initial switch to websocket

pi/backend/throttle.py

@@ -0,0 +1,61 @@
+"""Throttle layer for rate-limiting telemetry emissions."""
+
+import time
+from typing import Any, Callable
+
+
+class Throttle:
+    """Rate limiter for WebSocket emissions.
+
+    Coalesces rapid updates - only emits at most once per min_interval.
+    If multiple updates arrive within the interval, the latest value wins.
+    """
+
+    def __init__(self, min_interval: float = 0.5):
+        """
+        Args:
+            min_interval: Minimum seconds between emissions (default 0.5 = 2Hz max)
+        """
+        self._last_emit: float = 0
+        self._min_interval = min_interval
+        self._pending: Any = None
+
+    def maybe_emit(self, data: Any, emit_fn: Callable[[Any], None]) -> bool:
+        """Emit if interval has passed, otherwise store as pending.
+
+        Args:
+            data: Data to emit
+            emit_fn: Function to call with data when emitting
+
+        Returns:
+            True if emitted, False if stored as pending
+        """
+        now = time.time()
+        if now - self._last_emit >= self._min_interval:
+            emit_fn(data)
+            self._last_emit = now
+            self._pending = None
+            return True
+        else:
+            self._pending = data  # Latest value wins
+            return False
+
+    def flush(self, emit_fn: Callable[[Any], None]) -> bool:
+        """Emit pending data if any.
+
+        Call this periodically to ensure pending data gets sent.
+
+        Returns:
+            True if pending data was emitted, False if nothing pending
+        """
+        if self._pending is not None:
+            emit_fn(self._pending)
+            self._last_emit = time.time()
+            self._pending = None
+            return True
+        return False
+
+    @property
+    def has_pending(self) -> bool:
+        """Check if there's pending data waiting to be emitted."""
+        return self._pending is not None