cleanup to prepare for double camos

src/main/java/fr/adrien1106/reframed/block/ReFramedDoubleEntity.java

@@ -0,0 +1,53 @@
+package fr.adrien1106.reframed.block;
+
+import fr.adrien1106.reframed.ReFramed;
+import net.minecraft.block.BlockState;
+import net.minecraft.block.Blocks;
+import net.minecraft.block.entity.BlockEntityType;
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.nbt.NbtHelper;
+import net.minecraft.registry.Registries;
+import net.minecraft.util.math.BlockPos;
+
+import java.util.Objects;
+
+public class ReFramedDoubleEntity extends ReFramedEntity {
+
+    protected BlockState second_state = Blocks.AIR.getDefaultState();
+
+    public ReFramedDoubleEntity(BlockEntityType<?> type, BlockPos pos, BlockState state) {
+        super(type, pos, state);
+    }
+
+    @Override
+    public BlockState getSecondTheme() {
+        return second_state;
+    }
+
+    public void setSecondTheme(BlockState newState) {
+        if(!Objects.equals(second_state, newState)) {
+            second_state = newState;
+            markDirtyAndDispatch();
+        }
+    }
+
+    @Override
+    public void readNbt(NbtCompound nbt) {
+        super.readNbt(nbt);
+
+        BlockState rendered_state = second_state;// keep previous state to check if rerender is needed
+        first_state = NbtHelper.toBlockState(Registries.BLOCK.getReadOnlyWrapper(), nbt.getCompound(BLOCKSTATE_KEY + 2));
+
+        // Force a chunk remesh on the client if the displayed blockstate has changed
+        if(world != null && world.isClient && !Objects.equals(rendered_state, second_state)) {
+            ReFramed.chunkRerenderProxy.accept(world, pos);
+        }
+    }
+
+    @Override
+    public void writeNbt(NbtCompound nbt) {
+        super.writeNbt(nbt);
+
+        if(second_state != Blocks.AIR.getDefaultState()) nbt.put(BLOCKSTATE_KEY + 2, NbtHelper.fromBlockState(second_state));
+    }
+}