Add daily coverage planning helper

internal/app/batch_plan.go

@@ -0,0 +1,66 @@
+package app
+
+import (
+	"time"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+func eligibleDailyDates(hourly *weatherdata.ForecastRun, now time.Time, location *time.Location) []time.Time {
+	if hourly == nil || location == nil || hourly.Product != "hourly" || len(hourly.Periods) == 0 {
+		return nil
+	}
+
+	hourlyStarts := make(map[time.Time]struct{}, len(hourly.Periods))
+	var maxLocalDate time.Time
+	for _, period := range hourly.Periods {
+		if !isHourlyPeriod(period) {
+			continue
+		}
+		start := period.StartTime
+		hourlyStarts[instantKey(start)] = struct{}{}
+		localDate := localDateStart(start, location)
+		if maxLocalDate.IsZero() || localDate.After(maxLocalDate) {
+			maxLocalDate = localDate
+		}
+	}
+	if len(hourlyStarts) == 0 || maxLocalDate.IsZero() {
+		return nil
+	}
+
+	startDate := localDateStart(now.In(location).AddDate(0, 0, 2), location)
+	var dates []time.Time
+	for candidate := startDate; !candidate.After(maxLocalDate); candidate = candidate.AddDate(0, 0, 1) {
+		if hasFullHourlyCoverage(candidate, location, hourlyStarts) {
+			dates = append(dates, candidate)
+		}
+	}
+	return dates
+}
+
+func isHourlyPeriod(period weatherdata.ForecastPeriod) bool {
+	if period.StartTime.IsZero() || period.EndTime.IsZero() {
+		return false
+	}
+	return period.EndTime.Equal(period.StartTime.Add(time.Hour))
+}
+
+func hasFullHourlyCoverage(date time.Time, location *time.Location, hourlyStarts map[time.Time]struct{}) bool {
+	day := timeutil.CivilDay(date, location)
+	for required := day.Start; required.Before(day.End); required = required.Add(time.Hour) {
+		if _, ok := hourlyStarts[instantKey(required)]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+func instantKey(value time.Time) time.Time {
+	return value.UTC()
+}
+
+func localDateStart(value time.Time, location *time.Location) time.Time {
+	local := value.In(location)
+	return time.Date(local.Year(), local.Month(), local.Day(), 0, 0, 0, 0, location)
+}