room camera and rover snapshots

server/src/services/roverSnapshotService/poller.js

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+// Rover Snapshot Poller
+// Purpose: Polls on-disk rover snapshot images and emits frame/status updates as rover files change.
+// Scope: Owns snapshot file IO, stale-rover cleanup, and in-memory state tracking.
+const EventEmitter = require('events');
+const fs = require('fs/promises');
+const path = require('path');
+const logger = require('../../globals/logger').child('roverSnapshot');
+
+const SNAPSHOT_DIR = process.env.ROVER_SNAPSHOT_DIR || '/var/lib/rover-snapshots';
+const POLL_INTERVAL_MS = 300;
+
+const roverState = new Map();
+const events = new EventEmitter();
+let pollTimer = null;
+
+function markState(id, updates = {}) {
+  const prev = roverState.get(id) || {};
+  const next = { ...prev, ...updates };
+  roverState.set(id, next);
+  return next;
+}
+
+function getSnapshotPath(id) {
+  return path.join(SNAPSHOT_DIR, `${id}.jpg`);
+}
+
+function createRoverSnapshotPoller({ roverManager }) {
+  async function fetchSnapshot(id) {
+    const state = roverState.get(id);
+    if (state?.fetching) return;
+    markState(id, { fetching: true });
+    try {
+      const filePath = getSnapshotPath(id);
+      const stats = await fs.stat(filePath);
+      if (state?.mtimeMs && stats.mtimeMs <= state.mtimeMs) return;
+      const buffer = await fs.readFile(filePath);
+      const ts = stats.mtimeMs || Date.now();
+      markState(id, { frame: buffer, ts, error: null, failures: 0, mtimeMs: stats.mtimeMs });
+      events.emit('frame', { id, buffer, ts });
+    } catch (err) {
+      const failures = (state?.failures || 0) + 1;
+      const message = err.code === 'ENOENT' ? 'Snapshot missing' : err.message;
+      markState(id, { error: message, failures });
+      events.emit('status', { id, error: message });
+      if (failures % 20 === 1) logger.warn('Snapshot read failed', { id, err: message });
+    } finally {
+      markState(id, { fetching: false });
+    }
+  }
+
+  function cleanupInactive(activeIds) {
+    roverState.forEach((_, id) => {
+      if (!activeIds.has(id)) roverState.delete(id);
+    });
+  }
+
+  function stopAll() {
+    if (pollTimer) {
+      clearInterval(pollTimer);
+      pollTimer = null;
+    }
+    roverState.clear();
+  }
+
+  function startAll() {
+    stopAll();
+    pollTimer = setInterval(() => {
+      const roster = roverManager.getRoster();
+      const activeIds = new Set(roster.map((entry) => String(entry.id)));
+      cleanupInactive(activeIds);
+      roster.forEach((entry) => fetchSnapshot(String(entry.id)));
+    }, POLL_INTERVAL_MS);
+    logger.info('Started rover snapshot polling');
+  }
+
+  function getRoverSnapshotState(id) {
+    const state = roverState.get(id);
+    if (!state) return null;
+    return {
+      frame: state.frame || null,
+      ts: state.ts || null,
+      error: state.error || null,
+    };
+  }
+
+  return {
+    startAll,
+    stopAll,
+    roverSnapshotEvents: events,
+    getRoverSnapshotState,
+  };
+}
+
+module.exports = {
+  createRoverSnapshotPoller,
+};