import { useSetAtom } from 'jotai';
import { useEffect } from 'react';
import {
  ClientEvent,
  ClientEventHandlerMap,
  ConnectionError,
  EventStatus,
  KnownMembership,
  MatrixClient,
  MatrixError,
  MatrixEvent,
  Room,
  RoomEvent,
  RoomEventHandlerMap,
  SyncState,
} from 'matrix-js-sdk';
import { useMatrixClient } from '../../hooks/useMatrixClient';
import { sendOfflineAtom } from '../../state/sendOffline';
import {
  OUTBOX_MAX_AUTO_RETRIES,
  OutboxEntry,
  isRetryableSendError,
  loadOutbox,
  outboxRetryDelayMs,
  planRestore,
  saveOutbox,
  shouldKeepInOutbox,
  withEntry,
  withoutEntry,
} from '../../utils/outbox';

const PENDING: ReadonlySet<EventStatus | null> = new Set([
  EventStatus.SENDING,
  EventStatus.ENCRYPTING,
  EventStatus.QUEUED,
  EventStatus.NOT_SENT,
]);
const ONLINE: ReadonlySet<SyncState | null> = new Set([
  SyncState.Prepared,
  SyncState.Syncing,
  SyncState.Catchup,
]);
const OFFLINE: ReadonlySet<SyncState | null> = new Set([SyncState.Reconnecting, SyncState.Error]);

/** The server already has it: its transaction id came back down /sync. */
const isDelivered = (room: Room, txnId: string): boolean => {
  const hasTxn = (events: MatrixEvent[]) =>
    events.some((e) => e.getUnsigned().transaction_id === txnId);
  return (
    hasTxn(room.getLiveTimeline().getEvents()) ||
    room.getThreads().some((t) => hasTxn(t.liveTimeline.getEvents()))
  );
};

type OutboxSession = {
  /** Own pending events of this session, by txnId. */
  live: Map<string, { event: MatrixEvent; room: Room }>;
  autoRetries: Map<string, number>;
  restored: boolean;
  retrying: boolean;
};

// Per client, not per mount: a remount must neither restore twice nor forget
// the events it is tracking.
const sessions = new WeakMap<MatrixClient, OutboxSession>();
const getSession = (mx: MatrixClient): OutboxSession => {
  let session = sessions.get(mx);
  if (!session) {
    session = { live: new Map(), autoRetries: new Map(), restored: false, retrying: false };
    sessions.set(mx, session);
  }
  return session;
};

/**
 * [Gitea #112] Offline outbox (see utils/outbox.ts): mirrors own message sends
 * into localStorage until the server confirms them, puts unsent ones back
 * after a reload, and re-sends network failures when the connection returns.
 */
export function OutboxFeature() {
  const mx = useMatrixClient();
  const setOffline = useSetAtom(sendOfflineAtom);

  useEffect(() => {
    const userId = mx.getSafeUserId();
    let entries = loadOutbox(userId);
    const session = getSession(mx);
    const { live, autoRetries } = session;
    let disposed = false;
    let offlineNow = false;
    const timers = new Set<ReturnType<typeof setTimeout>>();

    const isOffline = () =>
      OFFLINE.has(mx.getSyncState()) ||
      (typeof navigator !== 'undefined' && navigator.onLine === false);

    const persist = (next: OutboxEntry[]) => {
      if (next === entries) return;
      entries = next;
      saveOutbox(userId, entries);
    };

    /**
     * A network failure while we think we're online (a blip neither sync nor
     * the browser noticed): try again shortly, backing off. Real outages are
     * handled by the reconnect / back-online triggers below.
     */
    const scheduleBlipRetry = (event: MatrixEvent) => {
      const attempts = autoRetries.get(event.getTxnId() ?? '') ?? 0;
      if (!isRetryableSendError(event.error) || attempts >= OUTBOX_MAX_AUTO_RETRIES || isOffline())
        return;
      const timer = setTimeout(() => {
        timers.delete(timer);
        retryQueued();
      }, outboxRetryDelayMs(attempts));
      timers.add(timer);
    };

    const onLocalEcho: RoomEventHandlerMap[RoomEvent.LocalEchoUpdated] = (event, room) => {
      const txnId = event.getTxnId();
      if (!txnId || event.getSender() !== userId) return;
      if (PENDING.has(event.status)) {
        if (!shouldKeepInOutbox(event.getType(), event.getContent())) return;
        live.set(txnId, { event, room });
        if (event.status === EventStatus.NOT_SENT) scheduleBlipRetry(event);
        persist(
          withEntry(entries, {
            txnId,
            roomId: room.roomId,
            threadId: event.threadRootId ?? null,
            type: event.getType(),
            content: event.getContent(),
            ts: event.getTs(),
          }),
        );
        return;
      }
      // SENT, CANCELLED, or the remote echo replaced it (status null).
      live.delete(txnId);
      autoRetries.delete(txnId);
      persist(withoutEntry(entries, txnId));
    };

    /** Re-send network failures, oldest first; a room stops at its first failure. */
    const retryQueued = async () => {
      if (session.retrying || disposed) return;
      session.retrying = true;
      try {
        const byRoom = new Map<Room, MatrixEvent[]>();
        Array.from(live.values())
          .filter(
            ({ event }) =>
              event.status === EventStatus.NOT_SENT &&
              isRetryableSendError(event.error) &&
              (autoRetries.get(event.getTxnId() ?? '') ?? 0) < OUTBOX_MAX_AUTO_RETRIES,
          )
          .sort((a, b) => a.event.getTs() - b.event.getTs())
          .forEach(({ event, room }) => {
            byRoom.set(room, [...(byRoom.get(room) ?? []), event]);
          });
        await Promise.all(
          Array.from(byRoom.entries()).map(async ([room, events]) => {
            for (const event of events) {
              if (disposed || event.status !== EventStatus.NOT_SENT) continue;
              const txnId = event.getTxnId() ?? '';
              autoRetries.set(txnId, (autoRetries.get(txnId) ?? 0) + 1);
              try {
                // eslint-disable-next-line no-await-in-loop
                await mx.resendEvent(event, room);
              } catch (e) {
                // Still offline: keep the rest of this room in order for the next try.
                if (isRetryableSendError(e)) break;
              }
            }
          }),
        );
      } finally {
        session.retrying = false;
      }
    };

    const restore = () => {
      if (session.restored) return;
      session.restored = true;
      const plan = planRestore(
        entries,
        Date.now(),
        (roomId) => mx.getRoom(roomId)?.getMyMembership() === KnownMembership.Join,
        (entry) => {
          const room = mx.getRoom(entry.roomId);
          return !!room && isDelivered(room, entry.txnId);
        },
      );
      plan.drop.forEach((entry) => persist(withoutEntry(entries, entry.txnId)));
      plan.restore.forEach((entry) => {
        const room = mx.getRoom(entry.roomId);
        if (!room || live.has(entry.txnId)) return;
        // Same shape as the SDK's own local echo (client.sendCompleteEvent).
        const event = new MatrixEvent({
          type: entry.type,
          content: entry.content,
          event_id: `~${entry.roomId}:${entry.txnId}`,
          sender: userId,
          room_id: entry.roomId,
          origin_server_ts: entry.ts,
        });
        const thread = entry.threadId ? room.getThread(entry.threadId) : undefined;
        if (thread) event.setThread(thread);
        event.setTxnId(entry.txnId);
        event.setStatus(EventStatus.NOT_SENT);
        if (plan.autoSend.has(entry.txnId)) {
          // Recent: treat like a send that lost the network (shown as Queued
          // while offline, re-sent below and on reconnect).
          // (The SDK types `error` as MatrixError but stores any send error there.)
          event.error = new ConnectionError(
            'not sent before the app was closed',
          ) as unknown as MatrixError;
        } else {
          // Old: back as "Failed to send"; the user decides (Retry / Cancel).
          autoRetries.set(entry.txnId, OUTBOX_MAX_AUTO_RETRIES);
        }
        try {
          room.addPendingEvent(event, entry.txnId); // emits LocalEchoUpdated → `live`
        } catch {
          // Already pending under this txnId: nothing to restore.
        }
      });
      if (!isOffline()) retryQueued();
    };

    const updateOffline = () => {
      const offline = isOffline();
      // Back online (sync recovered or the browser says so): send what's queued.
      if (offlineNow && !offline && session.restored) retryQueued();
      offlineNow = offline;
      setOffline(offline);
    };

    const onSync: ClientEventHandlerMap[ClientEvent.Sync] = (state, prevState) => {
      updateOffline();
      if (!ONLINE.has(state)) return;
      if (!session.restored) {
        restore();
        return;
      }
      if (OFFLINE.has(prevState) || prevState === SyncState.Catchup) retryQueued();
    };
    const onBrowserOnline = () => updateOffline();

    mx.on(RoomEvent.LocalEchoUpdated, onLocalEcho);
    mx.on(ClientEvent.Sync, onSync);
    window.addEventListener('online', onBrowserOnline);
    window.addEventListener('offline', onBrowserOnline);
    updateOffline();
    if (ONLINE.has(mx.getSyncState())) restore();

    return () => {
      disposed = true;
      timers.forEach((t) => clearTimeout(t));
      mx.off(RoomEvent.LocalEchoUpdated, onLocalEcho);
      mx.off(ClientEvent.Sync, onSync);
      window.removeEventListener('online', onBrowserOnline);
      window.removeEventListener('offline', onBrowserOnline);
    };
  }, [mx, setOffline]);

  return null;
}