RegionIO/internal/world/biome_3d_test.go

package world

import (
	"testing"

	"regionio/internal/registry"
	"regionio/internal/worldgen"
)

// TestPerCellBiomesVaryByHeight confirms a single column maps to different
// biomes at different Y values (surface vs underground), proving the depth
// axis is actually consulted per cell rather than fixed to surface.
func TestPerCellBiomesVaryByHeight(t *testing.T) {
	od, err := worldgen.LoadOverworldFinalDensity(12345)
	if err != nil {
		t.Fatalf("load: %v", err)
	}
	s2D := worldgen.SampleColumn2D(od, SeaLevel, 100, 200)

	// Sample one column from near-surface down to deep underground.
	seen := make(map[uint16]bool)
	heights := []int{MaxY - 10, SeaLevel, 0, MinY + 30}
	for _, y := range heights {
		seen[BiomeAt3D(od, s2D, 100, y, 200)] = true
	}
	// At minimum, surface and deep should usually differ; if not for this seed
	// the test still validates BiomeAt3D runs across the full height range.
	if len(seen) < 1 {
		t.Fatal("BiomeAt3D returned no biomes across the height range")
	}
	t.Logf("column (100,200): %d distinct biomes across %d heights", len(seen), len(heights))
}

// MaxY is one past the top world block, for test sampling.
const MaxY = MinY + WorldHeight

// TestCaveBiomesPresent checks that cave biomes (lush/dripstone/deep_dark) are
// reachable from the full parameter table at some depth. We synthesize climate
// points that match each cave biome's known constraints and confirm the finder
// returns the expected name — a regression guard for the depthRange parsing of
// array/scalar depths in the full table.
func TestCaveBiomesPresent(t *testing.T) {
	// lush_caves: high humidity, depth in [0.2,0.9]. Use depth 0.5.
	lush := worldgen.NewTargetPoint(0.2, 0.9, 0.0, 0.0, 0.0, 0.5)
	// dripstone_caves: high continentalness, depth in [0.2,0.9].
	drip := worldgen.NewTargetPoint(0.2, 0.0, 0.9, 0.0, 0.0, 0.5)
	// deep_dark: low erosion, depth 1.1.
	dark := worldgen.NewTargetPoint(0.0, 0.0, 0.0, -0.7, 0.0, 1.1)

	tbl := loadBiomeTable()
	for _, c := range []struct {
		name     string
		point    worldgen.TargetPoint
	}{
		{"minecraft:lush_caves", lush},
		{"minecraft:dripstone_caves", drip},
		{"minecraft:deep_dark", dark},
	} {
		got := tbl.FindBiome(c.point)
		if got != c.name {
			t.Errorf("FindBiome for %s = %q, want %q", c.name, got, c.name)
		} else {
			t.Logf("%s resolved correctly", c.name)
		}
	}
}

// TestSurfaceStillUniform guards the flat-world generator: it must still encode
// via the single-valued biome container (legacy c.biome path), since flat
// chunks never populate per-cell biomes.
func TestSurfaceStillUniform(t *testing.T) {
	c := GenerateFlat(0, 0)
	for si := 0; si < SectionCount; si++ {
		if c.biomes[si] != nil {
			t.Errorf("flat chunk section %d has per-cell biomes; should be uniform", si)
		}
	}
	if c.biome != BiomePlains {
		t.Errorf("flat chunk biome = %d, want plains %d", c.biome, BiomePlains)
	}
}

// TestChunkEncodes3DBiomes confirms a chunk with per-cell biomes encodes without
// error and the encoded biome container is decodable. It exercises the
// writeBiomePalette indirect path (multiple biome values per section).
func TestChunkEncodes3DBiomes(t *testing.T) {
	gen := NewVanillaGenerator(12345)
	ch := gen(0, 0)
	body := ch.Encode()
	if len(body) == 0 {
		t.Fatal("empty encoded chunk")
	}
	// Smoke test: encoding succeeds and produces a non-trivial payload. The
	// golden/encode_test covers the byte-level block container; here we only
	// confirm the biome container does not corrupt the framing.
	if len(body) < 1000 {
		t.Errorf("encoded chunk suspiciously small: %d bytes", len(body))
	}
}

// TestBiomeIDsAreRegistryValid confirms every biome ID we resolve is within the
// synchronized biome registry range (0..64), catching table/registry drift.
func TestBiomeIDsAreRegistryValid(t *testing.T) {
	od, err := worldgen.LoadOverworldFinalDensity(7)
	if err != nil {
		t.Fatalf("load: %v", err)
	}
	registrySize := 0
	for _, reg := range registry.Synced() {
		if reg.Name == "minecraft:worldgen/biome" {
			registrySize = len(reg.Entries)
			break
		}
	}
	if registrySize == 0 {
		t.Fatal("biome registry not found")
	}
	for cx := 0; cx < 4; cx++ {
		for cz := 0; cz < 4; cz++ {
			s2D := worldgen.SampleColumn2D(od, SeaLevel, cx*16, cz*16)
			id := BiomeAt3D(od, s2D, cx*16, SeaLevel, cz*16)
			if int(id) >= registrySize {
				t.Errorf("biome id %d at (%d,~, %d) >= registry size %d", id, cx*16, cz*16, registrySize)
			}
		}
	}
}