From d01e576dccbd82c1b7c90ef2abde1c42f03149b7 Mon Sep 17 00:00:00 2001
From: Daniar Mannanov <daniar@dev.tatar>
Date: Tue, 11 Aug 2026 13:23:45 +0300
Subject: [PATCH] Schedule features from mutable regions

---
 internal/world/decoration_region.go      | 22 ++++++++++
 internal/world/decoration_region_test.go | 55 +++++++++++++++++++++---
 2 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/internal/world/decoration_region.go b/internal/world/decoration_region.go
index 02d166d..cbb7e16 100644
--- a/internal/world/decoration_region.go
+++ b/internal/world/decoration_region.go
@@ -128,6 +128,28 @@ func (r *decorationRegion) sourceBiomes() []string {
 	return names
 }
 
+func (r *decorationRegion) scheduledFeatures(stage int) ([]worldgen.ScheduledFeature, error) {
+	set, err := worldgen.LoadFeatureSet()
+	if err != nil {
+		return nil, err
+	}
+	if err := r.ensureSourceNeighborhood(); err != nil {
+		return nil, err
+	}
+	return set.FeatureSchedule(possibleBiomeOrder(), r.sourceBiomes(), stage)
+}
+
+func (r *decorationRegion) ensureSourceNeighborhood() error {
+	for cx := r.sourceX - 1; cx <= r.sourceX+1; cx++ {
+		for cz := r.sourceZ - 1; cz <= r.sourceZ+1; cz++ {
+			if _, ok := r.chunks[[2]int32{cx, cz}]; !ok {
+				return fmt.Errorf("world: source biome neighborhood missing (%d,%d)", cx, cz)
+			}
+		}
+	}
+	return nil
+}
+
 func (r *decorationRegion) placementContext(biomeAllows func(worldgen.FeaturePosition) bool) worldgen.PlacementContext {
 	set, err := worldgen.LoadFeatureSet()
 	if err != nil {
diff --git a/internal/world/decoration_region_test.go b/internal/world/decoration_region_test.go
index 6cff182..b6555ef 100644
--- a/internal/world/decoration_region_test.go
+++ b/internal/world/decoration_region_test.go
@@ -66,10 +66,14 @@ func TestDecorationRegionHeightmapsMatchPlacementSemantics(t *testing.T) {
 }
 
 func TestDecorationRegionSourceBiomesUseThreeByThreeChunks(t *testing.T) {
-	center := NewChunk(0, 0, BiomePlains)
-	east := NewChunk(1, 0, biomeIDByName("minecraft:desert"))
-	outside := NewChunk(2, 0, biomeIDByName("minecraft:forest"))
-	region, err := newDecorationRegion([]*Chunk{center, east, outside})
+	var chunks []*Chunk
+	for cx := int32(-1); cx <= 1; cx++ {
+		for cz := int32(-1); cz <= 1; cz++ {
+			chunks = append(chunks, NewChunk(cx, cz, BiomePlains))
+		}
+	}
+	chunks = append(chunks, NewChunk(2, 0, biomeIDByName("minecraft:forest")))
+	region, err := newDecorationRegion(chunks)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -77,8 +81,49 @@ func TestDecorationRegionSourceBiomesUseThreeByThreeChunks(t *testing.T) {
 		t.Fatal(err)
 	}
 	got := region.sourceBiomes()
-	want := []string{"minecraft:plains", "minecraft:desert"}
+	want := []string{"minecraft:plains"}
 	if !reflect.DeepEqual(got, want) {
 		t.Fatalf("source biomes = %v, want %v", got, want)
 	}
 }
+
+func TestDecorationRegionSchedulesRealFeatureStage(t *testing.T) {
+	var chunks []*Chunk
+	for cx := int32(-1); cx <= 1; cx++ {
+		for cz := int32(-1); cz <= 1; cz++ {
+			chunks = append(chunks, NewChunk(cx, cz, BiomePlains))
+		}
+	}
+	region, err := newDecorationRegion(chunks)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := region.setSource(0, 0); err != nil {
+		t.Fatal(err)
+	}
+	features, err := region.scheduledFeatures(undergroundOresStage)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(features) == 0 {
+		t.Fatal("plains underground stage produced no scheduled features")
+	}
+	for i, feature := range features {
+		if i > 0 && feature.Index <= features[i-1].Index {
+			t.Fatalf("feature %s index %d is not after index %d", feature.Name, feature.Index, features[i-1].Index)
+		}
+	}
+}
+
+func TestDecorationRegionRequiresSourceBiomeNeighborhood(t *testing.T) {
+	region, err := newDecorationRegion([]*Chunk{NewChunk(0, 0, BiomePlains)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := region.setSource(0, 0); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := region.scheduledFeatures(undergroundOresStage); err == nil {
+		t.Fatal("missing source neighborhood succeeded")
+	}
+}