implement grpc weather

pkg/weather/state/state_get.go

@@ -0,0 +1,87 @@
+package state
+
+import (
+	"context"
+	"errors"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+	"go.opentelemetry.io/otel/trace"
+
+	"gitea.libretechconsulting.com/rmcguire/ambient-local-exporter/pkg/weather"
+)
+
+// Returns last requested number of weather updates
+func (w *WeatherState) Get(ctx context.Context, last int) (
+	[]*weather.WeatherUpdate, error,
+) {
+	if last < 1 {
+		last = 1
+	}
+
+	ctx, span := w.tracer.Start(ctx, "getWeatherState")
+	span.SetAttributes(
+		attribute.Int("last", last),
+		attribute.Int("keep", w.keep),
+		attribute.Int("currentSize", w.Count()),
+	)
+	defer span.End()
+
+	updates, err := w.get(ctx, last)
+	if err != nil {
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+	} else {
+		span.SetStatus(codes.Ok, "")
+	}
+
+	return updates, err
+}
+
+func (w *WeatherState) get(ctx context.Context, last int) (
+	[]*weather.WeatherUpdate, error,
+) {
+	span := trace.SpanFromContext(ctx)
+
+	w.RLock()
+	defer w.Unlock()
+
+	span.AddEvent("acquired lock on state cache")
+
+	updates := w.updates
+
+	if w.count() == 0 {
+		err := errors.New("no state to get")
+		span.RecordError(err)
+		return nil, err
+	} else if w.count() <= last {
+		span.RecordError(errors.New("requested more state than exists"))
+	} else {
+		updates = updates[len(updates)-last:]
+	}
+
+	span.SetAttributes(attribute.Int("retrieved", len(updates)))
+	span.SetStatus(codes.Ok, "")
+
+	return updates, nil
+}
+
+// Returns count of retained weather updates
+func (w *WeatherState) Count() int {
+	_, span := w.tracer.Start(w.ctx, "countWeatherState")
+	defer span.End()
+
+	count := w.count()
+
+	span.SetAttributes(attribute.Int("count", count))
+	span.SetStatus(codes.Ok, "")
+
+	return count
+}
+
+func (w *WeatherState) count() int {
+	w.RLock()
+	defer w.RUnlock()
+
+	return len(w.updates)
+}