export function renderScheduleOverviewState(container, { kind = 'loading', message = '', onRetry = null } = {}) {
    if (!container) return;
    const labels = {
        loading: message || 'Загружаем ближайшие занятия…',
        empty: message || 'В ближайшие дни занятий нет',
        error: message || 'Не удалось загрузить ближайшие занятия'
    };
    container.innerHTML = `
        <div class="schedule-overview-state is-${escapeHtml(kind)}" role="${kind === 'error' ? 'alert' : 'status'}">
            ${kind === 'loading' ? '<span class="schedule-overview-spinner" aria-hidden="true"></span>' : ''}
            <span>${escapeHtml(labels[kind] || message)}</span>
            ${kind === 'error' && onRetry ? '<button class="btn btn-md btn-secondary" type="button" data-overview-retry>Повторить</button>' : ''}
        </div>
    `;
    container.querySelector('[data-overview-retry]')?.addEventListener('click', onRetry);
}

export function renderScheduleOverview(container, lessons, { role = 'student', now = new Date(), onGoToday = null } = {}) {
    if (!container) return { todayCount: 0, hasNext: false };
    const { todayIso, todayLessons, nextLesson } = buildScheduleOverviewModel(lessons, now);

    container.innerHTML = `
        <header class="schedule-overview-head">
            <div>
                <span class="schedule-overview-kicker">Быстрый обзор</span>
                <h2>${escapeHtml(formatLongDate(now))}</h2>
            </div>
            <button class="btn btn-md btn-secondary" type="button" data-overview-today>Открыть текущую неделю</button>
        </header>
        <div class="schedule-overview-grid">
            <article class="schedule-overview-card is-today">
                <div class="schedule-overview-card-head">
                    <div>
                        <span>Сегодня</span>
                        <h3>${todayLessons.length ? pluralLessons(todayLessons.length) : 'Свободный день'}</h3>
                    </div>
                    <span class="schedule-overview-count">${todayLessons.length}</span>
                </div>
                <div class="schedule-overview-list">
                    ${todayLessons.length
                        ? todayLessons.map(lesson => renderCompactLesson(lesson, role)).join('')
                        : '<p class="schedule-overview-empty">На сегодня занятий нет.</p>'}
                </div>
            </article>
            <article class="schedule-overview-card is-next">
                <div class="schedule-overview-card-head">
                    <div>
                        <span>Следующая пара</span>
                        <h3>${nextLesson ? escapeHtml(relativeDate(nextLesson.date, todayIso)) : 'Пока ничего не запланировано'}</h3>
                    </div>
                    ${nextLesson ? `<span class="schedule-overview-badge">${lessonStart(nextLesson) <= now ? 'Идёт сейчас' : escapeHtml(trimTime(nextLesson.startTime))}</span>` : ''}
                </div>
                ${nextLesson ? renderNextLesson(nextLesson, role) : '<p class="schedule-overview-empty">В ближайшие 14 дней занятий нет.</p>'}
            </article>
        </div>
    `;
    container.querySelector('[data-overview-today]')?.addEventListener('click', onGoToday || (() => {}));
    return { todayCount: todayLessons.length, hasNext: Boolean(nextLesson) };
}

export function buildScheduleOverviewModel(lessons, now = new Date()) {
    const ordered = [...(lessons || [])].sort((left, right) => lessonStart(left) - lessonStart(right));
    const todayIso = toIsoDate(now);
    return {
        todayIso,
        todayLessons: ordered.filter(lesson => lesson.date === todayIso),
        nextLesson: ordered.find(lesson => lessonEnd(lesson) >= now) || null
    };
}

function renderCompactLesson(lesson, role) {
    return `
        <div class="schedule-overview-lesson">
            <time>${escapeHtml(trimTime(lesson.startTime))}</time>
            <div>
                <strong>${escapeHtml(lesson.subjectName || 'Занятие')}</strong>
                <small>${escapeHtml(lessonMeta(lesson, role).join(' · ') || 'Подробности уточняются')}</small>
            </div>
        </div>
    `;
}

function renderNextLesson(lesson, role) {
    return `
        <div class="schedule-overview-next">
            <div class="schedule-overview-next-time">
                <strong>${escapeHtml(trimTime(lesson.startTime))}</strong>
                <span>до ${escapeHtml(trimTime(lesson.endTime))}</span>
            </div>
            <div>
                <h4>${escapeHtml(lesson.subjectName || 'Занятие')}</h4>
                <p>${escapeHtml(lessonMeta(lesson, role).join(' · ') || 'Подробности уточняются')}</p>
                ${lesson.lessonTypeName ? `<span class="schedule-overview-type">${escapeHtml(lesson.lessonTypeName)}</span>` : ''}
            </div>
        </div>
    `;
}

function lessonMeta(lesson, role) {
    const groups = Array.isArray(lesson.groupNames) ? lesson.groupNames.join(', ') : '';
    const subgroup = Array.isArray(lesson.subgroupNames) ? lesson.subgroupNames.join(', ') : lesson.subgroupName;
    return role === 'teacher'
        ? [groups || subgroup, lesson.classroomName].filter(Boolean)
        : [lesson.teacherName, lesson.classroomName, subgroup].filter(Boolean);
}

function lessonStart(lesson) {
    return new Date(`${lesson.date}T${normalizeTime(lesson.startTime)}`);
}

function lessonEnd(lesson) {
    return new Date(`${lesson.date}T${normalizeTime(lesson.endTime || lesson.startTime)}`);
}

function normalizeTime(value) {
    const text = String(value || '00:00:00');
    return text.length === 5 ? `${text}:00` : text;
}

function relativeDate(value, todayIso) {
    if (value === todayIso) return 'Сегодня';
    const today = parseIsoDate(todayIso);
    const target = parseIsoDate(value);
    const dayDifference = Math.round((target - today) / 86400000);
    if (dayDifference === 1) return 'Завтра';
    return target.toLocaleDateString('ru-RU', { weekday: 'long', day: 'numeric', month: 'long' });
}

function parseIsoDate(value) {
    const [year, month, day] = String(value).split('-').map(Number);
    return new Date(year, month - 1, day);
}

function toIsoDate(date) {
    return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, '0')}-${String(date.getDate()).padStart(2, '0')}`;
}

function formatLongDate(date) {
    const value = date.toLocaleDateString('ru-RU', { weekday: 'long', day: 'numeric', month: 'long' });
    return value.charAt(0).toUpperCase() + value.slice(1);
}

function pluralLessons(count) {
    const mod10 = count % 10;
    const mod100 = count % 100;
    const noun = mod10 === 1 && mod100 !== 11 ? 'занятие' : mod10 >= 2 && mod10 <= 4 && (mod100 < 12 || mod100 > 14) ? 'занятия' : 'занятий';
    return `${count} ${noun}`;
}

function trimTime(value) {
    return String(value || '').slice(0, 5);
}

function escapeHtml(value) {
    return String(value ?? '')
        .replaceAll('&', '&amp;')
        .replaceAll('<', '&lt;')
        .replaceAll('>', '&gt;')
        .replaceAll('"', '&quot;')
        .replaceAll("'", '&#039;');
}