import { useEffect, useState } from 'react';

import { readUrlState, writeUrlState } from '../../admin/js/url-state.js';
import { trackUxEvent } from '../../telemetry.js';
import { buildScheduleOverviewModel } from '../../schedule-overview.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 { AsyncState } from '../shared/ui/AsyncState.jsx';
import { ScheduleOverview } from '../shared/ui/ScheduleOverview.jsx';
import {
    addDays,
    formatWeekLabel,
    parseIsoDate,
    startOfWeek,
    toIsoDate,
    weekEndIso
} from '../shared/dates.js';
import { AbsencePanel } from './AbsencePanel.jsx';
import { PreferencesTab } from './PreferencesTab.jsx';
import { RequestDialog } from './RequestDialog.jsx';
import { RequestsTab } from './RequestsTab.jsx';
import { TeacherWeekGrid } from './TeacherWeekGrid.jsx';
import {
    cancelChangeRequest,
    createChangeRequest,
    fetchChangeRequests,
    fetchTeacherSchedule,
    pendingCount,
    WORKSPACE_TABS
} from './teacher-service.js';

const THEME_STORAGE_KEY = 'theme';
const OVERVIEW_DAYS = 14;

const TAB_TITLES = Object.freeze({
    preferences: 'Мои пожелания',
    requests: 'Заявки на изменение',
    schedule: 'Расписание'
});

export function TeacherApp() {
    const sessionState = useAuthorizedSession(['TEACHER']);

    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="Кабинет преподавателя" 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 <TeacherWorkspace teacherId={sessionState.session.userId} />;
}

function TeacherWorkspace({ teacherId }) {
    const [initialUrlState] = useState(() => readUrlState({ teacherTab: 'schedule', teacherDate: '' }));
    const [activeTab, setActiveTab] = useState(() => (
        WORKSPACE_TABS.includes(initialUrlState.teacherTab) ? initialUrlState.teacherTab : 'schedule'
    ));
    const [weekStart, setWeekStart] = useState(() => startOfWeek(
        initialUrlState.teacherDate ? parseIsoDate(initialUrlState.teacherDate) : new Date()
    ));
    const [scheduleState, setScheduleState] = useState({ kind: 'loading' });
    const [overviewState, setOverviewState] = useState({ kind: 'loading' });
    const [requestsState, setRequestsState] = useState({ kind: 'loading', items: [] });
    const [dialogLesson, setDialogLesson] = useState(null);

    const weekStartIso = toIsoDate(weekStart);

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

    useEffect(() => {
        let active = true;
        (async () => {
            setRequestsState({ kind: 'loading', items: [] });
            try {
                const items = await fetchChangeRequests();
                if (!active) return;
                setRequestsState({ kind: 'ready', items });
            } catch {
                if (!active) return;
                setRequestsState({ kind: 'error', items: [] });
            }
        })();
        return () => {
            active = false;
        };
    }, []);

    useEffect(() => {
        if (!teacherId) {
            setScheduleState({ kind: 'error', message: 'Не удалось определить преподавателя' });
            return undefined;
        }
        let active = true;
        (async () => {
            setScheduleState({ kind: 'loading' });
            try {
                const lessons = await fetchTeacherSchedule({
                    endDate: weekEndIso(weekStart),
                    startDate: weekStartIso,
                    teacherId
                });
                if (!active) return;
                setScheduleState({ kind: 'ready', lessons });
                trackUxEvent('teacher_schedule_loaded', { lessons: lessons.length, startDate: weekStartIso });
            } catch {
                if (!active) return;
                setScheduleState({ kind: 'error' });
            }
        })();
        return () => {
            active = false;
        };
    }, [teacherId, weekStart, weekStartIso]);

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

    function switchTab(name) {
        setActiveTab(name);
        writeUrlState({ teacherTab: name });
        trackUxEvent('teacher_workspace_opened', { section: name });
    }

    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();
    }

    async function refreshRequests() {
        try {
            const items = await fetchChangeRequests();
            setRequestsState({ kind: 'ready', items });
        } catch {
            setRequestsState({ kind: 'error', items: [] });
        }
    }

    async function handleCancelRequest(id) {
        try {
            await cancelChangeRequest(id);
            await refreshRequests();
        } catch {
            setRequestsState({ kind: 'error', items: [] });
        }
    }

    async function handleSubmitRequest(payload) {
        try {
            await createChangeRequest(payload);
            setDialogLesson(null);
            await refreshRequests();
            switchTab('requests');
        } catch {
            return false;
        }
        return true;
    }

    return (
        <main className="shell">
            <header className="topbar">
                <div className="title">
                    <h1>Кабинет преподавателя</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>

            <nav className="workspace-nav" aria-label="Разделы кабинета">
                {WORKSPACE_TABS.map(tab => (
                    <button
                        key={tab}
                        className={`workspace-tab${activeTab === tab ? ' active' : ''}`}
                        type="button"
                        onClick={() => switchTab(tab)}
                    >
                        {TAB_TITLES[tab]}
                        {tab === 'requests' && (
                            <span>{pendingCount(requestsState.items)}</span>
                        )}
                    </button>
                ))}
            </nav>

            <section className={`workspace-view${activeTab === 'schedule' ? ' active' : ''}`} hidden={activeTab !== 'schedule'}>
                <section className="toolbar">
                    <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="teacher"
                    />
                ) : (
                    <section className="schedule-overview" aria-live="polite">
                        {overviewState.kind === 'error' ? (
                            <AsyncState
                                kind="error"
                                title="Быстрый обзор"
                                message={overviewState.message || 'Не удалось загрузить ближайшие занятия'}
                            />
                        ) : (
                            <AsyncState kind="loading" title="Быстрый обзор" message="Загружаем ближайшие занятия…" />
                        )}
                    </section>
                )}

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

                <AbsencePanel />

                {scheduleState.kind === 'ready' ? (
                    <TeacherWeekGrid
                        lessons={scheduleState.lessons}
                        onRequestLesson={setDialogLesson}
                        weekStart={weekStart}
                    />
                ) : (
                    <TeacherWeekGrid
                        emptyMessage={scheduleState.kind === 'error' ? 'Ошибка загрузки' : 'Загрузка...'}
                        lessons={[]}
                        onRequestLesson={setDialogLesson}
                        weekStart={weekStart}
                    />
                )}
            </section>

            <section className={`workspace-view${activeTab === 'preferences' ? ' active' : ''}`} hidden={activeTab !== 'preferences'}>
                <PreferencesTab />
            </section>

            <section className={`workspace-view${activeTab === 'requests' ? ' active' : ''}`} hidden={activeTab !== 'requests'}>
                <RequestsTab
                    items={requestsState.items}
                    onCancel={handleCancelRequest}
                    onRefresh={() => void refreshRequests()}
                    stateKind={requestsState.kind}
                />
            </section>

            {dialogLesson && (
                <RequestDialog
                    lesson={dialogLesson}
                    onClose={() => setDialogLesson(null)}
                    onSubmitted={handleSubmitRequest}
                />
            )}
        </main>
    );
}

function scheduleStatus(scheduleState) {
    if (scheduleState.kind === 'error') {
        return scheduleState.message || 'Не удалось загрузить расписание';
    }
    if (scheduleState.kind === 'ready') {
        const count = scheduleState.lessons.length;
        return count > 0 ? `Найдено занятий: ${count}` : 'На этой неделе занятий нет';
    }
    return 'Загрузка расписания...';
}