engine refactor

internal/weather/gfs/gefs_variants.go

@@ -0,0 +1,68 @@
+package gfs
+
+import "fmt"
+
+// Family is the dataset family ("gfs" or "gefs"). Variants of different
+// families have different URL layouts but share the cube format.
+type Family int
+
+const (
+	FamilyGFS Family = iota
+	FamilyGEFS
+)
+
+func (f Family) String() string {
+	switch f {
+	case FamilyGEFS:
+		return "gefs"
+	default:
+		return "gfs"
+	}
+}
+
+// HasMember reports whether the family requires a member index in URLs.
+func (f Family) HasMember() bool { return f == FamilyGEFS }
+
+// GEFS variant constants.
+//
+// The 21-member ensemble is gec00 (control) + gep01..gep20 (perturbations).
+// NOAA publishes more members today but 21 matches the historical Tawhiri
+// configuration and is what the phase 2 spec calls for.
+const GEFSMembers = 21
+
+// GefsMemberName returns the file-name token for a GEFS member.
+// member=0 → "gec00", member=1..20 → "gep01".."gep20".
+func GefsMemberName(member int) string {
+	if member == 0 {
+		return "gec00"
+	}
+	return fmt.Sprintf("gep%02d", member)
+}
+
+// GEFS S3 mirror.
+const GEFSS3BaseURL = "https://noaa-gefs-pds.s3.amazonaws.com"
+
+// GefsGribURL returns the S3 URL for a GEFS primary GRIB file.
+func GefsGribURL(date string, runHour, member, forecastStep int, resToken string) string {
+	return fmt.Sprintf("%s/gefs.%s/%02d/atmos/pgrb2ap5/%s.t%02dz.pgrb2a.%s.f%03d",
+		GEFSS3BaseURL, date, runHour, GefsMemberName(member), runHour, resToken, forecastStep)
+}
+
+// GefsGribURLB returns the S3 URL for a GEFS secondary GRIB file.
+func GefsGribURLB(date string, runHour, member, forecastStep int, resToken string) string {
+	return fmt.Sprintf("%s/gefs.%s/%02d/atmos/pgrb2bp5/%s.t%02dz.pgrb2b.%s.f%03d",
+		GEFSS3BaseURL, date, runHour, GefsMemberName(member), runHour, resToken, forecastStep)
+}
+
+// GEFS variants — 0.5° resolution, 3-hour cadence, 192h horizon.
+var GEFS0p50_3h = &Variant{
+	ID:              "gefs-0p50-3h",
+	Family:          FamilyGEFS,
+	ResToken:        "0p50",
+	Resolution:      0.5,
+	HourStep:        3,
+	MaxHour:         192,
+	Pressures:       GFS0p50_3h.Pressures,
+	PressuresPgrb2:  GFS0p50_3h.PressuresPgrb2,
+	PressuresPgrb2b: GFS0p50_3h.PressuresPgrb2b,
+}