import { useEffect, useState } from 'react';

import { dayName, formatDate, toIsoDate, weekDates } from '../shared/dates.js';
import {
    buildDesktopWeekModel,
    buildTeacherLessonChips,
    canRequestChange,
    lessonsByDate
} from './teacher-service.js';

const MOBILE_BREAKPOINT = '(max-width: 980px)';

export function TeacherWeekGrid({ emptyMessage = 'Загрузка...', lessons = [], onRequestLesson, weekStart }) {
    const mobile = useMobileLayout();

    if (mobile) {
        return <MobileWeek emptyMessage={emptyMessage} lessons={lessons} onRequestLesson={onRequestLesson} weekStart={weekStart} />;
    }
    return <DesktopWeek emptyMessage={emptyMessage} lessons={lessons} onRequestLesson={onRequestLesson} weekStart={weekStart} />;
}

function DesktopWeek({ emptyMessage, lessons, onRequestLesson, weekStart }) {
    const { days, slots, lessonsByKey } = buildDesktopWeekModel(weekStart, lessons);
    const hasLessons = lessons.length > 0;

    return (
        <section className="schedule" aria-live="polite">
            <div className="corner" />
            {days.map(day => <DayHead key={day.isoDate} date={day.date} />)}
            {hasLessons ? (
                slots.map(slot => (
                    <SlotRow
                        key={slot.order}
                        days={days}
                        lessonsByKey={lessonsByKey}
                        onRequestLesson={onRequestLesson}
                        slot={slot}
                    />
                ))
            ) : (
                <>
                    <div className="time-cell">Неделя</div>
                    {days.map(day => (
                        <div key={day.isoDate} className="day-cell">
                            <div className="empty">{emptyMessage}</div>
                        </div>
                    ))}
                </>
            )}
        </section>
    );
}

function SlotRow({ days, lessonsByKey, onRequestLesson, slot }) {
    return (
        <>
            <div className="time-cell">{slot.label}</div>
            {days.map(day => {
                const lesson = lessonsByKey.get(`${day.isoDate}:${slot.order}`);
                return (
                    <div key={`${day.isoDate}:${slot.order}`} className="day-cell">
                        {lesson
                            ? <LessonCard lesson={lesson} onRequestLesson={onRequestLesson} />
                            : <div className="empty">Нет занятия</div>}
                    </div>
                );
            })}
        </>
    );
}

function MobileWeek({ emptyMessage, lessons, onRequestLesson, weekStart }) {
    const byDate = lessonsByDate(lessons);

    return (
        <section className="schedule" aria-live="polite">
            {weekDates(weekStart).map(date => {
                const isoDate = toIsoDate(date);
                const dayLessons = byDate.get(isoDate) || [];
                return (
                    <article key={isoDate} className="mobile-day">
                        <DayHead date={date} />
                        <div className="mobile-list">
                            {dayLessons.length > 0
                                ? dayLessons.map((lesson, index) => (
                                    <LessonCard
                                        key={`${lesson.date}-${trimKey(lesson)}-${index}`}
                                        lesson={lesson}
                                        onRequestLesson={onRequestLesson}
                                    />
                                ))
                                : <div className="empty">{emptyMessage}</div>}
                        </div>
                    </article>
                );
            })}
        </section>
    );
}

function DayHead({ date }) {
    return (
        <div className="day-head">
            <strong>{dayName(date)}</strong>
            <span>{formatDate(date)}</span>
        </div>
    );
}

function LessonCard({ lesson, onRequestLesson }) {
    return (
        <div className="lesson">
            <div className="lesson-title">{lesson.subjectName}</div>
            <div className="lesson-meta">
                {buildTeacherLessonChips(lesson).map((chip, index) => (
                    <span key={index} className="chip">{chip}</span>
                ))}
            </div>
            {canRequestChange(lesson) ? (
                <button
                    className="btn btn-sm btn-secondary lesson-request-button"
                    type="button"
                    onClick={() => onRequestLesson(lesson)}
                >
                    Запросить изменение
                </button>
            ) : (
                <span className="lesson-change-note">Занятие уже изменено учебным отделом</span>
            )}
        </div>
    );
}

function trimKey(lesson) {
    return String(lesson.startTime || '').slice(0, 5);
}

function useMobileLayout() {
    const [mobile, setMobile] = useState(() => matchesMobile());

    useEffect(() => {
        if (typeof window === 'undefined' || !window.matchMedia) return undefined;
        const query = window.matchMedia(MOBILE_BREAKPOINT);
        const update = () => setMobile(query.matches);
        update();
        query.addEventListener('change', update);
        return () => query.removeEventListener('change', update);
    }, []);

    return mobile;
}

function matchesMobile() {
    return typeof window !== 'undefined' && Boolean(window.matchMedia)
        && window.matchMedia(MOBILE_BREAKPOINT).matches;
}