src/game/java/net/minecraft/util/datafix/fixes/ChunkBiomeFix.java

package net.minecraft.util.datafix.fixes;

import com.mojang.datafixers.DSL;
import com.mojang.datafixers.DataFix;
import com.mojang.datafixers.OpticFinder;
import com.mojang.datafixers.TypeRewriteRule;
import com.mojang.datafixers.Typed;
import com.mojang.datafixers.schemas.Schema;
import com.mojang.datafixers.types.Type;
import com.mojang.serialization.Dynamic;
import java.util.Arrays;
import java.util.Optional;
import java.util.stream.IntStream;

public class ChunkBiomeFix extends DataFix {
    public ChunkBiomeFix(Schema p_15014_, boolean p_15015_) {
        super(p_15014_, p_15015_);
    }

    @Override
    protected TypeRewriteRule makeRule() {
        Type<?> type = this.getInputSchema().getType(References.CHUNK);
        OpticFinder<?> opticfinder = type.findField("Level");
        return this.fixTypeEverywhereTyped(
            "Leaves fix", type, p_15018_ -> p_15018_.updateTyped(opticfinder, p_145204_ -> p_145204_.update(DSL.remainderFinder(), p_145206_ -> {
                        Optional<IntStream> optional = p_145206_.get("Biomes").asIntStreamOpt().result();
                        if (optional.isEmpty()) {
                            return p_145206_;
                        } else {
                            int[] aint = optional.get().toArray();
                            if (aint.length != 256) {
                                return p_145206_;
                            } else {
                                int[] aint1 = new int[1024];

                                for (int i = 0; i < 4; i++) {
                                    for (int j = 0; j < 4; j++) {
                                        int k = (j << 2) + 2;
                                        int l = (i << 2) + 2;
                                        int i1 = l << 4 | k;
                                        aint1[i << 2 | j] = aint[i1];
                                    }
                                }

                                for (int j1 = 1; j1 < 64; j1++) {
                                    System.arraycopy(aint1, 0, aint1, j1 * 16, 16);
                                }

                                return p_145206_.set("Biomes", p_145206_.createIntList(Arrays.stream(aint1)));
                            }
                        }
                    }))
        );
    }
}