ui/backend: theme switch using GPIO

pi/backend/gpio_service.py

@@ -0,0 +1,92 @@
+"""GPIO service for Pi Zero - edge-triggered monitoring.
+
+Polls GPIO pins and exposes state changes for inclusion in other payloads.
+Keeps UART separate (handled by arduino_service).
+"""
+
+import gevent
+
+try:
+    import RPi.GPIO as GPIO
+    _GPIO_AVAILABLE = True
+except ImportError:
+    _GPIO_AVAILABLE = False
+    print("[GPIO] RPi.GPIO not available - running in mock mode")
+
+
+# Pin assignments
+PIN_THEME_SWITCH = 20  # Physical switch for light/dark theme
+
+
+class GPIOService:
+    """Monitors GPIO pins and tracks state changes."""
+
+    def __init__(self):
+        self._running = False
+        self._greenlet = None
+
+        # Theme switch state
+        self._theme_switch_state = False  # False = light, True = dark
+        self._theme_switch_pending = None  # None = no change, bool = new value
+
+        if _GPIO_AVAILABLE:
+            GPIO.setmode(GPIO.BCM)
+            GPIO.setwarnings(False)
+            # Input with software pull-down (belt + suspenders with hardware pulldown)
+            GPIO.setup(PIN_THEME_SWITCH, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
+
+    def start(self):
+        """Start background polling."""
+        if self._running:
+            return
+        self._running = True
+
+        # Read initial state
+        if _GPIO_AVAILABLE:
+            self._theme_switch_state = GPIO.input(PIN_THEME_SWITCH) == GPIO.HIGH
+        else:
+            self._theme_switch_state = True  # Mock: default dark
+
+        self._greenlet = gevent.spawn(self._poll_loop)
+        print(f"[GPIO] Started, theme_switch initial={self._theme_switch_state}")
+
+    def stop(self):
+        """Stop background polling."""
+        self._running = False
+        if self._greenlet:
+            self._greenlet.kill()
+            self._greenlet = None
+        if _GPIO_AVAILABLE:
+            GPIO.cleanup([PIN_THEME_SWITCH])
+
+    def _poll_loop(self):
+        """Poll GPIO at ~20Hz, detect edges."""
+        while self._running:
+            gevent.sleep(0.05)  # 20Hz
+
+            if _GPIO_AVAILABLE:
+                current = GPIO.input(PIN_THEME_SWITCH) == GPIO.HIGH
+            else:
+                current = self._theme_switch_state  # Mock: no change
+
+            if current != self._theme_switch_state:
+                self._theme_switch_state = current
+                self._theme_switch_pending = current
+                print(f"[GPIO] Theme switch changed to {current}")
+
+    def get_theme_switch_change(self):
+        """Get pending theme switch change, if any.
+
+        Returns:
+            bool or None: New state if changed since last call, None otherwise.
+        """
+        if self._theme_switch_pending is not None:
+            value = self._theme_switch_pending
+            self._theme_switch_pending = None
+            return value
+        return None
+
+    @property
+    def theme_switch(self):
+        """Current theme switch state (True = dark, False = light)."""
+        return self._theme_switch_state