import { api } from '../api.js';
import { escapeHtml, showAlert, hideAlert } from '../utils.js';

const ROLE_DEPARTMENT = 'DEPARTMENT';
const PARITY_LABELS = {
    BOTH: 'каждая',
    ODD: 'нечётная',
    EVEN: 'чётная'
};
const DAY_SHORT_LABELS = {
    1: 'Пн',
    2: 'Вт',
    3: 'Ср',
    4: 'Чт',
    5: 'Пт',
    6: 'Сб',
    7: 'Вс'
};
const DAY_FULL_LABELS = {
    1: 'Понедельник',
    2: 'Вторник',
    3: 'Среда',
    4: 'Четверг',
    5: 'Пятница',
    6: 'Суббота',
    7: 'Воскресенье'
};
const DAY_ORDER = [1, 2, 3, 4, 5, 6, 7];
const CELL_PARITY_LAYOUT = [
    { parity: 'ODD', label: 'Нечётная' },
    { parity: 'EVEN', label: 'Чётная' }
];
const SPLIT_AUTO = 'auto';
const SPLIT_GROUPS = 'groups';
const SPLIT_TEACHERS = 'teachers';
const SPLIT_CLASSROOMS = 'classrooms';

export async function initScheduleView() {
    const role = localStorage.getItem('role');
    const userDepartmentId = localStorage.getItem('departmentId');
    const dateInput = document.getElementById('schedule-view-date');
    const loadButton = document.getElementById('schedule-view-load');
    const departmentField = document.getElementById('schedule-view-department-field');
    const departmentSelect = document.getElementById('schedule-view-department');
    const tables = document.getElementById('schedule-view-tables');
    const countLabel = document.getElementById('schedule-view-count');

    setDefaultDate(dateInput);
    loadButton?.addEventListener('click', loadData);

    try {
        await loadDictionaries(role, userDepartmentId);
        if (role === ROLE_DEPARTMENT) {
            departmentField.hidden = true;
            departmentSelect.value = userDepartmentId || '';
        }
        await loadData();
    } catch (error) {
        setTableState(error.message || 'Ошибка загрузки справочников');
    }

    async function loadData() {
        hideAlert('schedule-view-alert');
        setTableState('Загрузка...');
        countLabel.textContent = 'Загрузка...';

        if (!dateInput.value) {
            const message = 'Выберите дату в периоде';
            showAlert('schedule-view-alert', message, 'error');
            setTableState(message);
            countLabel.textContent = '0 занятий';
            return;
        }
        const range = twoWeekRange(dateInput.value);
        const params = new URLSearchParams({
            startDate: range.startDate,
            endDate: range.endDate
        });
        addOptional(params, 'groupId', valueOf('schedule-view-group'));
        addOptional(params, 'teacherId', valueOf('schedule-view-teacher'));
        addOptional(params, 'classroomId', valueOf('schedule-view-classroom'));
        addOptional(params, 'departmentId', role === ROLE_DEPARTMENT ? userDepartmentId : departmentSelect.value);
        addOptional(params, 'subjectId', valueOf('schedule-view-subject'));
        addOptional(params, 'lessonTypeId', valueOf('schedule-view-lesson-type'));
        addOptional(params, 'parity', valueOf('schedule-view-parity'));

        try {
            const lessons = await api.get(`/api/schedule/search?${params}`);
            renderLessons(lessons, range);
        } catch (error) {
            const message = error.message || 'Ошибка загрузки расписания';
            showAlert('schedule-view-alert', message, 'error');
            setTableState(message);
            countLabel.textContent = '0 занятий';
        }
    }

    function renderLessons(lessons, range) {
        countLabel.textContent = lessonCountLabel(lessons.length);
        if (!lessons.length) {
            setTableState('Занятия не найдены');
            return;
        }
        const sections = buildScheduleSections(lessons);
        if (!sections.length) {
            setTableState('Нет данных для выбранного разреза таблиц');
            return;
        }
        const tableCount = sections.reduce((count, section) =>
            count + buildCombinedWeekBlocks(range.startDate, range.endDate, section.lessons).length, 0
        );
        if (!tableCount) {
            setTableState('Выберите корректный период');
            return;
        }
        countLabel.textContent = `${lessonCountLabel(lessons.length)}, ${tableCountLabel(tableCount)}`;
        tables.innerHTML = sections
            .map(section => renderScheduleSection(section, range))
            .join('');
    }

    function renderScheduleSection(section, range) {
        const slots = collectSlots(section.lessons);
        const lessonsByDateSlot = groupLessonsByDateSlot(section.lessons);
        const blocks = buildCombinedWeekBlocks(range.startDate, range.endDate, section.lessons);
        return blocks
            .map(block => renderCombinedWeekTable(block, slots, lessonsByDateSlot, section))
            .join('');
    }

    function renderCombinedWeekTable(block, slots, lessonsByDateSlot, section) {
        const dayHeaders = DAY_ORDER.map(day => `
            <th class="room-day-cell">
                <strong>${escapeHtml(dayShort(day))}</strong>
                <span>${escapeHtml(DAY_FULL_LABELS[day] || '')}</span>
                <div class="room-day-parity-dates">
                    ${CELL_PARITY_LAYOUT.map(({ parity, label }) => renderDayParityDate(block.datesByDay[day]?.[parity], label)).join('')}
                </div>
            </th>
        `).join('');
        const rows = slots.map(slot => `
            <tr>
                <td class="room-time-cell">
                    <strong>${escapeHtml(slot.orderLabel)}</strong>
                    <span>${escapeHtml(slot.timeLabel)}</span>
                    ${slot.id ? `<small>ID ${escapeHtml(slot.id)}</small>` : ''}
                </td>
                ${DAY_ORDER.map(day => renderCombinedSlotCell(block.datesByDay[day] || {}, slot, lessonsByDateSlot)).join('')}
            </tr>
        `).join('');

        return `
            <section class="schedule-view-week-panel">
                <div class="room-week-heading">
                    <h3>${escapeHtml(section.title)} · ${escapeHtml(block.label)}</h3>
                    <span>${escapeHtml(`${lessonCountLabel(section.lessons.length)}; ${combinedWeekCaption(block)}`)}</span>
                </div>
                <div class="workload-grid-container schedule-view-grid-container">
                    <table class="workload-table room-week-table schedule-view-matrix-table">
                        <thead>
                            <tr>
                                <th class="room-time-heading">Время</th>
                                ${dayHeaders}
                            </tr>
                        </thead>
                        <tbody>${rows}</tbody>
                    </table>
                </div>
            </section>
        `;
    }

    function renderDayParityDate(date, label) {
        return `<span>${escapeHtml(label)}: ${date ? escapeHtml(formatDateShort(date)) : '-'}</span>`;
    }

    function renderCombinedSlotCell(datesByParity, slot, lessonsByDateSlot) {
        const states = CELL_PARITY_LAYOUT.map(({ parity, label }) => ({
            parity,
            label,
            state: scheduleSlotState(datesByParity[parity], slot, lessonsByDateSlot)
        }));

        if (slotStatesEqual(states[0].state, states[1].state)) {
            return `<td class="room-combined-cell room-single-cell">${renderUnifiedSlot(states[0].state)}</td>`;
        }

        const halves = states.map(({ parity, label, state }) =>
            renderSlotHalf(state, parity, label)
        ).join('');
        return `<td class="room-combined-cell">${halves}</td>`;
    }

    function scheduleSlotState(date, slot, lessonsByDateSlot) {
        if (!date) {
            return { kind: 'empty', lessons: [] };
        }
        const lessons = lessonsByDateSlot.get(dateSlotKey(date, slot.key)) || [];
        if (lessons.length) {
            return { kind: 'busy', lessons };
        }
        return { kind: 'free', lessons: [] };
    }

    function renderUnifiedSlot(state) {
        if (state.kind === 'busy') {
            return `<div class="room-week-unified room-week-unified-busy">${state.lessons.map(renderLessonCard).join('')}</div>`;
        }
        if (state.kind === 'empty') {
            return '<div class="room-week-unified room-week-unified-empty"><span class="slot-unavailable">Нет даты</span></div>';
        }
        return '<div class="room-week-unified room-week-unified-free"><span class="free-slot">Нет занятий</span></div>';
    }

    function renderSlotHalf(state, parity, label) {
        if (state.kind === 'busy') {
            return `
                <div class="room-week-half room-week-half-${parity.toLowerCase()} room-week-half-busy">
                    <span class="room-half-marker">${escapeHtml(label)}</span>
                    ${state.lessons.map(renderLessonCard).join('')}
                </div>
            `;
        }
        if (state.kind === 'empty') {
            return `
                <div class="room-week-half room-week-half-${parity.toLowerCase()} room-week-half-empty">
                    <span class="room-half-marker">${escapeHtml(label)}</span>
                    <span class="slot-unavailable">Нет даты</span>
                </div>
            `;
        }
        return `
            <div class="room-week-half room-week-half-${parity.toLowerCase()} room-week-half-free">
                <span class="room-half-marker">${escapeHtml(label)}</span>
                <span class="free-slot">Нет занятий</span>
            </div>
        `;
    }

    function slotStatesEqual(first, second) {
        if (first.kind !== second.kind) return false;
        if (first.kind !== 'busy') return true;
        return lessonSetSignature(first.lessons) === lessonSetSignature(second.lessons);
    }

    function lessonSetSignature(lessons) {
        return lessons
            .map(lessonContentSignature)
            .sort((a, b) => naturalCompare(a, b))
            .join('|');
    }

    function lessonContentSignature(lesson) {
        return [
            lesson.scheduleRuleSlotId || lesson.scheduleRuleId || '',
            lesson.subjectId || lesson.subjectName || '',
            lesson.teacherId || lesson.teacherName || '',
            lesson.classroomId || lesson.classroomName || '',
            lesson.lessonTypeId || lesson.lessonTypeName || '',
            lesson.lessonFormat || '',
            valueListSignature(lesson.groupIds, lesson.groupNames),
            valueListSignature(lesson.subgroupIds, lesson.subgroupNames)
        ].join(':');
    }

    function valueListSignature(primary = [], fallback = []) {
        const primaryList = Array.isArray(primary) ? primary : [];
        const fallbackList = Array.isArray(fallback) ? fallback : [];
        const source = primaryList.length ? primaryList : fallbackList;
        return [...source]
            .map(value => String(value))
            .sort((a, b) => naturalCompare(a, b))
            .join(',');
    }

    function renderLessonCard(lesson) {
        const subgroupText = (lesson.subgroupNames || []).join(', ');
        const meta = [
            lesson.lessonTypeName,
            lesson.lessonFormat,
            PARITY_LABELS[lesson.parity] || lesson.parity
        ].filter(Boolean).join(' · ');

        return `
            <div class="lesson-card schedule-view-lesson-card">
                <div class="lesson-subject">${escapeHtml(lesson.subjectName || 'Без дисциплины')}</div>
                <div class="lesson-group">${escapeHtml((lesson.groupNames || []).join(', ') || 'Группа не указана')}</div>
                ${subgroupText ? `<div class="lesson-subgroup">${escapeHtml(subgroupText)}</div>` : ''}
                <div class="lesson-teacher">${escapeHtml(lesson.teacherName || 'Преподаватель не указан')}</div>
                <div class="lesson-meta">${escapeHtml(lesson.classroomName || 'Аудитория не указана')}</div>
                ${meta ? `<div class="lesson-meta">${escapeHtml(meta)}</div>` : ''}
                ${lesson.scheduleRuleSlotId ? `<div class="lesson-meta">ID слота: ${escapeHtml(lesson.scheduleRuleSlotId)}</div>` : ''}
            </div>
        `;
    }

    function setTableState(message) {
        if (!tables) return;
        tables.innerHTML = `<div class="loading-row schedule-view-state">${escapeHtml(message)}</div>`;
    }
}

async function loadDictionaries(role, userDepartmentId) {
    const [groups, teachers, classrooms, departments, subjects, lessonTypes] = await Promise.all([
        api.get('/api/groups'),
        api.get('/api/users/teachers'),
        api.get('/api/classrooms'),
        api.get('/api/departments'),
        api.get('/api/subjects'),
        api.get('/api/lesson-types')
    ]);

    fillSelect('schedule-view-group', groups, item => item.id, item => item.name, 'Все группы');
    fillSelect('schedule-view-teacher', teachers, item => item.id, item => item.fullName || item.username, 'Все преподаватели');
    fillSelect('schedule-view-classroom', classrooms, item => item.id, item => roomLabel(item), 'Все аудитории');
    fillSelect('schedule-view-department', departments, item => item.id, item => item.departmentName, 'Все кафедры');
    fillSelect('schedule-view-subject', subjects, item => item.id, item => item.name, 'Все дисциплины');
    fillSelect('schedule-view-lesson-type', lessonTypes, item => item.id, item => item.name, 'Все типы');

    if (role === ROLE_DEPARTMENT && userDepartmentId) {
        document.getElementById('schedule-view-department').value = userDepartmentId;
    }
}

function setDefaultDate(dateInput) {
    const today = new Date();
    dateInput.value = toIsoDate(today);
}

function fillSelect(id, items, valueFn, labelFn, emptyLabel) {
    const select = document.getElementById(id);
    if (!select) return;
    select.innerHTML = `<option value="">${escapeHtml(emptyLabel)}</option>` +
        (items || []).map(item => `<option value="${escapeHtml(valueFn(item))}">${escapeHtml(labelFn(item))}</option>`).join('');
}

function addOptional(params, key, value) {
    if (value) params.set(key, value);
}

function valueOf(id) {
    return document.getElementById(id)?.value || '';
}

function roomLabel(room) {
    return [room.name, room.building, room.floor ? `${room.floor} этаж` : null].filter(Boolean).join(' · ');
}

function collectSlots(lessons) {
    const slots = new Map();
    lessons.forEach(lesson => {
        const key = lessonSlotKey(lesson);
        const existing = slots.get(key);
        const next = {
            key,
            id: lesson.timeSlotId,
            orderNumber: lesson.timeSlotOrder,
            startTime: lesson.startTime,
            endTime: lesson.endTime,
            orderLabel: lesson.timeSlotOrder ? `${lesson.timeSlotOrder} пара` : 'Пара',
            timeLabel: lesson.startTime || lesson.endTime
                ? `${trimTime(lesson.startTime)}-${trimTime(lesson.endTime)}`
                : 'Время не указано'
        };
        if (!existing || existing.timeLabel === 'Время не указано') {
            slots.set(key, next);
        }
    });
    return Array.from(slots.values()).sort(compareSlots);
}

function groupLessonsByDateSlot(lessons) {
    const grouped = new Map();
    lessons.forEach(lesson => {
        if (!lesson.date) return;
        const key = dateSlotKey(lesson.date, lessonSlotKey(lesson));
        if (!grouped.has(key)) grouped.set(key, []);
        grouped.get(key).push(lesson);
    });
    grouped.forEach(items => {
        items.sort((a, b) => naturalCompare(a.subjectName, b.subjectName)
            || naturalCompare(a.teacherName, b.teacherName)
            || naturalCompare((a.groupNames || []).join(','), (b.groupNames || []).join(',')));
    });
    return grouped;
}

function buildScheduleSections(lessons) {
    const splitType = resolveSplitType();
    const sections = new Map();

    lessons.forEach(lesson => {
        splitEntitiesForLesson(lesson, splitType).forEach(entity => {
            if (!sections.has(entity.key)) {
                sections.set(entity.key, {
                    key: entity.key,
                    title: entity.title,
                    lessons: []
                });
            }
            sections.get(entity.key).lessons.push(lesson);
        });
    });

    return Array.from(sections.values())
        .map(section => ({
            ...section,
            lessons: sortLessons(section.lessons)
        }))
        .sort((a, b) => naturalCompare(a.title, b.title));
}

function resolveSplitType() {
    const requested = valueOf('schedule-view-split');
    if ([SPLIT_GROUPS, SPLIT_TEACHERS, SPLIT_CLASSROOMS].includes(requested)) {
        return requested;
    }
    if (valueOf('schedule-view-teacher')) return SPLIT_TEACHERS;
    if (valueOf('schedule-view-classroom')) return SPLIT_CLASSROOMS;
    return SPLIT_GROUPS;
}

function splitEntitiesForLesson(lesson, splitType) {
    if (splitType === SPLIT_TEACHERS) {
        return [singleEntity('teacher', lesson.teacherId, lesson.teacherName, 'Преподаватель не указан')];
    }
    if (splitType === SPLIT_CLASSROOMS) {
        return [singleEntity('classroom', lesson.classroomId, lesson.classroomName, 'Аудитория не указана')];
    }
    return listEntities('group', lesson.groupIds, lesson.groupNames, 'Группа не указана');
}

function singleEntity(prefix, id, name, fallback) {
    const title = name || fallback;
    return {
        key: `${prefix}:${id ?? title}`,
        title
    };
}

function listEntities(prefix, ids = [], names = [], fallback) {
    const safeIds = Array.isArray(ids) ? ids : [];
    const safeNames = Array.isArray(names) ? names : [];
    if (!safeIds.length && !safeNames.length) {
        return [singleEntity(prefix, null, fallback, fallback)];
    }
    const maxLength = Math.max(safeIds.length, safeNames.length);
    const entities = [];
    for (let index = 0; index < maxLength; index += 1) {
        const id = safeIds[index] ?? null;
        const name = safeNames[index] || (id == null ? fallback : `Группа ${id}`);
        entities.push(singleEntity(prefix, id, name, fallback));
    }
    return entities;
}

function sortLessons(lessons) {
    return [...lessons].sort((a, b) =>
        naturalCompare(a.date, b.date)
        || compareSlots(lessonSlotDescriptor(a), lessonSlotDescriptor(b))
        || naturalCompare(a.subjectName, b.subjectName)
        || naturalCompare(a.teacherName, b.teacherName)
        || naturalCompare(a.classroomName, b.classroomName)
    );
}

function lessonSlotDescriptor(lesson) {
    return {
        key: lessonSlotKey(lesson),
        orderNumber: lesson.timeSlotOrder,
        startTime: lesson.startTime
    };
}

function buildCombinedWeekBlocks(startDate, endDate, lessons) {
    const dates = datesBetween(startDate, endDate);
    const weekGroups = new Map();
    dates.forEach(date => {
        const key = weekStart(date);
        if (!weekGroups.has(key)) weekGroups.set(key, []);
        weekGroups.get(key).push(date);
    });

    const weekStarts = Array.from(weekGroups.keys()).sort((a, b) => naturalCompare(a, b));
    const blocks = [];
    for (let index = 0; index < weekStarts.length; index += 2) {
        const firstWeek = weekGroups.get(weekStarts[index]) || [];
        const secondWeek = weekGroups.get(weekStarts[index + 1]) || [];
        const blockDates = [...firstWeek, ...secondWeek];
        const firstParity = weekParity(firstWeek, lessons) || 'ODD';
        const secondParity = weekParity(secondWeek, lessons) || (firstParity === 'ODD' ? 'EVEN' : 'ODD');
        const datesWithFallback = [
            ...firstWeek.map(date => ({ date, fallbackParity: firstParity })),
            ...secondWeek.map(date => ({ date, fallbackParity: secondParity }))
        ];
        blocks.push({
            startDate: blockDates[0],
            endDate: blockDates[blockDates.length - 1],
            datesByDay: buildDatesByDay(datesWithFallback, lessons),
            label: `Период ${formatDate(blockDates[0])} - ${formatDate(blockDates[blockDates.length - 1])}`
        });
    }
    return blocks;
}

function weekParity(dates, lessons) {
    for (const date of dates) {
        const parity = parityForDate(date, lessons);
        if (parity) return parity;
    }
    return null;
}

function buildDatesByDay(datesWithFallback, lessons) {
    const datesByDay = {};
    datesWithFallback.forEach(({ date, fallbackParity }) => {
        const day = isoDay(date);
        const parity = parityForDate(date, lessons) || fallbackParity;
        if (!datesByDay[day]) datesByDay[day] = {};
        datesByDay[day][parity] = date;
    });
    return datesByDay;
}

function parityForDate(date, lessons) {
    const lesson = lessons.find(item => item.date === date && ['ODD', 'EVEN'].includes(item.parity));
    if (lesson?.parity) return lesson.parity;
    const withWeek = lessons.find(item => item.date === date && item.weekNumber != null);
    if (withWeek?.weekNumber != null) return Number(withWeek.weekNumber) % 2 === 0 ? 'EVEN' : 'ODD';
    return null;
}

function combinedWeekCaption(block) {
    return CELL_PARITY_LAYOUT
        .map(({ parity, label }) => {
            const dates = DAY_ORDER.map(day => block.datesByDay[day]?.[parity]).filter(Boolean);
            if (!dates.length) return `${label}: дат нет`;
            return `${label}: ${formatDate(dates[0])} - ${formatDate(dates[dates.length - 1])}`;
        })
        .join('; ');
}

function lessonSlotKey(lesson) {
    const value = lesson.timeSlotOrder ?? lesson.timeSlotId ?? `${lesson.startTime || ''}-${lesson.endTime || ''}`;
    return value ? String(value) : 'unknown';
}

function dateSlotKey(date, slotKey) {
    return `${date}:${slotKey}`;
}

function weekStart(value) {
    const date = parseIsoDate(value);
    const day = date.getDay() || 7;
    date.setDate(date.getDate() + 1 - day);
    return toIsoDate(date);
}

function twoWeekRange(value) {
    const selected = parseIsoDate(value);
    const start = addDays(selected, 1 - isoDay(value));
    const end = addDays(start, 13);
    return {
        startDate: toIsoDate(start),
        endDate: toIsoDate(end)
    };
}

function addDays(date, days) {
    const next = new Date(date);
    next.setDate(next.getDate() + days);
    return next;
}

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

function datesBetween(startDate, endDate) {
    const dates = [];
    for (let date = parseIsoDate(startDate); date <= parseIsoDate(endDate); date.setDate(date.getDate() + 1)) {
        dates.push(toIsoDate(date));
    }
    return dates;
}

function isoDay(value) {
    const day = parseIsoDate(value).getDay();
    return day === 0 ? 7 : day;
}

function dayShort(dayOfWeek) {
    return DAY_SHORT_LABELS[Number(dayOfWeek)] || '-';
}

function formatDate(value) {
    if (!value) return '-';
    const [year, month, day] = String(value).split('-');
    return `${day}.${month}.${year}`;
}

function formatDateShort(value) {
    const [, month, day] = String(value).split('-');
    return `${day}.${month}`;
}

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

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

function lessonCountLabel(count) {
    const tail = count % 100;
    if (tail >= 11 && tail <= 14) return `${count} занятий`;
    if (count % 10 === 1) return `${count} занятие`;
    if ([2, 3, 4].includes(count % 10)) return `${count} занятия`;
    return `${count} занятий`;
}

function tableCountLabel(count) {
    const tail = count % 100;
    if (tail >= 11 && tail <= 14) return `${count} таблиц`;
    if (count % 10 === 1) return `${count} таблица`;
    if ([2, 3, 4].includes(count % 10)) return `${count} таблицы`;
    return `${count} таблиц`;
}

function compareSlots(a, b) {
    const first = Number(a.orderNumber || a.key);
    const second = Number(b.orderNumber || b.key);
    if (!Number.isNaN(first) && !Number.isNaN(second) && first !== second) {
        return first - second;
    }
    return naturalCompare(a.startTime, b.startTime)
        || naturalCompare(a.key, b.key);
}

function naturalCompare(a, b) {
    return String(a || '').localeCompare(String(b || ''), 'ru', { numeric: true, sensitivity: 'base' });
}