add sandbox observability contracts

adapter/observability/noop.py

@@ -20,6 +20,14 @@ class NoopMetrics:
     ) -> None:
         return None
 
+    def set(
+        self,
+        name: str,
+        value: int | float,
+        attrs: Attrs | None = None,
+    ) -> None:
+        return None
+
 
 class NoopSpan:
     def set_attribute(self, name: str, value: AttrValue) -> None:

adapter/otel/metrics.py

@@ -5,12 +5,21 @@ from opentelemetry.metrics import Counter, Histogram, Meter
 from usecase.interface import Attrs
 
 
+class _GaugeAdapter:
+    def __init__(self, gauge: object) -> None:
+        self._gauge = gauge
+
+    def set(self, value: int | float, attributes: object = None) -> None:
+        getattr(self._gauge, 'set')(value, attributes=attributes)
+
+
 class OtelMetrics:
     def __init__(self, meter: Meter) -> None:
         self._meter = meter
         self._lock = Lock()
         self._counters: dict[str, Counter] = {}
         self._histograms: dict[str, Histogram] = {}
+        self._gauges: dict[str, _GaugeAdapter] = {}
 
     def increment(
         self,
@@ -34,6 +43,17 @@ class OtelMetrics:
             attributes=None if attrs is None else dict(attrs),
         )
 
+    def set(
+        self,
+        name: str,
+        value: int | float,
+        attrs: Attrs | None = None,
+    ) -> None:
+        self._gauge(name).set(
+            value,
+            attributes=None if attrs is None else dict(attrs),
+        )
+
     def _counter(self, name: str) -> Counter:
         counter = self._counters.get(name)
         if counter is not None:
@@ -57,3 +77,15 @@ class OtelMetrics:
                 histogram = self._meter.create_histogram(name)
                 self._histograms[name] = histogram
         return histogram
+
+    def _gauge(self, name: str) -> _GaugeAdapter:
+        gauge = self._gauges.get(name)
+        if gauge is not None:
+            return gauge
+
+        with self._lock:
+            gauge = self._gauges.get(name)
+            if gauge is None:
+                gauge = _GaugeAdapter(self._meter.create_gauge(name))
+                self._gauges[name] = gauge
+        return gauge