/**
 * chat-drawer.ts — bottom sheet chat UI.
 *
 * Display:
 *  - We clone the existing chat scrollback (if found) and render into our
 *    own <ul>-style list. We update it every 1.5s by re-cloning the source.
 *  - We do NOT move the original node — we read-only display.
 *
 * Send (the clever bit):
 *  - Our composer dispatches a real InputEvent + KeyboardEvent(Enter) on
 *    the original site's chat textarea + a click on its submit button.
 *  - That keeps every server-side guard (rate limit, mute, profanity)
 *    intact — the React reducer thinks the user typed in their UI.
 *  - If the React flow is broken (e.g. their chat was redesigned), the WS
 *    proxy can fall back to a direct socket send.
 */

import { SITE, pick } from './util/selectors';
import { ensureHost } from './layout';

type State = 'closed' | 'peek' | 'open';

interface DrawerContext {
  root: HTMLElement;
  fab: HTMLButtonElement;
  sheet: HTMLDivElement;
  backdrop: HTMLDivElement;
  scroll: HTMLDivElement;
  composer: HTMLFormElement;
  textarea: HTMLTextAreaElement;
  sendBtn: HTMLButtonElement;
  closeBtn: HTMLButtonElement;
  preview: HTMLDivElement;
  state: State;
  pollTimer: number | null;
}

let ctx: DrawerContext | null = null;

function buildDrawer(): DrawerContext {
  const host = ensureHost();

  const fab = document.createElement('button');
  fab.className = 'bbp-fab';
  fab.setAttribute('aria-label', 'Open chat');
  fab.setAttribute('aria-expanded', 'false');
  fab.innerHTML = '💬<span class="bbp-fab__badge" hidden>0</span>';

  const backdrop = document.createElement('div');
  backdrop.className = 'bbp-backdrop';
  backdrop.setAttribute('data-open', 'false');

  const sheet = document.createElement('div');
  sheet.className = 'bbp-sheet';
  sheet.setAttribute('data-state', 'closed');
  sheet.setAttribute('role', 'dialog');
  sheet.setAttribute('aria-modal', 'false');
  sheet.setAttribute('aria-label', 'Chat');
  sheet.innerHTML = `
    <div class="bbp-sheet__handle" aria-hidden="true"></div>
    <div class="bbp-sheet__head">
      <div class="bbp-sheet__title">Chat</div>
      <button class="bbp-sheet__close" aria-label="Close chat">×</button>
    </div>
    <div class="bbp-sheet__peek-preview">Say something…</div>
    <div class="bbp-sheet__scroll" aria-live="polite"></div>
    <form class="bbp-composer">
      <textarea placeholder="Type a message…" rows="1" aria-label="Chat message"></textarea>
      <button type="submit" aria-label="Send">Send</button>
    </form>
  `;

  host.appendChild(backdrop);
  host.appendChild(sheet);
  host.appendChild(fab);

  const scroll = sheet.querySelector<HTMLDivElement>('.bbp-sheet__scroll')!;
  const composer = sheet.querySelector<HTMLFormElement>('.bbp-composer')!;
  const textarea = composer.querySelector<HTMLTextAreaElement>('textarea')!;
  const sendBtn = composer.querySelector<HTMLButtonElement>('button')!;
  const preview = sheet.querySelector<HTMLDivElement>('.bbp-sheet__peek-preview')!;
  const closeBtn = sheet.querySelector<HTMLButtonElement>('.bbp-sheet__close')!;

  const state: State = 'closed';
  return {
    root: host,
    fab,
    sheet,
    backdrop,
    scroll,
    composer,
    textarea,
    sendBtn,
    closeBtn,
    preview,
    state,
    pollTimer: null,
  };
}

function setState(c: DrawerContext, next: State): void {
  c.state = next;
  c.sheet.setAttribute('data-state', next);
  c.fab.setAttribute('aria-expanded', next === 'open' ? 'true' : 'false');
  c.backdrop.setAttribute('data-open', next === 'open' ? 'true' : 'false');
  c.backdrop.style.pointerEvents = next === 'open' ? 'auto' : 'none';
}

function findSiteChatNodes(): { scrollback: Element | null; input: HTMLTextAreaElement | null; sendBtn: HTMLButtonElement | null } {
  const scrollback =
    pick(SITE.chatScrollbackCandidates) ||
    // fallback: any element containing > 3 <p>/<span>/<div> children with chat-like text
    (() => {
      const cands = Array.from(document.querySelectorAll('ul, ol, [role="list"], [role="log"]'));
      return cands.find((c) => c.children.length > 2) ?? null;
    })();

  const input = pick<HTMLTextAreaElement>(SITE.chatInputCandidates);
  const sendBtn = pick<HTMLButtonElement>(SITE.sendButtonCandidates);
  return { scrollback, input, sendBtn };
}

function renderScrollback(c: DrawerContext, source: Element): void {
  // Clone source children, strip their CSS classes but keep their text.
  const frag = document.createDocumentFragment();
  const children = Array.from(source.children).slice(-50);
  for (const child of children) {
    const div = document.createElement('div');
    div.className = 'bbp-msg';
    // Keep inner structure; chat users want basic formatting.
    div.innerHTML = child.innerHTML;
    frag.appendChild(div);
  }
  // Avoid clobbering user's scroll position if they've scrolled up
  const atBottom =
    c.scroll.scrollHeight - c.scroll.scrollTop - c.scroll.clientHeight < 80;
  c.scroll.innerHTML = '';
  c.scroll.appendChild(frag);
  if (atBottom) c.scroll.scrollTop = c.scroll.scrollHeight;

  // Update peek preview with last message text
  const lastText = (children[children.length - 1]?.textContent ?? '').trim();
  c.preview.textContent = lastText.length > 0 ? lastText : 'Say something…';
}

function startPolling(c: DrawerContext): void {
  if (c.pollTimer) return;
  c.pollTimer = window.setInterval(() => {
    const { scrollback } = findSiteChatNodes();
    if (scrollback && scrollback.children.length > 0) {
      renderScrollback(c, scrollback);
    } else {
      c.scroll.innerHTML = '';
    }
  }, 1500);
}

function stopPolling(c: DrawerContext): void {
  if (c.pollTimer) {
    clearInterval(c.pollTimer);
    c.pollTimer = null;
  }
}

function sendViaSiteChat(_c: DrawerContext, text: string): boolean {
  const { input, sendBtn } = findSiteChatNodes();
  if (!input) return false;
  // Set value via the React-friendly path (avoids React's value-caching issue)
  const setter = Object.getOwnPropertyDescriptor(
    HTMLTextAreaElement.prototype,
    'value',
  )?.set;
  setter?.call(input, text);
  input.dispatchEvent(new Event('input', { bubbles: true }));

  // Prefer the site's own submit button. Fall back to Enter key.
  if (sendBtn) {
    sendBtn.click();
    return true;
  }
  input.dispatchEvent(
    new KeyboardEvent('keydown', { key: 'Enter', code: 'Enter', bubbles: true }),
  );
  return true;
}

function wireEvents(c: DrawerContext): void {
  c.fab.addEventListener('click', () => {
    setState(c, c.state === 'closed' ? 'open' : 'closed');
    if (c.state === 'open') {
      startPolling(c);
      c.textarea.focus();
    } else {
      stopPolling(c);
    }
  });

  c.closeBtn.addEventListener('click', () => setState(c, 'closed'));
  c.backdrop.addEventListener('click', () => setState(c, 'closed'));

  // Tap on the peek-strip opens the sheet
  c.preview.addEventListener('click', () => {
    if (c.state === 'peek') setState(c, 'open');
  });

  // Drag handle: simple toggle between peek/open. Real swipe gesture is out of V1.
  c.sheet.querySelector('.bbp-sheet__handle')!.addEventListener('click', () => {
    if (c.state === 'closed') setState(c, 'peek');
    else if (c.state === 'peek') setState(c, 'open');
    else setState(c, 'closed');
    if (c.state === 'open') startPolling(c);
    else if (c.state === 'closed') stopPolling(c);
  });

  c.composer.addEventListener('submit', (e) => {
    e.preventDefault();
    const text = c.textarea.value.trim();
    if (!text) return;
    c.sendBtn.disabled = true;
    const ok = sendViaSiteChat(c, text);
    // Optimistic UX: clear input whether or not it actually lands.
    c.textarea.value = '';
    if (!ok) {
      c.textarea.placeholder = 'Chat not available right now';
    }
    setTimeout(() => (c.sendBtn.disabled = false), 300);
  });

  // Auto-grow textarea on input
  c.textarea.addEventListener('input', () => {
    c.textarea.style.height = 'auto';
    c.textarea.style.height = Math.min(c.textarea.scrollHeight, 120) + 'px';
  });
}

export function mountDrawer(): void {
  if (ctx) return;
  ctx = buildDrawer();
  wireEvents(ctx);
  // Start in peek mode after a short delay so we don't flash during route load
  setTimeout(() => {
    if (ctx) setState(ctx, 'peek');
  }, 800);
}

export function unmountDrawer(): void {
  if (!ctx) return;
  stopPolling(ctx);
  ctx.fab.remove();
  ctx.sheet.remove();
  ctx.backdrop.remove();
  ctx = null;
}