import type { CollabTokenResponse } from '@dorfteich/shared';
import { HocuspocusProvider } from '@hocuspocus/provider';
import { useCallback, useEffect, useRef, useState } from 'react';
import { IndexeddbPersistence } from 'y-indexeddb';
import * as Y from 'yjs';

import { ApiError, apiGet } from '../lib/api';

/** What the editor shows about the live connection (issue #36). */
export type ConnectionStatus = 'connecting' | 'connected' | 'reconnecting' | 'offline';

export interface CollabState {
  provider: HocuspocusProvider | null;
  status: ConnectionStatus;
  /** Access level of the current token; `ro` clients cannot edit. */
  mode: 'rw' | 'ro' | null;
  /** Set once the server rejects an update for exceeding the size ceiling (#35). */
  tooLarge: boolean;
  /** True when there are edits held only on this device (offline, #38). */
  localOnly: boolean;
  /**
   * Set when the api refuses a collaboration token (403/404) on (re)connect,
   * i.e. edit access was revoked (issue #39). The local content stays visible
   * so the user can export it; live sync stops.
   */
  accessRevoked: boolean;
  /** Discard the device-local copy of this page (clears IndexedDB, #39). */
  discardLocal: () => Promise<void>;
}

/** IndexedDB database name for a page's local Yjs persistence (issue #38). */
function localDbName(pageId: string): string {
  return `dorfteich-page-${pageId}`;
}

/** WebSocket endpoint of the collab server, behind the same origin as the app
 * (the reverse proxy forwards `/collab`; deployment.md requires WS upgrade). */
function collabWsUrl(): string {
  const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
  return `${protocol}//${window.location.host}/collab`;
}

/**
 * Binds a page's `Y.Doc` to the Hocuspocus collaboration server (ADR 0003,
 * realtime-collaboration.md). The document loads and persists through the
 * collab server now — there is no REST autosave. The collaboration token is
 * fetched lazily on every (re)connect, so an expired token is replaced
 * transparently and a permission change takes effect on the next reconnect.
 */
export function useCollabProvider(ydoc: Y.Doc | null, pageId: string): CollabState {
  const [provider, setProvider] = useState<HocuspocusProvider | null>(null);
  const [wsStatus, setWsStatus] = useState<'connecting' | 'connected' | 'disconnected'>(
    'connecting',
  );
  const [synced, setSynced] = useState(false);
  const [everConnected, setEverConnected] = useState(false);
  const [online, setOnline] = useState(() => navigator.onLine);
  const [mode, setMode] = useState<'rw' | 'ro' | null>(null);
  const [tooLarge, setTooLarge] = useState(false);
  const [hasUnsynced, setHasUnsynced] = useState(false);
  const [accessRevoked, setAccessRevoked] = useState(false);
  // Held so `discardLocal` can clear the current page's IndexedDB store even
  // after `accessRevoked` has stopped live sync (issue #39).
  const localPersistenceRef = useRef<IndexeddbPersistence | null>(null);

  useEffect(() => {
    if (!ydoc) return;
    let disposed = false;
    // Whether the server has ever confirmed our state this session; decides
    // whether the local copy is discarded on leave (below).
    let serverSynced = false;

    // Local-first persistence: every opened page is mirrored to IndexedDB so
    // edits survive a reload and offline work (ADR 0003, #38). The provider
    // and IndexedDB share the same Y.Doc and merge conflict-free.
    const localPersistence = new IndexeddbPersistence(localDbName(pageId), ydoc);
    localPersistenceRef.current = localPersistence;
    setAccessRevoked(false);

    const instance = new HocuspocusProvider({
      url: collabWsUrl(),
      name: pageId,
      document: ydoc,
      token: async () => {
        try {
          const response = await apiGet<CollabTokenResponse>(`/pages/${pageId}/collab-token`);
          if (!disposed) {
            setMode(response.mode);
            setAccessRevoked(false);
          }
          return response.token;
        } catch (error) {
          // A refused token (403/404) means edit access was revoked while we
          // were connected or offline (#39). Surface it so the editor can offer
          // an export; the effect below then stops the reconnect loop. Rethrow
          // so this connection attempt aborts rather than using a stale token.
          if (error instanceof ApiError && (error.status === 403 || error.status === 404)) {
            if (!disposed) setAccessRevoked(true);
          }
          throw error;
        }
      },
      onStatus: ({ status }) => {
        if (disposed) return;
        setWsStatus(status);
        if (status === 'connected') setEverConnected(true);
      },
      onSynced: () => {
        serverSynced = true;
        if (!disposed) setSynced(true);
      },
      onDisconnect: () => {
        if (!disposed) setSynced(false);
      },
      onUnsyncedChanges: ({ number }) => {
        if (!disposed) setHasUnsynced(number > 0);
      },
      onStateless: ({ payload }) => {
        if (disposed) return;
        try {
          const message = JSON.parse(payload) as { type?: string; code?: string };
          if (message.type === 'error' && message.code === 'page_document_too_large') {
            setTooLarge(true);
          }
        } catch {
          // Ignore malformed stateless payloads.
        }
      },
    });
    setProvider(instance);

    return () => {
      disposed = true;
      instance.destroy();
      // Discard the local copy once the server has our changes (bounds
      // IndexedDB growth); otherwise keep it so offline edits survive to the
      // next visit (realtime-collaboration.md §Offline).
      if (serverSynced) {
        void localPersistence.clearData();
      } else {
        void localPersistence.destroy();
      }
      if (localPersistenceRef.current === localPersistence) localPersistenceRef.current = null;
      setProvider(null);
      setSynced(false);
      setHasUnsynced(false);
    };
  }, [ydoc, pageId]);

  // Once access is revoked, stop the reconnect loop: every reconnect would only
  // fetch another refused token and hammer the api (issue #39). The local copy
  // stays intact for export until the user leaves or explicitly discards it.
  useEffect(() => {
    if (accessRevoked && provider) provider.disconnect();
  }, [accessRevoked, provider]);

  useEffect(() => {
    const goOnline = (): void => setOnline(true);
    const goOffline = (): void => setOnline(false);
    window.addEventListener('online', goOnline);
    window.addEventListener('offline', goOffline);
    return () => {
      window.removeEventListener('online', goOnline);
      window.removeEventListener('offline', goOffline);
    };
  }, []);

  let status: ConnectionStatus;
  if (!online) {
    status = 'offline';
  } else if (wsStatus === 'connected' && synced) {
    status = 'connected';
  } else if (everConnected) {
    status = 'reconnecting';
  } else {
    status = 'connecting';
  }

  // Local-only = we hold edits the server has not acknowledged and we are not
  // currently in sync (offline or reconnecting).
  const localOnly = hasUnsynced && status !== 'connected';

  const discardLocal = useCallback(async (): Promise<void> => {
    await localPersistenceRef.current?.clearData();
  }, []);

  return { provider, status, mode, tooLarge, localOnly, accessRevoked, discardLocal };
}