package gfs

import (
	"math"
	"path/filepath"
	"testing"
	"time"
)

// testVariant is a tiny cube (2 hours × 3 levels × 3 lat × 4 lng) used to
// exercise the sampler without allocating a multi-gigabyte real dataset.
func testVariant() *Variant {
	return &Variant{
		ID:              "gfs-test",
		ResToken:        "test",
		Resolution:      90, // 180/90+1 = 3 lats, 360/90 = 4 lngs
		HourStep:        3,
		MaxHour:         3, // 2 hours
		Pressures:       []int{1000, 500, 100},
		PressuresPgrb2:  []int{1000, 500, 100},
		PressuresPgrb2b: []int{},
	}
}

func TestWindSampler(t *testing.T) {
	v := testVariant()
	path := filepath.Join(t.TempDir(), "cube.bin")
	f, err := Create(path, v)
	if err != nil {
		t.Fatalf("Create: %v", err)
	}

	// HGT increases with level so the altitude bisection has a gradient;
	// U and V are constant so interpolation must return them exactly.
	for h := range v.NumHours() {
		for lvl := range v.NumLevels() {
			for la := range v.NumLatitudes() {
				for ln := range v.NumLongitudes() {
					f.SetVal(h, lvl, VarHeight, la, ln, float32(lvl*1000))
					f.SetVal(h, lvl, VarWindU, la, ln, 7)
					f.SetVal(h, lvl, VarWindV, la, ln, 3)
				}
			}
		}
	}
	f.Flush()
	f.Close()

	epoch := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	rf, err := Open(path, v, epoch)
	if err != nil {
		t.Fatalf("Open: %v", err)
	}
	defer rf.Close()
	w := NewWind(rf)

	// Query at the dataset epoch, equator, lng 45, altitude 500m (between
	// level 0 @ 0m and level 1 @ 1000m).
	s, err := w.Wind(float64(epoch.Unix()), 0, 45, 500)
	if err != nil {
		t.Fatalf("Wind: %v", err)
	}
	if math.Abs(s.U-7) > 1e-5 || math.Abs(s.V-3) > 1e-5 {
		t.Errorf("constant wind not recovered: got U=%v V=%v, want 7,3", s.U, s.V)
	}
	if s.AboveModel {
		t.Errorf("AboveModel should be false at altitude within model range")
	}
}