Update wind direction and precipitation window presentation

internal/forecast/derive.go

@@ -47,6 +47,8 @@ type TimedValue struct {
 	Time  time.Time `json:"time"`
 }
 
+const DefaultPrecipWindowProbabilityThreshold = 40
+
 type Indicators struct {
 	Snow bool `json:"snow,omitempty"`
 	Ice  bool `json:"ice,omitempty"`
@@ -66,34 +68,101 @@ type AlertOverlap struct {
 }
 
 type PrecipTiming struct {
-	MaxPrecipitationProbability *TimedValue `json:"maxPrecipitationProbability,omitempty"`
-	FirstPrecipitation          *TimedValue `json:"firstPrecipitation,omitempty"`
-	LastPrecipitation           *TimedValue `json:"lastPrecipitation,omitempty"`
-	ThunderMentioned            bool        `json:"thunderMentioned,omitempty"`
+	MaxPrecipitationProbability *TimedValue           `json:"maxPrecipitationProbability,omitempty"`
+	FirstPrecipitation          *TimedValue           `json:"firstPrecipitation,omitempty"`
+	LastPrecipitation           *TimedValue           `json:"lastPrecipitation,omitempty"`
+	ProbabilityThreshold        float64               `json:"probabilityThreshold"`
+	PrecipitationWindows        []PrecipitationWindow `json:"precipitationWindows,omitempty"`
+	ThunderMentioned            bool                  `json:"thunderMentioned,omitempty"`
+}
+
+type PrecipitationWindow struct {
+	Start                       time.Time  `json:"start"`
+	End                         *time.Time `json:"end,omitempty"`
+	MaxPrecipitationProbability TimedValue `json:"maxPrecipitationProbability"`
+	ProbabilityThreshold        float64    `json:"probabilityThreshold"`
 }
 
 func BuildPrecipTiming(periods []weatherdata.ForecastPeriod) PrecipTiming {
-	var timing PrecipTiming
-	for _, forecastPeriod := range periods {
-		setMaxTimedValue(&timing.MaxPrecipitationProbability, forecastPeriod.ProbabilityOfPrecipitationPercent, forecastPeriod.StartTime)
-		if forecastPeriod.ProbabilityOfPrecipitationPercent != nil && *forecastPeriod.ProbabilityOfPrecipitationPercent > 0 {
-			value := TimedValue{
-				Value: *forecastPeriod.ProbabilityOfPrecipitationPercent,
+	return buildPrecipTimingWithThreshold(periods, DefaultPrecipWindowProbabilityThreshold)
+}
+
+func buildPrecipTimingWithThreshold(periods []weatherdata.ForecastPeriod, threshold float64) PrecipTiming {
+	timing := PrecipTiming{ProbabilityThreshold: threshold}
+	sorted := append([]weatherdata.ForecastPeriod(nil), periods...)
+	sort.SliceStable(sorted, func(i int, j int) bool {
+		return sorted[i].StartTime.Before(sorted[j].StartTime)
+	})
+
+	var active *PrecipitationWindow
+	var activeLastEnd time.Time
+	closeActive := func() {
+		if active == nil {
+			return
+		}
+		end := activeLastEnd
+		active.End = &end
+		timing.PrecipitationWindows = append(timing.PrecipitationWindows, *active)
+		active = nil
+	}
+	startActive := func(forecastPeriod weatherdata.ForecastPeriod, probability float64) {
+		active = &PrecipitationWindow{
+			Start: forecastPeriod.StartTime,
+			MaxPrecipitationProbability: TimedValue{
+				Value: probability,
+				Time:  forecastPeriod.StartTime,
+			},
+			ProbabilityThreshold: threshold,
+		}
+		activeLastEnd = forecastPeriod.EndTime
+		if timing.FirstPrecipitation == nil {
+			timing.FirstPrecipitation = &TimedValue{
+				Value: probability,
 				Time:  forecastPeriod.StartTime,
 			}
-			if timing.FirstPrecipitation == nil || value.Time.Before(timing.FirstPrecipitation.Time) {
-				copied := value
-				timing.FirstPrecipitation = &copied
-			}
-			if timing.LastPrecipitation == nil || value.Time.After(timing.LastPrecipitation.Time) {
-				copied := value
-				timing.LastPrecipitation = &copied
+		}
+	}
+
+	for _, forecastPeriod := range sorted {
+		setMaxTimedValue(&timing.MaxPrecipitationProbability, forecastPeriod.ProbabilityOfPrecipitationPercent, forecastPeriod.StartTime)
+		if forecastPeriod.ProbabilityOfPrecipitationPercent == nil || *forecastPeriod.ProbabilityOfPrecipitationPercent < threshold {
+			closeActive()
+		} else {
+			probability := *forecastPeriod.ProbabilityOfPrecipitationPercent
+			if active == nil {
+				startActive(forecastPeriod, probability)
+			} else {
+				if forecastPeriod.StartTime.After(activeLastEnd) {
+					closeActive()
+					startActive(forecastPeriod, probability)
+				}
+				if probability > active.MaxPrecipitationProbability.Value {
+					active.MaxPrecipitationProbability = TimedValue{
+						Value: probability,
+						Time:  forecastPeriod.StartTime,
+					}
+				}
+				if forecastPeriod.EndTime.After(activeLastEnd) {
+					activeLastEnd = forecastPeriod.EndTime
+				}
 			}
 		}
 		if mentionsThunder(forecastPeriod.TextDescription) {
 			timing.ThunderMentioned = true
 		}
 	}
+	if active != nil {
+		timing.PrecipitationWindows = append(timing.PrecipitationWindows, *active)
+	}
+	if len(timing.PrecipitationWindows) > 0 {
+		final := timing.PrecipitationWindows[len(timing.PrecipitationWindows)-1]
+		if final.End != nil {
+			timing.LastPrecipitation = &TimedValue{
+				Value: final.MaxPrecipitationProbability.Value,
+				Time:  *final.End,
+			}
+		}
+	}
 	return timing
 }