package grib

import (
	"fmt"
	"hash/fnv"
	"time"
)

// Generate steps from 0 to 96 with step 1 hour (97 steps total)
// GFS provides hourly data for 0-120 hours, we use first 96 hours
var steps = func() []int {
	result := make([]int, 0, 97)
	for i := 0; i <= 96; i++ {
		result = append(result, i)
	}
	return result
}()

func nearestRun(t time.Time) time.Time {
	h := t.UTC().Hour() - t.UTC().Hour()%6
	return time.Date(t.Year(), t.Month(), t.Day(), h, 0, 0, 0, time.UTC)
}

func fileName(run time.Time, step int) string {
	return fmt.Sprintf("gfs.t%02dz.pgrb2.0p50.f%03d", run.Hour(), step)
}

func encodeKey(a ...any) uint64 {
	h := fnv.New64a()
	for _, v := range a {
		fmt.Fprint(h, v)
	}
	return h.Sum64()
}