'use strict';

const form = document.getElementById('chat-form');
const message = document.getElementById('chat-message');
const submit = document.getElementById('chat-submit');
const feedback = document.getElementById('chat-feedback');
const messages = document.getElementById('chat-log');
const chatWindow = document.getElementById('chat-window');
const chatEmpty = document.getElementById('chat-empty');
const ticketLabel = document.getElementById('chat-ticket');
const newConversation = document.getElementById('chat-new');
const chatView = document.getElementById('chat-view');
const exitView = document.getElementById('chat-exit-view');
const exitButton = document.getElementById('chat-exit');
const returnButton = document.getElementById('chat-return');
const staff = location.pathname === '/staff-chat';
const channel = staff ? 'staff' : 'users';
const sessionsUrl = `/api/chat/${channel}/sessions`;
const storageKey = `ege-support.chat.${channel}`;
const sessionIdPattern = /^[0-9a-f]{8}(?:-[0-9a-f]{4}){3}-[0-9a-f]{12}$/iu;
const roleLabels = { customer: 'Вы', staff: 'Вы', moderator: 'Модерация', operator: 'Поддержка' };
const timeFormat = new Intl.DateTimeFormat('ru-RU', { dateStyle: 'short', timeStyle: 'short' });

let conversation = loadConversation();
let attempt;
let sending = false;
let renderedCount = 0;
let exited = false;
let generation = 0;
let pollTimer;

function isCurrent(expected) {
  return !exited && generation === expected;
}

const title = staff ? 'Чат сотрудников' : 'Чат пользователей';
document.getElementById('chat-title').textContent = title;
document.title = `${title} · Онлайн-школа ЕГЭ`;

function loadConversation() {
  if (staff) {
    const params = new URLSearchParams(location.hash.slice(1));
    if (params.has('session')) {
      const id = params.get('session');
      history.replaceState(null, '', location.pathname + location.search);
      if (sessionIdPattern.test(id)) {
        const issued = { id, fromStaffSite: true };
        storeConversation(issued);
        return issued;
      }
    }
  }
  try {
    const saved = JSON.parse(localStorage.getItem(storageKey));
    if (typeof saved?.id === 'string' && sessionIdPattern.test(saved.id)) return saved;
  } catch {
    // The chat can still be used for the current tab when storage is unavailable.
  }
  return null;
}

function storeConversation(value) {
  try {
    if (value) localStorage.setItem(storageKey, JSON.stringify(value));
    else localStorage.removeItem(storageKey);
  } catch {
    // Keep the active conversation in memory when storage is unavailable.
  }
}

function setFeedback(text = '', error = false) {
  feedback.textContent = text;
  feedback.dataset.error = error;
}

async function request(url, body) {
  const options = body === undefined ? {} : {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(body),
  };
  let response;
  try {
    response = await fetch(url, options);
  } catch {
    throw new Error('Не удалось связаться с сервером. Повторите попытку.');
  }
  const data = await response.json().catch(() => null);
  if (!response.ok || !data) {
    const error = new Error(data?.error || 'Не удалось выполнить действие. Повторите попытку.');
    error.status = response.status;
    throw error;
  }
  return data;
}

function renderConversation(data, follow = false) {
  if (data.id !== conversation?.id || data.messages.length < renderedCount) return;
  const wasAtBottom = chatWindow.scrollHeight - chatWindow.scrollTop - chatWindow.clientHeight < 40;
  const fragment = document.createDocumentFragment();
  for (const item of data.messages.slice(renderedCount)) {
    const bubble = document.createElement('li');
    bubble.dataset.role = item.role;
    const meta = document.createElement('div');
    meta.className = 'chat-meta';
    const author = document.createElement('strong');
    author.textContent = roleLabels[item.role] || 'Участник';
    const time = document.createElement('time');
    time.dateTime = item.createdAt;
    time.textContent = timeFormat.format(new Date(item.createdAt));
    const text = document.createElement('p');
    text.textContent = item.text;
    meta.append(author, time);
    bubble.append(meta, text);
    fragment.append(bubble);
  }
  messages.append(fragment);
  renderedCount = data.messages.length;
  messages.hidden = renderedCount === 0;
  chatEmpty.hidden = renderedCount > 0;
  ticketLabel.textContent = data.ticketId ? `Обращение №${data.ticketId}` : 'Новое обращение';
  newConversation.hidden = !data.ticketId || Boolean(conversation.fromStaffSite);
  if (follow || wasAtBottom) chatWindow.scrollTop = chatWindow.scrollHeight;
}

function resetConversation() {
  conversation = null;
  attempt = null;
  renderedCount = 0;
  storeConversation(null);
  messages.replaceChildren();
  messages.hidden = true;
  chatEmpty.hidden = false;
  newConversation.hidden = true;
  ticketLabel.textContent = 'Новое обращение';
}

async function refreshConversation() {
  if (exited || !conversation || sending) return;
  const current = conversation;
  try {
    const data = await request(`${sessionsUrl}/${current.id}`);
    if (conversation === current) renderConversation(data);
  } catch (error) {
    if (conversation !== current || sending) return;
    if (error.status === 404) {
      resetConversation();
      setFeedback(current.fromStaffSite
        ? 'Откройте новую ссылку на чат в разделе поддержки сотрудников.'
        : 'Предыдущая переписка недоступна. Можно начать новое обращение.', true);
    } else if (!renderedCount) {
      setFeedback(error.message, true);
    }
  }
}

async function pollConversation() {
  const expected = generation;
  await refreshConversation();
  if (isCurrent(expected)) pollTimer = window.setTimeout(pollConversation, 2000);
}

function setSending(value) {
  sending = value;
  submit.disabled = value;
  message.disabled = value;
  newConversation.disabled = value;
  form.setAttribute('aria-busy', String(value));
  submit.textContent = value ? 'Отправляем…' : 'Отправить';
}

newConversation.addEventListener('click', () => {
  resetConversation();
  message.value = '';
  setFeedback();
  message.focus();
});

exitButton.addEventListener('click', () => {
  exited = true;
  generation += 1;
  window.clearTimeout(pollTimer);
  resetConversation();
  message.value = '';
  setFeedback();
  setSending(false);
  chatView.hidden = true;
  exitView.hidden = false;
  exitButton.hidden = true;
  returnButton.focus();
});

returnButton.addEventListener('click', () => {
  if (!exited) return;
  exited = false;
  chatView.hidden = false;
  exitView.hidden = true;
  exitButton.hidden = false;
  message.focus();
  pollConversation();
});

form.addEventListener('submit', async (event) => {
  event.preventDefault();
  if (exited) return;
  const expected = generation;
  const text = message.value.trim();
  if (!text || sending) {
    if (!text) setFeedback('Введите сообщение.', true);
    return;
  }
  if (!attempt || attempt.text !== text) attempt = { requestId: crypto.randomUUID(), text };
  setSending(true);
  setFeedback();
  try {
    if (!conversation) {
      const created = await request(sessionsUrl, {});
      if (!isCurrent(expected)) return;
      conversation = { id: created.id };
      storeConversation(conversation);
    }
    const updated = await request(`${sessionsUrl}/${conversation.id}/messages`, attempt);
    if (!isCurrent(expected)) return;
    renderConversation(updated, true);
    message.value = '';
    attempt = null;
    setFeedback('Сообщение отправлено.');
  } catch (error) {
    if (!isCurrent(expected)) return;
    if (error.status === 404 && conversation) {
      const needsLink = conversation.fromStaffSite;
      resetConversation();
      setFeedback(needsLink
        ? 'Откройте новую ссылку на чат в разделе поддержки сотрудников.'
        : 'Предыдущая переписка недоступна. Повторите отправку, чтобы начать новую.', true);
    } else if (staff && (error.status === 401 || error.status === 403)) {
      setFeedback('Откройте чат через раздел поддержки сотрудников на сайте.', true);
    } else {
      setFeedback(error.message, true);
    }
  } finally {
    if (isCurrent(expected)) {
      setSending(false);
      message.focus();
    }
  }
});

pollConversation();