Add forecast daypart derivation

internal/forecast/dayparts.go

@@ -0,0 +1,53 @@
+package forecast
+
+import (
+	"fmt"
+	"time"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
+)
+
+type DaypartDefinition struct {
+	Name  string `json:"name"`
+	Start string `json:"start"`
+	End   string `json:"end"`
+}
+
+type DaypartWindow struct {
+	Name   string          `json:"name"`
+	Start  time.Time       `json:"start"`
+	End    time.Time       `json:"end"`
+	Period timeutil.Period `json:"period"`
+}
+
+func ResolveDayparts(date time.Time, location *time.Location, definitions []DaypartDefinition) ([]DaypartWindow, error) {
+	if len(definitions) == 0 {
+		return nil, fmt.Errorf("daypart definitions are required")
+	}
+	windows := make([]DaypartWindow, 0, len(definitions))
+	for i, def := range definitions {
+		if def.Name == "" {
+			return nil, fmt.Errorf("daypart[%d].name is required", i)
+		}
+		startClock, err := timeutil.ParseClock(def.Start)
+		if err != nil {
+			return nil, fmt.Errorf("daypart[%d].start: %w", i, err)
+		}
+		endClock, err := timeutil.ParseClock(def.End)
+		if err != nil {
+			return nil, fmt.Errorf("daypart[%d].end: %w", i, err)
+		}
+		period := timeutil.ClockWindow(date, location, startClock, endClock)
+		windows = append(windows, DaypartWindow{
+			Name:   def.Name,
+			Start:  period.Start,
+			End:    period.End,
+			Period: period,
+		})
+	}
+	return windows, nil
+}
+
+func PeriodForForecastPeriod(period ForecastPeriod) timeutil.Period {
+	return timeutil.Period{Start: period.StartTime, End: period.EndTime}
+}