import { useEffect, useMemo, useRef } from 'react';
import { useNavigate } from 'react-router-dom';
import { useCurrentUser } from '@/hooks/useCurrentUser';
import { useActivityNotifications, type ActivityNotification } from '@/hooks/useActivityNotifications';
import { useCrewNotifications } from '@/hooks/useCrewNotifications';
import { useNewsletterIssues } from '@/hooks/useNewsletterIssues';
import { useNewsletterSubscription } from '@/hooks/useNewsletterSubscription';
import { useDmEnvelopes, type DmEnvelope } from '@/hooks/useDmEnvelopes';
import { useNotificationPrefs } from '@/hooks/useNotificationPrefs';
import { useLocalReminders } from '@/hooks/useLocalReminders';
import { isNativePlatform } from '@/lib/platform';
import {
  getNotificationPermission,
  listenForNotificationTaps,
  showOsNotification,
} from '@/lib/osNotify';
import type { NotificationCategory, NotificationPrefs } from '@/lib/notificationPrefs';
import type { CollectiveJoinRequest, CrewInvite, CrewJoinRequest, SkateCrew, SkateNewsletterIssue } from '@/lib/types';

/**
 * Turns the in-app activity the app already computes (bell, crews, DMs,
 * newsletter) into OS notifications — **without adding any new relay traffic or
 * any new network destination**.
 *
 * Design constraints, all deliberate:
 *  - **Opt-in only.** The engine is not even mounted until the user enables
 *    notifications, and nothing is requested from the OS until then.
 *  - **Never decrypts.** DM notifications come from the encrypted gift-wrap
 *    ENVELOPE, so an Amber user is never prompted to decrypt just to be told
 *    they have a message.
 *  - **No history replay.** Each source is "primed" silently the first time it
 *    returns data; only items that arrive afterwards are ever announced.
 *  - **Only when you're not looking.** A notification is suppressed while the
 *    app/tab is visible — the bell already covers that case.
 *
 * Delivery is best-effort and local: a closed app/browser is not reachable
 * without a server-side push, which this intentionally is not.
 */

type Source = NotificationCategory;

interface Candidate {
  /** Stable identity — event/wrap id, prefixed by kind. */
  key: string;
  source: Source;
  createdAt: number;
  title: string;
  body: string;
  path: string;
}

interface SeenState {
  primed: Partial<Record<Source, boolean>>;
  ids: string[];
}

const SEEN_KEY = 'skatespots:notifications:seen';
const MAX_SEEN_IDS = 600;
const MAX_PER_BURST = 3;

function loadSeen(): SeenState {
  try {
    const raw = localStorage.getItem(SEEN_KEY);
    if (raw) {
      const parsed = JSON.parse(raw) as SeenState;
      if (Array.isArray(parsed?.ids)) {
        return { primed: parsed.primed ?? {}, ids: parsed.ids };
      }
    }
  } catch {
    // Corrupt/blocked storage — start fresh.
  }
  return { primed: {}, ids: [] };
}

function persistSeen(state: SeenState): void {
  try {
    localStorage.setItem(
      SEEN_KEY,
      JSON.stringify({ primed: state.primed, ids: state.ids.slice(-MAX_SEEN_IDS) }),
    );
  } catch {
    // Storage full/blocked — notifications still work for this session.
  }
}

/** `/crew/<pubkey>/<identifier>` from a `35006:pubkey:identifier` coordinate. */
function coordPath(coord: string, route: string, fallback: string): string {
  const parts = coord.split(':');
  if (parts.length >= 3 && parts[1] && parts[2]) return `/${route}/${parts[1]}/${parts[2]}`;
  return fallback;
}

function activityCandidate(n: ActivityNotification): Candidate {
  let title: string;
  switch (n.type) {
    case 'zap':
      title = n.amountSats ? `You got zapped ${n.amountSats.toLocaleString()} sats` : 'You got zapped';
      break;
    case 'reaction':
      title = 'Someone liked your post';
      break;
    case 'repost':
      title = 'Someone reposted you';
      break;
    case 'mention':
      title = 'Someone mentioned you';
      break;
    case 'reply':
      title = 'Someone replied to you';
      break;
    case 'rsvp':
      title = "Someone RSVP'd to your event";
      break;
    case 'event-update':
      title = "An event you're going to was updated";
      break;
    default:
      title = 'New activity';
      break;
  }
  return {
    key: `activity:${n.id}`,
    source: 'social',
    createdAt: n.createdAt,
    title,
    body: 'Tap to open SkateSpots',
    path: '/',
  };
}

function buildCrewCandidates(
  invites: CrewInvite[],
  listedCrews: SkateCrew[],
  joinRequests: Array<{ request: CrewJoinRequest }>,
  collectiveRequests: CollectiveJoinRequest[],
): Candidate[] {
  const out: Candidate[] = [];
  for (const inv of invites) {
    out.push({
      key: `crew-invite:${inv.id}`,
      source: 'crew',
      createdAt: inv.createdAt,
      title: 'Crew invite',
      body: `You're invited to ${inv.crewName}`,
      path: coordPath(inv.crewCoord, 'crew', '/crews'),
    });
  }
  for (const crew of listedCrews) {
    out.push({
      key: `crew-confirm:${crew.pubkey}:${crew.identifier}`,
      source: 'crew',
      createdAt: crew.createdAt ?? 0,
      title: "You've been added to a crew",
      body: `${crew.name} — confirm to join`,
      path: `/crew/${crew.pubkey}/${crew.identifier}`,
    });
  }
  for (const { request } of joinRequests) {
    out.push({
      key: `crew-join:${request.id}`,
      source: 'crew',
      createdAt: request.createdAt,
      title: 'Join request',
      body: `Someone wants to join ${request.crewName}`,
      path: coordPath(request.crewCoord, 'crew', '/crews'),
    });
  }
  for (const req of collectiveRequests) {
    out.push({
      key: `crew-collective:${req.id}`,
      source: 'crew',
      createdAt: req.createdAt,
      title: 'Join request',
      body: `Someone wants to join ${req.collectiveName}`,
      path: '/crews',
    });
  }
  return out;
}

function dmCandidate(envelope: DmEnvelope): Candidate {
  return {
    key: `dm:${envelope.id}`,
    source: 'dms',
    createdAt: envelope.createdAt,
    title: 'New direct message',
    body: 'Tap to read it',
    path: '/messages',
  };
}

function newsletterCandidate(issue: SkateNewsletterIssue): Candidate {
  return {
    key: `newsletter:${issue.id}`,
    source: 'newsletter',
    createdAt: issue.publishedAt,
    title: issue.title,
    body: 'New SkateSpots drop',
    path: '/newsletter',
  };
}

async function dispatchNotifications(items: Candidate[]): Promise<void> {
  const permission = await getNotificationPermission();
  if (permission !== 'granted') return;

  const sorted = [...items].sort((a, b) => b.createdAt - a.createdAt);
  const shown = sorted.slice(0, MAX_PER_BURST);
  for (const candidate of shown) {
    await showOsNotification({
      id: candidate.key,
      title: candidate.title,
      body: candidate.body,
      path: candidate.path,
    });
  }
  if (sorted.length > shown.length) {
    await showOsNotification({
      id: `summary:${Date.now()}`,
      title: `${sorted.length - shown.length} more updates`,
      body: 'Open SkateSpots to catch up',
      path: '/',
    });
  }
}

/**
 * Mounted once in `Layout`. Renders nothing; the inner engine only exists once
 * notifications are enabled, so disabling them costs zero queries.
 */
export function OsNotificationBridge() {
  const { user } = useCurrentUser();
  const [prefs] = useNotificationPrefs();

  if (!user || !prefs.enabled) return null;
  return <NotificationEngine prefs={prefs} />;
}

function NotificationEngine({ prefs }: { prefs: NotificationPrefs }) {
  const navigate = useNavigate();
  const { notifications: activity, isLoading: activityLoading } = useActivityNotifications();
  const { invites, listedCrews, joinRequests, collectiveRequests, isLoading: crewLoading } =
    useCrewNotifications();
  const { data: issues = [], isLoading: newsletterLoading } = useNewsletterIssues();
  const { isSubscribed } = useNewsletterSubscription();
  const { data: envelopes = [], isFetched: dmFetched } = useDmEnvelopes(true);

  // Loaded lazily and mutated directly (never state) so bookkeeping can't cause
  // a render loop.
  const seenRef = useRef<SeenState | null>(null);
  if (seenRef.current === null) seenRef.current = loadSeen();

  // Native notification taps → in-app navigation. No-op on the web.
  useEffect(() => {
    let unsubscribe: (() => void) | undefined;
    let cancelled = false;
    void listenForNotificationTaps((path) => navigate(path)).then((fn) => {
      if (cancelled) fn();
      else unsubscribe = fn;
    });
    return () => {
      cancelled = true;
      unsubscribe?.();
    };
  }, [navigate]);

  const socialItems = useMemo(() => activity.map(activityCandidate), [activity]);
  const crewItems = useMemo(
    () => buildCrewCandidates(invites, listedCrews, joinRequests, collectiveRequests),
    [invites, listedCrews, joinRequests, collectiveRequests],
  );
  const newsletterItems = useMemo(
    () => (isSubscribed ? issues.map(newsletterCandidate) : []),
    [issues, isSubscribed],
  );
  const dmItems = useMemo(() => envelopes.map(dmCandidate), [envelopes]);

  useEffect(() => {
    const seen = seenRef.current;
    if (!seen) return;

    const sources: Array<{ name: Source; ready: boolean; items: Candidate[] }> = [
      { name: 'social', ready: !activityLoading, items: socialItems },
      { name: 'crew', ready: !crewLoading, items: crewItems },
      { name: 'newsletter', ready: !newsletterLoading, items: newsletterItems },
      { name: 'dms', ready: dmFetched, items: dmItems },
    ];

    let changed = false;
    const fresh: Candidate[] = [];

    for (const source of sources) {
      // Wait for this source's first real result — priming on an empty default
      // would make the eventual data look "new" and flood the shade.
      if (!source.ready) continue;

      if (!seen.primed[source.name]) {
        seen.primed[source.name] = true;
        for (const item of source.items) seen.ids.push(item.key);
        changed = true;
        continue;
      }

      const seenSet = new Set(seen.ids);
      for (const item of source.items) {
        if (seenSet.has(item.key)) continue;
        seenSet.add(item.key);
        seen.ids.push(item.key);
        fresh.push(item);
        changed = true;
      }
    }

    if (changed) persistSeen(seen);
    if (fresh.length === 0) return;

    // If the user is looking at the app, the bell already told them.
    if (typeof document !== 'undefined' && document.visibilityState === 'visible') return;

    const allowed = fresh.filter((item) => prefs[item.source]);
    if (allowed.length === 0) return;
    void dispatchNotifications(allowed);
  }, [
    socialItems,
    crewItems,
    newsletterItems,
    dmItems,
    activityLoading,
    crewLoading,
    newsletterLoading,
    dmFetched,
    prefs,
  ]);

  // Scheduled reminders are native-only (the web has no scheduler), so only
  // mount the hook — and therefore only run its event/RSVP queries — when the
  // platform can actually use them.
  return prefs.reminders && isNativePlatform() ? <LocalReminders /> : null;
}

function LocalReminders() {
  useLocalReminders();
  return null;
}