import { useEffect, useRef } from 'react';
import { useSetAtom } from 'jotai';
import { Icons } from 'folds';
import { isTauri } from './useTauri';
import { ua } from '../utils/user-agent';
import { dismissToastAtom, toastQueueAtom } from '../state/toast';
import { installHintKind, shouldShowInstallHint } from '../utils/pwaInstall';

const VISITS_KEY = 'pwa-install-visits';
const DISMISSED_KEY = 'pwa-install-dismissed-at';
const SESSION_COUNTED_KEY = 'pwa-install-visit-counted';
const TOAST_ID = 'pwa-install-hint';
// Give the browser a moment to fire beforeinstallprompt (Chromium does so
// shortly after load once the manifest checks pass) before deciding which hint.
const DECIDE_DELAY_MS = 6000;

type BeforeInstallPromptEvent = Event & {
  prompt: () => Promise<void>;
  userChoice: Promise<{ outcome: 'accepted' | 'dismissed' }>;
};

const readNumber = (key: string): number | null => {
  try {
    const raw = localStorage.getItem(key);
    if (raw === null) return null;
    const n = Number(raw);
    return Number.isFinite(n) ? n : null;
  } catch {
    return null;
  }
};

const write = (key: string, value: string): void => {
  try {
    localStorage.setItem(key, value);
  } catch {
    /* blocked storage — the hint just won't be remembered */
  }
};

/** One visit per browser session (tab lifetime), not per React mount. */
const countVisit = (): number => {
  try {
    if (sessionStorage.getItem(SESSION_COUNTED_KEY)) return readNumber(VISITS_KEY) ?? 1;
    sessionStorage.setItem(SESSION_COUNTED_KEY, '1');
  } catch {
    return readNumber(VISITS_KEY) ?? 1;
  }
  const next = (readNumber(VISITS_KEY) ?? 0) + 1;
  write(VISITS_KEY, String(next));
  return next;
};

const isStandalone = (): boolean =>
  window.matchMedia?.('(display-mode: standalone)').matches === true ||
  (navigator as Navigator & { standalone?: boolean }).standalone === true;

const isIosSafari = (): boolean => {
  const { os, browser } = ua();
  return os.name === 'iOS' && (browser.name ?? '').includes('Safari');
};

/**
 * [Gitea #116] Offer to install the PWA: a real prompt on Chromium (deferred
 * `beforeinstallprompt`), Share-sheet instructions on iOS Safari, nothing
 * elsewhere. Shown as a sticky toast from the second visit, snoozed 30 days on
 * dismiss, never in Tauri or an installed PWA. Mount once for signed-in users.
 */
export function usePwaInstallPrompt(): void {
  const enqueueToast = useSetAtom(toastQueueAtom);
  const dismissToast = useSetAtom(dismissToastAtom);
  const deferredRef = useRef<BeforeInstallPromptEvent | null>(null);

  useEffect(() => {
    if (isTauri() || isStandalone()) return undefined;

    const onBeforeInstall = (evt: Event) => {
      evt.preventDefault();
      deferredRef.current = evt as BeforeInstallPromptEvent;
    };
    const onInstalled = () => {
      deferredRef.current = null;
      dismissToast(TOAST_ID);
      write(DISMISSED_KEY, String(Date.now()));
    };
    window.addEventListener('beforeinstallprompt', onBeforeInstall);
    window.addEventListener('appinstalled', onInstalled);

    const visits = countVisit();
    const timer = setTimeout(() => {
      const show = shouldShowInstallHint({
        isTauri: false,
        isStandalone: isStandalone(),
        visits,
        dismissedAt: readNumber(DISMISSED_KEY),
        now: Date.now(),
      });
      if (!show) return;
      const kind = installHintKind(deferredRef.current !== null, isIosSafari());
      if (kind === 'none') return;

      const dismiss = () => {
        write(DISMISSED_KEY, String(Date.now()));
        dismissToast(TOAST_ID);
      };

      enqueueToast({
        id: TOAST_ID,
        iconSrc: Icons.Download,
        displayName: 'Install Lotus Chat',
        body:
          kind === 'prompt'
            ? 'Add it to your home screen or desktop for faster access and its own window. Tap to install.'
            : 'On iPhone/iPad: tap Share, then "Add to Home Screen". Tap to dismiss.',
        roomName: '',
        roomId: '',
        sticky: true,
        onDismiss: () => write(DISMISSED_KEY, String(Date.now())),
        onClick: () => {
          const deferred = deferredRef.current;
          if (kind === 'prompt' && deferred) {
            deferred
              .prompt()
              .then(() => deferred.userChoice)
              .then(({ outcome }) => {
                if (outcome === 'accepted') deferredRef.current = null;
              })
              .catch(() => undefined)
              .finally(dismiss);
            return;
          }
          dismiss();
        },
      });
    }, DECIDE_DELAY_MS);

    return () => {
      clearTimeout(timer);
      window.removeEventListener('beforeinstallprompt', onBeforeInstall);
      window.removeEventListener('appinstalled', onInstalled);
    };
  }, [enqueueToast, dismissToast]);
}