signalk-data-age-watchdog/index.js

Signal K plugin to monitor the freshness (age) of timestamped data from any specified data paths. Triggers visual/sound notifications if data becomes stale.

module.exports = (app) => {
  let intervalId;

  const plugin = {
    id: 'signalk-data-age-watchdog',
    name: 'Data Age Watchdog',
    description: 'Computes the age of data from multiple paths and triggers alerts if data is old.',

    start: (settings) => {
      app.debug('data age watchdog plugin started');

      intervalId = setInterval(() => {
        if (!Array.isArray(settings.paths)) return;

        settings.paths.forEach(path => {
          const outputPath = path + '.dataAge';
          const value = app.getSelfPath(path);
          const timestamp = value?.timestamp;

          if (!timestamp) return;

          const ageSeconds = (Date.now() - new Date(timestamp).getTime()) / 1000;

          app.handleMessage('plugin-data-age-watchdog', {
            context: 'vessels.self',
            updates: [{
              source: { label: 'data-age-watchdog' },
              timestamp: new Date().toISOString(),
              values: [{
                path: outputPath,
                value: ageSeconds
              }]
            }]
          });

          if (ageSeconds > (settings?.maxAgeSeconds || 60)) {
            app.handleMessage('notifications', {
              updates: [{
                values: [{
                  path: `notifications.${outputPath}.dataStale`,
                  value: {
                    state: 'alarm',
                    method: ['visual', 'sound'],
                    message: `Data is stale on ${path}: ${Math.round(ageSeconds)} seconds old`
                  }
                }]
              }]
            });
          }
        });
      }, 1000);
    },

    stop: () => {
      app.debug('data-age watchdog plugin stopped');
      if (intervalId) clearInterval(intervalId);
    },

    schema: () => ({
      type: 'object',
      properties: {
        paths: {
          type: 'array',
          title: 'Paths to monitor',
          items: {
            type: 'string'
          },
          minItems: 1,
          default: ['navigation.position']
        },
        maxAgeSeconds: {
          type: 'integer',
          title: 'Maximum allowed data age (seconds)',
          default: 60,
          minimum: 1
        }
      }
    })
  };

  return plugin;
};