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)
}