fix: anchor growth forecasts to real Tehran date

internal/insight/time.go

@@ -0,0 +1,49 @@
+package insight
+
+import "time"
+
+type Freshness string
+
+const (
+	FreshnessFresh   Freshness = "FRESH"
+	FreshnessLagging Freshness = "LAGGING"
+	FreshnessStale   Freshness = "STALE"
+)
+
+type TimeContext struct {
+	AsOfDate          string    `json:"asOfDate"`
+	DataThroughDate   string    `json:"dataThroughDate"`
+	ForecastStartDate string    `json:"forecastStartDate"`
+	Freshness         Freshness `json:"freshness"`
+	DataLagDays       int       `json:"dataLagDays"`
+}
+
+func BuildTimeContext(now, dataThrough time.Time) TimeContext {
+	location, err := time.LoadLocation("Asia/Tehran")
+	if err != nil {
+		location = time.FixedZone("Asia/Tehran", 3*60*60+30*60)
+	}
+	today := dateOnly(now.In(location), location)
+	through := dateOnly(dataThrough.In(location), location)
+	lag := max(0, int(today.Sub(through).Hours()/24))
+	return TimeContext{
+		AsOfDate: today.Format(time.DateOnly), DataThroughDate: through.Format(time.DateOnly),
+		ForecastStartDate: today.Format(time.DateOnly), Freshness: ClassifyFreshness(lag), DataLagDays: lag,
+	}
+}
+
+func ClassifyFreshness(lagDays int) Freshness {
+	switch {
+	case lagDays <= 1:
+		return FreshnessFresh
+	case lagDays <= 7:
+		return FreshnessLagging
+	default:
+		return FreshnessStale
+	}
+}
+
+func dateOnly(value time.Time, location *time.Location) time.Time {
+	year, month, day := value.In(location).Date()
+	return time.Date(year, month, day, 0, 0, 0, 0, location)
+}