import { useCallback, useEffect, useMemo, useRef } from 'react';
import { useNostrLogin } from '@nostrify/react/login';
import { useLocalStorage } from '@/hooks/useLocalStorage';
import { useCurrentUser } from '@/hooks/useCurrentUser';
import { useSyncedAppData, type MergeStrategy } from '@/hooks/useSyncedAppData';
import { isInteractiveSigner } from '@/lib/signerCapabilities';

/**
 * useReadState — cross-device "what have I already seen" markers.
 *
 * SkateSpots tracks read state for four surfaces (the notification bell, DMs,
 * crew chats, the newsletter). Historically each lived in localStorage keyed by
 * pubkey, so clearing the bell on your phone left the laptop's badge lit. This
 * hook keeps that instant, offline-first localStorage behavior AND mirrors the
 * markers into one encrypted `kind-30078` event so they follow your npub across
 * devices.
 *
 * DESIGN
 * ──────
 * - **localStorage stays the fast path / source of truth for the UI.** Reads are
 *   synchronous and work while logged out. The individual read hooks
 *   (`useNotificationsRead`, `useDMRead`, …) keep their exact public API and
 *   simply call this to stay in sync — no consumer component changes.
 * - **The synced copy is the cross-device layer.** On login we hydrate from the
 *   relay (merging in anything newer) and every `mark*` also patches the synced
 *   event (debounced).
 * - **Merge = MAX per field.** Read markers only ever move forward in time, so
 *   merging two devices is "take the larger timestamp" — commutative and safe,
 *   never clobbers.
 */

/** The whole synced read-state blob. All values are unix seconds. */
export interface ReadState {
  /** Notification center last-opened. */
  notifications: number;
  /** Badge-dismiss marker for actionable items (invites, join requests). */
  notificationsSeen: number;
  /** Newsletter mailbox last-read. */
  newsletter: number;
  /** DM last-read, keyed by the other party's lowercased pubkey. */
  dms: Record<string, number>;
  /** Crew chat last-seen, keyed by crew coordinate. */
  crewChats: Record<string, number>;
}

const EMPTY: ReadState = {
  notifications: 0,
  notificationsSeen: 0,
  newsletter: 0,
  dms: {},
  crewChats: {},
};

const D_TAG = 'skatespots:read-state';

/** Take the larger of two unix-second markers (0 = never). */
const maxTs = (a = 0, b = 0) => (a > b ? a : b);

/** Field-wise max-merge: never moves a marker backwards, never drops a key. */
const mergeReadState: MergeStrategy<ReadState> = (remote, patch) => {
  const dms: Record<string, number> = { ...remote.dms };
  for (const [k, v] of Object.entries(patch.dms)) dms[k] = maxTs(dms[k], v);

  const crewChats: Record<string, number> = { ...remote.crewChats };
  for (const [k, v] of Object.entries(patch.crewChats)) {
    crewChats[k] = maxTs(crewChats[k], v);
  }

  return {
    notifications: maxTs(remote.notifications, patch.notifications),
    notificationsSeen: maxTs(remote.notificationsSeen, patch.notificationsSeen),
    newsletter: maxTs(remote.newsletter, patch.newsletter),
    dms,
    crewChats,
  };
};

/** Merge a synced blob into the local one (used when the relay copy arrives). */
function mergeIntoLocal(local: ReadState, incoming: ReadState): ReadState {
  return mergeReadState(local, incoming);
}

/**
 * Shared read-state store. Prefer the specific hooks below in components; this
 * is the single place that owns the localStorage blob + the synced mirror.
 */
export function useReadState() {
  const { user } = useCurrentUser();
  const { logins } = useNostrLogin();
  const lsKey = user ? `skatespots:read-state:${user.pubkey}` : 'skatespots:read-state:anon';
  const [local, setLocal] = useLocalStorage<ReadState>(lsKey, EMPTY);

  // Amber (NIP-55) prompts on every nip44 encrypt AND every sign. Marking the
  // bell (or a DM) read is not a signing action, so for an interactive signer we
  // keep the marker LOCAL-ONLY and never publish — no surprise popups just for
  // glancing at notifications. Non-interactive signers (nsec, extension) still
  // mirror the markers to the encrypted kind-30078 event for cross-device sync.
  const interactive = useMemo(() => isInteractiveSigner(user, logins), [user, logins]);

  const synced = useSyncedAppData<ReadState>({
    dTag: D_TAG,
    alt: 'SkateSpots read-state (encrypted)',
    empty: EMPTY,
    merge: mergeReadState,
  });

  // When the relay copy arrives (or changes), fold anything newer into local so
  // a device that was behind catches up. Max-merge means this can only advance
  // markers, never undo a local "mark read".
  const remote = synced.data;
  useEffect(() => {
    if (!remote) return;
    setLocal((prev) => {
      const merged = mergeIntoLocal(prev, remote);
      // Avoid a needless state churn if nothing actually changed.
      return JSON.stringify(merged) === JSON.stringify(prev) ? prev : merged;
    });
  }, [remote, setLocal]);

  // Hold the synced engine + interactive flag in refs so `apply` can be a
  // STABLE callback. Depending on them directly made `apply` (and every mark*
  // derived from it) change identity on every render, which made effects such as
  // NewsletterPage's / the notification bell's run after every render and —
  // because marking read set a new state object — loop until React aborted with
  // "Maximum update depth exceeded".
  const syncedRef = useRef(synced);
  syncedRef.current = synced;
  const interactiveRef = useRef(interactive);
  interactiveRef.current = interactive;

  /** Apply a patch to BOTH the instant local blob and the synced mirror. */
  const apply = useCallback(
    (producePatch: (current: ReadState) => ReadState) => {
      setLocal((prev) => producePatch(prev));
      // Interactive signer: local-only (see `interactive` above) — publishing
      // here would pop Amber just for reading. Otherwise mirror to the synced
      // event (no-op for anon; debounced + merged inside).
      if (interactiveRef.current) return;
      void syncedRef.current.patch((current) => producePatch(current));
    },
    [setLocal],
  );

  return { state: local, apply };
}

// ─── Backwards-compatible, drop-in replacements for the old hooks ────────────
// These preserve the EXACT signatures the components already consume, so no
// call site changes — only the storage underneath gains cross-device sync.

/** @see useNotificationsRead (legacy name kept) */
export function useNotificationsRead() {
  const { state, apply } = useReadState();

  const markAllRead = useCallback(() => {
    const now = Math.floor(Date.now() / 1000);
    // Idempotent: return the SAME object when nothing actually moves, so React
    // bails out instead of re-rendering (and re-running any effect that calls
    // this). A fresh object every call was the other half of the render loop.
    apply((s) =>
      s.notifications >= now && s.notificationsSeen >= now
        ? s
        : { ...s, notifications: now, notificationsSeen: now },
    );
  }, [apply]);

  return { lastRead: state.notifications, seenAt: state.notificationsSeen, markAllRead };
}

/** @see useNewsletterRead */
export function useNewsletterRead() {
  const { state, apply } = useReadState();

  const markNewsletterRead = useCallback(() => {
    const now = Math.floor(Date.now() / 1000);
    // Idempotent (see markAllRead) — bail with the same object if already marked.
    apply((s) => (s.newsletter >= now ? s : { ...s, newsletter: now }));
  }, [apply]);

  return { lastRead: state.newsletter, markNewsletterRead };
}

/** @see useDMRead */
export function useDMRead() {
  const { state, apply } = useReadState();

  const markRead = useCallback(
    (conversationWith: string, ts?: number) => {
      const at = ts ?? Math.floor(Date.now() / 1000);
      const key = conversationWith.toLowerCase();
      apply((s) => {
        if ((s.dms[key] ?? 0) >= at) return s; // never backwards
        return { ...s, dms: { ...s.dms, [key]: at } };
      });
    },
    [apply],
  );

  const getLastRead = useCallback(
    (conversationWith: string) => state.dms[conversationWith.toLowerCase()] ?? 0,
    [state.dms],
  );

  return { lastReadMap: state.dms, markRead, getLastRead };
}

/** @see useCrewChatRead */
export function useCrewChatRead(crewCoord: string | undefined) {
  const { state, apply } = useReadState();

  const lastSeen = useMemo(
    () => (crewCoord ? state.crewChats[crewCoord] ?? 0 : 0),
    [state.crewChats, crewCoord],
  );

  const markSeen = useCallback(
    (ts?: number) => {
      if (!crewCoord) return;
      const at = ts ?? Math.floor(Date.now() / 1000);
      apply((s) => {
        if ((s.crewChats[crewCoord] ?? 0) >= at) return s;
        return { ...s, crewChats: { ...s.crewChats, [crewCoord]: at } };
      });
    },
    [apply, crewCoord],
  );

  return { lastSeen, markSeen };
}