Pi vitals module

pi/ui/lib/services/pi_io.dart

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+import 'dart:io';
+
+/// Abstraction for Raspberry Pi hardware I/O
+///
+/// Uses fire-and-forget async reads with synchronous cache returns.
+/// UI always gets immediate response, cache updates in background.
+class PiIO {
+  PiIO._() {
+    // Kick off initial read
+    _refreshTemperature();
+  }
+  static final instance = PiIO._();
+
+  // Thermal zone file path (returns millidegrees)
+  static const _thermalPath = '/sys/class/thermal/thermal_zone0/temp';
+
+  // Cache
+  double? _tempCache;
+  bool _tempReadInProgress = false;
+
+  /// Get CPU temperature in Celsius (synchronous, returns cached value)
+  ///
+  /// Returns immediately with cached value (or null if no read has completed).
+  /// Triggers background refresh if not already in progress.
+  double? getTemperature() {
+    // Fire off background read if not already running
+    if (!_tempReadInProgress) {
+      _refreshTemperature();
+    }
+    return _tempCache;
+  }
+
+  /// Background read - updates cache when complete
+  Future<void> _refreshTemperature() async {
+    if (_tempReadInProgress) return;
+    _tempReadInProgress = true;
+
+    try {
+      final file = File(_thermalPath);
+      if (await file.exists()) {
+        final content = await file.readAsString();
+        _tempCache = int.parse(content.trim()) / 1000.0;
+      }
+    } catch (e) {
+      // Not on Pi, or permission issue - cache stays as-is
+    } finally {
+      _tempReadInProgress = false;
+    }
+  }
+
+  /// Force clear cache (next getTemperature will return null until read completes)
+  void clearCache() {
+    _tempCache = null;
+  }
+}