return segments;
};

const ActivityCalendar = () => {
    const [currentDate, setCurrentDate] = useState(dayjs('2020-12-01'));
    const [viewMode, setViewMode] = useState('month');

    const { days, gridStart, weeks } = useMemo(() => buildGrid(currentDate, viewMode), [currentDate, viewMode]);
    const segments = useMemo(() => buildEventSegments(calendarEvents, gridStart, weeks), [gridStart, weeks]);

    const yearOptions = useMemo(() => {
        const baseYear = dayjs().year();
        const startYear = Math.min(2020, baseYear - 4);
        return Array.from({ length: 10 }, (_, index) => startYear + index);
    }, []);

    const handleYearChange = (year) => {
        setCurrentDate((prev) => prev.year(year));
    };

    const handleMonthChange = (month) => {
        setCurrentDate((prev) => prev.month(month - 1));
    };

    const handleViewChange = (mode) => {
        setViewMode(mode);
    };

    const handleBackToToday = () => {
        const today = dayjs();
        setCurrentDate(today);
        setViewMode('month');
    };

    return (
        <div className={styles.container}>
            <div className={styles.toolbar}>
                <Button type="primary" icon={<PlusOutlined />} className={styles.createButton}>
                    新建活动
                </Button>
                <div className={styles.toolbarRight}>
                    <Select
                        size="middle"
                        value={currentDate.year()}
                        className={styles.select}
                        popupClassName={styles.dropdown}
                        onChange={handleYearChange}
                        options={yearOptions.map((year) => ({ value: year, label: `${year}` }))}
                    />
                    <Select
                        size="middle"
                        value={currentDate.month() + 1}
                        className={styles.select}
                        popupClassName={styles.dropdown}
                        onChange={handleMonthChange}
                        options={Array.from({ length: 12 }, (_, index) => ({
                            value: index + 1,
                            label: `${index + 1}月`,
                        }))}
                    />
                    <Segmented
                        value={viewMode}
                        onChange={handleViewChange}
                        options={[
                            { label: '月', value: 'month' },
                            { label: '周', value: 'week' },
                        ]}
                        className={styles.segmented}
                    />
                    <Button className={styles.dayButton} onClick={handleBackToToday}>
                        日
                    </Button>
                </div>
            </div>

            <div className={styles.calendarWrapper}>
                <div className={styles.weekHeader}>
                    {weekDays.map((day) => (
                        <div key={day} className={styles.weekCell}>
                            {day}
                        </div>
                    ))}
                </div>

                <div className={styles.calendarGrid}>
                    {days.map((day) => {
                        const isCurrentMonth = day.month() === currentDate.month();
                        return (
                            <div
                                key={day.format('YYYY-MM-DD')}
                                className={`${styles.dayCell} ${isCurrentMonth ? '' : styles.dimmed}`}
                            >
                                <span className={styles.dayNumber}>{day.date()}</span>
                            </div>
                        );
                    })}

                    {segments.map((segment) => (
                        <div
                            key={segment.id}
                            className={`${styles.eventBlock} ${styles[segment.tone]}`}
                            style={{
                                gridColumnStart: segment.columnStart,
                                gridColumnEnd: segment.columnEnd,
                                gridRowStart: segment.rowStart,
                                gridRowEnd: segment.rowEnd,
                            }}
                        >
                            <div className={styles.eventInfo}>
                                <span className={styles.eventDot} />
                                <span className={styles.eventTitle}>{segment.title}</span>
                            </div>
                            <div className={styles.eventIcon}>{segment.icon}</div>
                        </div>
                    ))}
                </div>
            </div>
        </div>
    );
};

export default ActivityCalendar;