SkateSpots/src/hooks/useCoordinator.ts

import { useCallback, useMemo, useState } from 'react';
import { useNostr } from '@nostrify/react';
import { useLocalStorage } from '@/hooks/useLocalStorage';
import {
  COORDINATOR_STORAGE_KEY,
  CORDN_RELAY_URL,
  coordinatorNameFromEvent,
  type CoordinatorConfig,
} from '@/lib/coordinator';

/** The user's chosen Cordn coordinator, persisted device-locally. */
export function useCoordinator() {
  const [stored, setStored] = useLocalStorage<CoordinatorConfig | null>(
    COORDINATOR_STORAGE_KEY,
    null,
  );

  const coordinator = stored && stored.pubkey ? stored : null;

  const setCoordinator = useCallback(
    (config: Omit<CoordinatorConfig, 'addedAt'>) => {
      setStored({
        pubkey: config.pubkey,
        relays: config.relays,
        addedAt: Date.now(),
      });
    },
    [setStored],
  );

  const removeCoordinator = useCallback(() => setStored(null), [setStored]);

  return { coordinator, setCoordinator, removeCoordinator };
}

export type CoordinatorHealthStatus =
  | 'idle'
  | 'checking'
  | 'online'
  | 'stale'
  | 'offline'
  | 'error';

export interface CoordinatorHealth {
  status: CoordinatorHealthStatus;
  /** Unix seconds of the newest event authored by the coordinator. */
  lastSeen: number | null;
  eventCount: number;
  /** Display name parsed from the announcement, when we can find one. */
  name: string | null;
  error: string | null;
  checkedAt: number | null;
  /** Actual ContextVM RPC probe, not just presence. */
  rpcStatus: 'idle' | 'checking' | 'ok' | 'error';
  rpcLatencyMs: number | null;
  rpcError: string | null;
}

/**
 * Same freshness rule as the CVM server probe: ContextVM servers re-announce on
 * a heartbeat, so allow a few missed beats before calling it stale.
 */
const STALE_AFTER_MS = 45 * 60 * 1000;

const INITIAL: CoordinatorHealth = {
  status: 'idle',
  lastSeen: null,
  eventCount: 0,
  name: null,
  error: null,
  checkedAt: null,
  rpcStatus: 'idle',
  rpcLatencyMs: null,
  rpcError: null,
};

function randomKeyHex(): string {
  const bytes = new Uint8Array(32);
  if (globalThis.crypto?.getRandomValues) {
    globalThis.crypto.getRandomValues(bytes);
  } else {
    for (let i = 0; i < bytes.length; i += 1) bytes[i] = Math.floor(Math.random() * 256);
  }
  return Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
}

async function probeCoordinatorRpc(
  coordinator: CoordinatorConfig,
  relays: string[],
): Promise<Pick<CoordinatorHealth, 'rpcStatus' | 'rpcLatencyMs' | 'rpcError'>> {
  let client: { listAvailableKeyPackages: () => Promise<unknown>; disconnect: () => Promise<void> } | null = null;
  const started = Date.now();
  try {
    const { CordnCoordinatorClient } = await import('@/lib/cordn/native/coordinator');
    client = new CordnCoordinatorClient({
      serverPubkey: coordinator.pubkey,
      relays,
      privateKeyHex: randomKeyHex(),
    });
    await Promise.race([
      client.listAvailableKeyPackages(),
      new Promise<never>((_, reject) =>
        setTimeout(() => reject(new Error('Coordinator RPC timed out.')), 7_000),
      ),
    ]);
    return { rpcStatus: 'ok', rpcLatencyMs: Date.now() - started, rpcError: null };
  } catch (e) {
    return {
      rpcStatus: 'error',
      rpcLatencyMs: null,
      rpcError: e instanceof Error ? e.message : 'Coordinator RPC failed.',
    };
  } finally {
    if (client) await client.disconnect().catch(() => undefined);
  }
}

/**
 * Presence probe for a coordinator.
 *
 * A Cordn coordinator is a ContextVM server, so "is it alive?" is answerable
 * without speaking Cordn's RPC: query the relays it advertises for events it
 * authored (its announcement + heartbeat). A private/unannounced coordinator
 * legitimately shows nothing here — the copy says so rather than alarming.
 */
export function useCoordinatorHealth(coordinator: CoordinatorConfig | null) {
  const { nostr } = useNostr();
  const [result, setResult] = useState<CoordinatorHealth>(INITIAL);

  const relays = useMemo(
    () => (coordinator?.relays.length ? coordinator.relays : [CORDN_RELAY_URL]),
    [coordinator],
  );

  const check = useCallback(async () => {
    if (!coordinator) return;
    setResult((r) => ({
      ...r,
      status: 'checking',
      error: null,
      rpcStatus: 'checking',
      rpcLatencyMs: null,
      rpcError: null,
    }));

    const rpc = await probeCoordinatorRpc(coordinator, relays);

    try {
      const signal = AbortSignal.timeout(8000);
      const batches = await Promise.all(
        relays.map(async (url) => {
          try {
            return await nostr.relay(url).query(
              [{ authors: [coordinator.pubkey], limit: 25 }],
              { signal },
            );
          } catch {
            // One relay failing must not stop the probe.
            return [];
          }
        }),
      );

      const events = batches.flat();
      if (events.length === 0) {
        setResult({
          status: 'offline',
          lastSeen: null,
          eventCount: 0,
          name: null,
          error: null,
          checkedAt: Date.now(),
          ...rpc,
        });
        return;
      }

      const newest = events.reduce((a, b) => (b.created_at > a.created_at ? b : a));
      const ageMs = Date.now() - newest.created_at * 1000;

      setResult({
        status: ageMs <= STALE_AFTER_MS ? 'online' : 'stale',
        lastSeen: newest.created_at,
        eventCount: events.length,
        name: coordinatorNameFromEvent(newest),
        error: null,
        checkedAt: Date.now(),
        ...rpc,
      });
    } catch (err) {
      setResult({
        status: 'error',
        lastSeen: null,
        eventCount: 0,
        name: null,
        error: err instanceof Error ? err.message : 'Could not reach the relays',
        checkedAt: Date.now(),
        ...rpc,
      });
    }
  }, [coordinator, relays, nostr]);

  return { ...result, check };
}