Add 3-Day Outlook generation

internal/forecast/derive.go

@@ -100,6 +100,62 @@ func BuildDailySummary(bundle *Bundle, date time.Time, location *time.Location,
 	return summary, nil
 }
 
+func BuildPeriodDailySummaries(bundle *Bundle, period timeutil.Period, location *time.Location, dayparts []DaypartDefinition) ([]DailySummary, error) {
+	if !period.IsValid() {
+		return nil, fmt.Errorf("valid forecast period is required")
+	}
+	if location == nil {
+		location = time.UTC
+	}
+	var summaries []DailySummary
+	for day := timeutil.CivilDay(period.Start, location); day.Start.Before(period.End); day = timeutil.CivilDay(day.Start.AddDate(0, 0, 1), location) {
+		overlap, ok := day.Intersection(period)
+		if !ok {
+			continue
+		}
+		summary, err := buildDailySummaryForPeriod(bundle, overlap, location, dayparts)
+		if err != nil {
+			return nil, err
+		}
+		summaries = append(summaries, *summary)
+	}
+	return summaries, nil
+}
+
+func buildDailySummaryForPeriod(bundle *Bundle, period timeutil.Period, location *time.Location, dayparts []DaypartDefinition) (*DailySummary, error) {
+	if bundle == nil {
+		return nil, fmt.Errorf("forecast bundle is required")
+	}
+	if bundle.Hourly == nil || len(bundle.Hourly.Periods) == 0 {
+		return nil, fmt.Errorf("hourly forecast data is required")
+	}
+	windows, err := ResolveDayparts(period.Start, location, dayparts)
+	if err != nil {
+		return nil, err
+	}
+	alerts := AlertOverlaps(bundle.Alerts, period)
+	summary := &DailySummary{
+		Date:             period.Start.In(location).Format(timeutil.DateLayout),
+		Period:           period,
+		NarrativePeriods: SelectNarrativePeriods(bundle, period),
+		AlertOverlaps:    alerts,
+		Discussion:       SelectDiscussion(bundle),
+		SourceWarnings:   bundle.Warnings,
+		SourceProvenance: bundle.Sources,
+	}
+	for _, window := range windows {
+		clipped, ok := window.Period.Intersection(period)
+		if !ok {
+			continue
+		}
+		periods := SelectHourlyPeriods(bundle.Hourly, clipped)
+		daypartSummary := SummarizeDaypart(window.Name, clipped, periods)
+		daypartSummary.AlertOverlaps = overlapsWithin(alerts, clipped)
+		summary.Dayparts = append(summary.Dayparts, daypartSummary)
+	}
+	return summary, nil
+}
+
 func SelectHourlyPeriods(run *ForecastRun, period timeutil.Period) []ForecastPeriod {
 	if run == nil {
 		return nil