import { useEffect, useState } from 'react';
import { atom } from 'jotai';
import { ClientEvent, MatrixClient, SyncState } from 'matrix-js-sdk';

/**
 * [Gitea #317] A hung homeserver (accepts connections, never answers) went
 * unnoticed for up to 110 s: the SDK only gives up on a /sync long-poll after
 * pollTimeout (30 s) + an 80 s buffer, and until then the sync state stays
 * SYNCING, so no strip showed and Kuma wasn't asked. This watchdog notices a
 * /sync that's overdue and confirms with a short probe of /versions.
 */
export const STALL_AFTER_MS = 45_000; // a healthy long-poll returns within ~30 s
const CHECK_EVERY_MS = 10_000;
const PROBE_TIMEOUT_MS = 5_000;

export const homeserverStalledAtom = atom(false);

/** Pure: should we probe, given the last sync response time? */
export const syncOverdue = (lastSyncAt: number, now: number, state: SyncState | null): boolean =>
  state === SyncState.Syncing && now - lastSyncAt > STALL_AFTER_MS;

export function useHomeserverStall(mx: MatrixClient): boolean {
  const [stalled, setStalled] = useState(false);
  useEffect(() => {
    let lastSyncAt = Date.now();
    let probing = false;
    const onSync = () => {
      lastSyncAt = Date.now();
      setStalled(false);
    };
    const check = async () => {
      if (probing || !syncOverdue(lastSyncAt, Date.now(), mx.getSyncState())) return;
      probing = true;
      let answered = false;
      try {
        const res = await fetch(`${mx.getHomeserverUrl()}/_matrix/client/versions`, {
          cache: 'no-store',
          signal: AbortSignal.timeout(PROBE_TIMEOUT_MS),
        });
        answered = res.ok;
      } catch {
        answered = false;
      }
      probing = false;
      // Still overdue and the server didn't answer a trivial request: stalled.
      if (!answered && syncOverdue(lastSyncAt, Date.now(), mx.getSyncState())) setStalled(true);
      if (answered) setStalled(false);
    };
    mx.on(ClientEvent.Sync, onSync);
    const id = setInterval(check, CHECK_EVERY_MS);
    return () => {
      mx.removeListener(ClientEvent.Sync, onSync);
      clearInterval(id);
    };
  }, [mx]);
  return stalled;
}