import { useEffect, useState } from 'react';

import { readUrlState, writeUrlState } from '../../admin/js/url-state.js';
import { trackUxEvent } from '../../telemetry.js';
import { logoutAndRedirect } from '../shared/auth-client.js';
import { SESSION_PHASES } from '../shared/session-policy.js';
import { useAuthorizedSession } from '../shared/use-authorized-session.js';
import { AsyncCombobox } from '../shared/ui/AsyncCombobox.jsx';
import { AsyncState } from '../shared/ui/AsyncState.jsx';
import { buildScheduleOverviewModel } from '../../schedule-overview.js';
import { ScheduleOverview } from '../shared/ui/ScheduleOverview.jsx';
import { WeekGrid } from './WeekGrid.jsx';
import {
    addDays,
    buildWeekStatusMessage,
    fetchGroupOptions,
    fetchSchedule,
    formatWeekLabel,
    groupOptionDescription,
    GROUP_STORAGE_KEY,
    OVERVIEW_DAYS,
    parseIsoDate,
    resolveSelectedGroup,
    startOfWeek,
    toIsoDate,
    weekEndIso
} from './student-service.js';

const THEME_STORAGE_KEY = 'theme';

export function StudentApp() {
    const sessionState = useAuthorizedSession(['STUDENT']);

    useEffect(() => {
        document.documentElement.dataset.theme = localStorage.getItem(THEME_STORAGE_KEY) || 'light';
    }, []);

    if (sessionState.phase === SESSION_PHASES.loading) {
        return (
            <main className="shell">
                <AsyncState kind="loading" title="Расписание студента" message="Проверяем сессию…" />
            </main>
        );
    }

    if (sessionState.phase !== SESSION_PHASES.ready) {
        return (
            <main className="shell">
                <AsyncState kind="error" title="Раздел недоступен" message={sessionState.message} />
            </main>
        );
    }

    return <StudentWorkspace />;
}

function StudentWorkspace() {
    const [initialUrlState] = useState(() => readUrlState({ studentGroup: '', studentDate: '' }));
    const [weekStart, setWeekStart] = useState(() => startOfWeek(
        initialUrlState.studentDate ? parseIsoDate(initialUrlState.studentDate) : new Date()
    ));
    const [group, setGroup] = useState(null);
    const [groupsState, setGroupsState] = useState({ kind: 'loading' });
    const [groupsReload, setGroupsReload] = useState(0);
    const [scheduleState, setScheduleState] = useState({ kind: 'loading' });
    const [overviewState, setOverviewState] = useState({ kind: 'loading' });
    const [overviewReload, setOverviewReload] = useState(0);

    const weekStartIso = toIsoDate(weekStart);
    const groupId = group ? String(group.id) : '';

    useEffect(() => {
        let active = true;
        (async () => {
            setGroupsState({ kind: 'loading' });
            const savedGroupId = initialUrlState.studentGroup
                || localStorage.getItem(GROUP_STORAGE_KEY)
                || '';
            try {
                const groups = await fetchGroupOptions({ selectedId: savedGroupId });
                if (!active) return;
                if (!groups.length) {
                    setGroupsState({ kind: 'empty' });
                    setOverviewState({ kind: 'empty', message: 'Нет доступных групп' });
                    return;
                }
                const selected = resolveSelectedGroup(groups, savedGroupId);
                applyGroup(selected);
                setGroupsState({ kind: 'ready' });
            } catch {
                if (!active) return;
                setGroupsState({ kind: 'error' });
                setOverviewState({ kind: 'error', message: 'Не удалось загрузить ближайшие занятия' });
            }
        })();
        return () => {
            active = false;
        };
    }, [groupsReload, initialUrlState]);

    useEffect(() => {
        writeUrlState({ studentDate: weekStartIso });
    }, [weekStartIso]);

    useEffect(() => {
        if (!group) return undefined;
        let active = true;
        (async () => {
            setScheduleState({ kind: 'loading' });
            try {
                const lessons = await fetchSchedule({
                    groupId: String(group.id),
                    startDate: weekStartIso,
                    endDate: weekEndIso(weekStart)
                });
                if (!active) return;
                setScheduleState({ kind: 'ready', lessons });
                trackUxEvent('student_schedule_loaded', {
                    lessons: lessons.length,
                    startDate: weekStartIso,
                    groupId: String(group.id)
                });
            } catch {
                if (!active) return;
                setScheduleState({ kind: 'error' });
            }
        })();
        return () => {
            active = false;
        };
    }, [group, weekStart, weekStartIso]);

    useEffect(() => {
        if (!group) return undefined;
        let active = true;
        (async () => {
            setOverviewState({ kind: 'loading' });
            const now = new Date();
            try {
                const lessons = await fetchSchedule({
                    groupId: String(group.id),
                    startDate: toIsoDate(now),
                    endDate: toIsoDate(addDays(now, OVERVIEW_DAYS))
                });
                if (!active) return;
                setOverviewState({ kind: 'ready', lessons, now });
                const overview = buildScheduleOverviewModel(lessons, now);
                trackUxEvent('student_schedule_overview_loaded', {
                    todayCount: overview.todayLessons.length,
                    hasNext: Boolean(overview.nextLesson),
                    groupId: String(group.id)
                });
            } catch {
                if (!active) return;
                setOverviewState({ kind: 'error', message: 'Не удалось загрузить ближайшие занятия' });
            }
        })();
        return () => {
            active = false;
        };
    }, [group, overviewReload]);

    function applyGroup(nextGroup) {
        setGroup(nextGroup);
        localStorage.setItem(GROUP_STORAGE_KEY, String(nextGroup.id));
        writeUrlState({ studentGroup: String(nextGroup.id) });
    }

    function handleGroupSelect(nextGroup) {
        if (!nextGroup) return;
        applyGroup(nextGroup);
        trackUxEvent('student_group_selected', { groupId: String(nextGroup.id) });
    }

    function moveWeek(delta) {
        setWeekStart(current => addDays(current, delta * 7));
    }

    function goToCurrentWeek() {
        setWeekStart(startOfWeek(new Date()));
    }

    function handleDateChange(event) {
        if (event.target.value) {
            setWeekStart(startOfWeek(parseIsoDate(event.target.value)));
        }
    }

    function toggleTheme() {
        const next = document.documentElement.dataset.theme === 'dark' ? 'light' : 'dark';
        document.documentElement.dataset.theme = next;
        localStorage.setItem(THEME_STORAGE_KEY, next);
    }

    function handleLogout(event) {
        event.preventDefault();
        void logoutAndRedirect();
    }

    return (
        <main className="shell">
            <header className="topbar">
                <div className="title">
                    <h1>Расписание студента</h1>
                    <span>{formatWeekLabel(weekStart)}</span>
                </div>
                <div className="actions">
                    <button
                        className="btn btn-icon-md btn-secondary"
                        type="button"
                        aria-label="Переключить тему"
                        onClick={toggleTheme}
                    >
                        <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
                            <path d="M21 12.79A9 9 0 1 1 11.21 3a7 7 0 0 0 9.79 9.79z" />
                        </svg>
                    </button>
                    <a className="btn btn-danger-subtle" href="/" onClick={handleLogout}>Выйти</a>
                </div>
            </header>

            <section className="toolbar">
                {groupsState.kind === 'ready' && group ? (
                    <AsyncCombobox
                        allowClear={false}
                        ariaLabel="Группа"
                        emptyLabel="Подходящие группы не найдены"
                        placeholder="Найдите группу по названию или специальности"
                        load={(query, selectedId) => fetchGroupOptions({ query, selectedId })}
                        onSelect={handleGroupSelect}
                        optionDescription={groupOptionDescription}
                        optionLabel={option => option.name}
                        optionValue={option => option.id}
                        selectedLabel={group.name}
                        selectedValue={groupId}
                    />
                ) : (
                    <select className="select" aria-label="Группа" disabled>
                        <option value="">{groupSelectPlaceholder(groupsState.kind)}</option>
                    </select>
                )}
                <div className="week-nav">
                    <button className="btn btn-icon-md btn-secondary" type="button" aria-label="Предыдущая неделя" onClick={() => moveWeek(-1)}>
                        <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
                            <polyline points="15 18 9 12 15 6" />
                        </svg>
                    </button>
                    <button className="btn btn-md btn-primary" type="button" onClick={goToCurrentWeek}>Сегодня</button>
                    <button className="btn btn-icon-md btn-secondary" type="button" aria-label="Следующая неделя" onClick={() => moveWeek(1)}>
                        <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
                            <polyline points="9 18 15 12 9 6" />
                        </svg>
                    </button>
                </div>
                <input
                    className="date-input"
                    type="date"
                    aria-label="Дата недели"
                    value={weekStartIso}
                    onChange={handleDateChange}
                />
            </section>

            {overviewState.kind === 'ready' ? (
                <ScheduleOverview
                    lessons={overviewState.lessons}
                    now={overviewState.now}
                    onGoToday={goToCurrentWeek}
                    role="student"
                />
            ) : (
                <section className="schedule-overview" aria-live="polite">
                    {overviewState.kind === 'empty' ? (
                        <AsyncState kind="empty" title="Быстрый обзор" message={overviewState.message || 'В ближайшие дни занятий нет'} />
                    ) : overviewState.kind === 'error' ? (
                        <AsyncState
                            kind="error"
                            title="Быстрый обзор"
                            message={overviewState.message || 'Не удалось загрузить ближайшие занятия'}
                            onRetry={() => setOverviewReload(reload => reload + 1)}
                        />
                    ) : (
                        <AsyncState kind="loading" title="Быстрый обзор" message="Загружаем ближайшие занятия…" />
                    )}
                </section>
            )}

            <div className={`status${scheduleState.kind === 'error' ? ' error' : ''}`}>
                {statusMessage(scheduleState, groupsState)}
            </div>

            {groupsState.kind === 'error' ? (
                <AsyncState
                    kind="error"
                    title="Группы"
                    message="Не удалось загрузить группы"
                    onRetry={() => setGroupsReload(reload => reload + 1)}
                />
            ) : scheduleState.kind === 'ready' ? (
                <WeekGrid weekStart={weekStart} lessons={scheduleState.lessons} />
            ) : scheduleState.kind === 'error' ? (
                <WeekGrid weekStart={weekStart} lessons={[]} emptyMessage="Ошибка загрузки" />
            ) : (
                <WeekGrid
                    weekStart={weekStart}
                    lessons={[]}
                    emptyMessage={groupId ? 'Загрузка...' : 'Нет выбранной группы'}
                />
            )}
        </main>
    );
}

function groupSelectPlaceholder(kind) {
    if (kind === 'empty') return 'Группы не найдены';
    if (kind === 'error') return 'Ошибка загрузки групп';
    return 'Загрузка групп...';
}

function statusMessage(scheduleState, groupsState) {
    if (groupsState.kind === 'error') return 'Не удалось загрузить группы';
    if (groupsState.kind === 'empty') return 'Выберите группу';
    if (scheduleState.kind === 'error') return 'Не удалось загрузить расписание';
    if (scheduleState.kind === 'ready') return buildWeekStatusMessage(scheduleState.lessons);
    return 'Загрузка расписания...';
}