Stirling-PDF/frontend/src/desktop/hooks/useBackendHealth.ts

import { useEffect, useState, useCallback } from 'react';
import { backendHealthMonitor } from '@app/services/backendHealthMonitor';
import { selfHostedServerMonitor } from '@app/services/selfHostedServerMonitor';
import { tauriBackendService } from '@app/services/tauriBackendService';
import { connectionModeService } from '@app/services/connectionModeService';
import type { BackendHealthState } from '@app/types/backendHealth';

/**
 * Hook to read backend health state for UI (Run button, BackendHealthIndicator).
 *
 * backendHealthMonitor tracks the local bundled backend.
 * selfHostedServerMonitor tracks the remote server in self-hosted mode.
 *
 * isOnline logic:
 * - SaaS mode: true when local backend is healthy
 * - Self-hosted mode (server online): true (remote is up)
 * - Self-hosted mode (server offline, local port known): true so the Run button
 *   stays enabled — operationRouter routes supported tools to local
 * - Self-hosted mode (server offline, local port unknown): false
 */
export function useBackendHealth() {
  const [health, setHealth] = useState<BackendHealthState>(() => backendHealthMonitor.getSnapshot());
  const [serverStatus, setServerStatus] = useState(
    () => selfHostedServerMonitor.getSnapshot().status
  );
  const [localUrl, setLocalUrl] = useState<string | null>(
    () => tauriBackendService.getBackendUrl()
  );
  const [connectionMode, setConnectionMode] = useState<string | null>(null);

  useEffect(() => {
    void connectionModeService.getCurrentMode().then(setConnectionMode);
  }, []);

  useEffect(() => {
    return backendHealthMonitor.subscribe(setHealth);
  }, []);

  useEffect(() => {
    return selfHostedServerMonitor.subscribe(state => setServerStatus(state.status));
  }, []);

  useEffect(() => {
    return tauriBackendService.subscribeToStatus(() => {
      setLocalUrl(tauriBackendService.getBackendUrl());
    });
  }, []);

  const checkHealth = useCallback(async () => {
    return backendHealthMonitor.checkNow();
  }, []);

  const isOnline =
    connectionMode === 'selfhosted'
      ? serverStatus !== 'offline' || !!localUrl
      : health.isOnline;

  return {
    ...health,
    isOnline,
    checkHealth,
  };
}