Add timezone support to /forecast/hourly endpoint

internal/adapters/inbound/httpapi/presenter/payload_test.go

@@ -64,7 +64,7 @@ func TestForecastPayloadUS(t *testing.T) {
 		}},
 	}
 
-	payload := ForecastPayload(run, UnitsUS, 2)
+	payload := ForecastPayload(run, UnitsUS, 2, nil)
 	converted, ok := payload.(WeatherForecastRunUS)
 	if !ok {
 		t.Fatalf("expected WeatherForecastRunUS payload, got %T", payload)
@@ -83,6 +83,81 @@ func TestForecastPayloadUS(t *testing.T) {
 	assertApprox(t, period.SnowfallDepthIn, 2.0, 0.0001)
 }
 
+func TestForecastPayloadTimezoneConversionMetricAndUS(t *testing.T) {
+	loc := time.FixedZone("UTC-05:00", -5*60*60)
+	issuedAt := time.Date(2026, 7, 10, 12, 0, 0, 0, time.UTC)
+	updatedAt := issuedAt.Add(30 * time.Minute)
+	run := &model.WeatherForecastRun{
+		Product:   model.ForecastProductHourly,
+		IssuedAt:  issuedAt,
+		UpdatedAt: &updatedAt,
+		Periods: []model.WeatherForecastPeriod{{
+			StartTime:     issuedAt.Add(1 * time.Hour),
+			EndTime:       issuedAt.Add(2 * time.Hour),
+			ConditionCode: model.WMOUnknown,
+		}},
+	}
+
+	metricPayload := ForecastPayload(run, UnitsMetric, 0, loc)
+	metric, ok := metricPayload.(*model.WeatherForecastRun)
+	if !ok {
+		t.Fatalf("expected metric payload type *model.WeatherForecastRun, got %T", metricPayload)
+	}
+	assertOffsetSeconds(t, metric.IssuedAt, -5*60*60)
+	assertOffsetSeconds(t, *metric.UpdatedAt, -5*60*60)
+	assertOffsetSeconds(t, metric.Periods[0].StartTime, -5*60*60)
+	assertOffsetSeconds(t, metric.Periods[0].EndTime, -5*60*60)
+	if !metric.IssuedAt.UTC().Equal(issuedAt) {
+		t.Fatalf("expected metric issuedAt to preserve instant")
+	}
+
+	usPayload := ForecastPayload(run, UnitsUS, 0, loc)
+	us, ok := usPayload.(WeatherForecastRunUS)
+	if !ok {
+		t.Fatalf("expected us payload type WeatherForecastRunUS, got %T", usPayload)
+	}
+	assertOffsetSeconds(t, us.IssuedAt, -5*60*60)
+	assertOffsetSeconds(t, *us.UpdatedAt, -5*60*60)
+	assertOffsetSeconds(t, us.Periods[0].StartTime, -5*60*60)
+	assertOffsetSeconds(t, us.Periods[0].EndTime, -5*60*60)
+
+	// Source model remains untouched.
+	assertOffsetSeconds(t, run.IssuedAt, 0)
+	assertOffsetSeconds(t, *run.UpdatedAt, 0)
+}
+
+func TestForecastPayloadNoTimezonePreservesUTCAndCopySemantics(t *testing.T) {
+	issuedAt := time.Date(2026, 7, 10, 12, 0, 0, 0, time.UTC)
+	updatedAt := issuedAt.Add(time.Hour)
+	run := &model.WeatherForecastRun{
+		Product:   model.ForecastProductHourly,
+		IssuedAt:  issuedAt,
+		UpdatedAt: &updatedAt,
+		Periods: []model.WeatherForecastPeriod{{
+			StartTime:     issuedAt,
+			EndTime:       issuedAt.Add(time.Hour),
+			ConditionCode: model.WMOUnknown,
+		}},
+	}
+
+	metricPayload := ForecastPayload(run, UnitsMetric, 0, nil)
+	metric, ok := metricPayload.(*model.WeatherForecastRun)
+	if !ok {
+		t.Fatalf("expected metric payload type *model.WeatherForecastRun, got %T", metricPayload)
+	}
+	if metric == run {
+		t.Fatalf("expected metric payload to be copied")
+	}
+	if metric.UpdatedAt == run.UpdatedAt {
+		t.Fatalf("expected updatedAt pointer to be copied")
+	}
+	if !metric.IssuedAt.Equal(run.IssuedAt) {
+		t.Fatalf("expected issuedAt to remain unchanged without timezone flag")
+	}
+	assertOffsetSeconds(t, metric.IssuedAt, 0)
+	assertOffsetSeconds(t, metric.Periods[0].StartTime, 0)
+}
+
 func TestMetricCopyAndNilHandling(t *testing.T) {
 	obs := &model.WeatherObservation{
 		TemperatureC: float64Ptr(20.6),
@@ -104,7 +179,7 @@ func TestMetricCopyAndNilHandling(t *testing.T) {
 	if ObservationPayload(nil, UnitsUS, 0) != nil {
 		t.Fatalf("expected nil observation input to return nil payload")
 	}
-	if ForecastPayload(nil, UnitsUS, 0) != nil {
+	if ForecastPayload(nil, UnitsUS, 0, nil) != nil {
 		t.Fatalf("expected nil forecast input to return nil payload")
 	}
 	if AlertsPayload(nil, UnitsUS) != nil {
@@ -190,7 +265,7 @@ func TestForecastPayloadLatitudeLongitudeNotRounded(t *testing.T) {
 		IssuedAt:        time.Now().UTC(),
 	}
 
-	metricPayload := ForecastPayload(run, UnitsMetric, 0)
+	metricPayload := ForecastPayload(run, UnitsMetric, 0, nil)
 	metric, ok := metricPayload.(*model.WeatherForecastRun)
 	if !ok {
 		t.Fatalf("expected metric payload type *model.WeatherForecastRun, got %T", metricPayload)
@@ -199,7 +274,7 @@ func TestForecastPayloadLatitudeLongitudeNotRounded(t *testing.T) {
 	assertApprox(t, metric.Longitude, -90.199456, 0.000001)
 	assertApprox(t, metric.ElevationMeters, 10, 0.0001)
 
-	usPayload := ForecastPayload(run, UnitsUS, 0)
+	usPayload := ForecastPayload(run, UnitsUS, 0, nil)
 	us, ok := usPayload.(WeatherForecastRunUS)
 	if !ok {
 		t.Fatalf("expected us payload type WeatherForecastRunUS, got %T", usPayload)
@@ -225,3 +300,11 @@ func assertApprox(t *testing.T, got *float64, want, eps float64) {
 		t.Fatalf("expected %f +/- %f, got %f", want, eps, *got)
 	}
 }
+
+func assertOffsetSeconds(t *testing.T, ts time.Time, want int) {
+	t.Helper()
+	_, got := ts.Zone()
+	if got != want {
+		t.Fatalf("expected offset %d, got %d for %s", want, got, ts.Format(time.RFC3339))
+	}
+}