Synchronize initial data to the client when an entity starts being tracked

src/main/java/com/minelittlepony/unicopia/mixin/server/MixinEntityTrackerEntry.java

@@ -0,0 +1,29 @@
+package com.minelittlepony.unicopia.mixin.server;
+
+import java.util.function.Consumer;
+
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import com.minelittlepony.unicopia.network.track.Trackable;
+
+import net.minecraft.entity.Entity;
+import net.minecraft.network.listener.ClientPlayPacketListener;
+import net.minecraft.network.packet.Packet;
+import net.minecraft.server.network.EntityTrackerEntry;
+import net.minecraft.server.network.ServerPlayerEntity;
+
+@Mixin(EntityTrackerEntry.class)
+abstract class MixinEntityTrackerEntry {
+    @Shadow
+    private @Final Entity entity;
+
+    @Inject(method = "sendPackets", at = @At("RETURN"))
+    private void onSendPackets(ServerPlayerEntity player, Consumer<Packet<ClientPlayPacketListener>> sender, CallbackInfo info) {
+        Trackable.of(entity).getDataTrackers().sendInitial(player, sender);
+    }
+}

src/main/java/com/minelittlepony/unicopia/network/track/DataTracker.java

@@ -66,8 +66,7 @@ public class DataTracker {
     }
 
     @SuppressWarnings("unchecked")
-    @Nullable
-    synchronized void getDirtyPairs(List<MsgTrackedValues.TrackerEntries> output) {
+    private void updateTrackables() {
         for (var entry : persistentObjects.int2ObjectEntrySet()) {
             int key = entry.getIntKey();
             TrackableObject.Status status = entry.getValue().getStatus();
@@ -76,12 +75,23 @@ public class DataTracker {
                 dirtyIndices.add(key);
             }
         }
+    }
 
+    synchronized void getInitialPairs(List<MsgTrackedValues.TrackerEntries> output) {
+        updateTrackables();
+        output.add(new MsgTrackedValues.TrackerEntries(id, true, codecs));
+    }
+
+    @Nullable
+    synchronized void getDirtyPairs(List<MsgTrackedValues.TrackerEntries> output) {
         if (initial) {
             initial = false;
             dirtyIndices = new IntOpenHashSet();
-            output.add(new MsgTrackedValues.TrackerEntries(id, true, codecs));
-        } else if (!dirtyIndices.isEmpty()) {
+            getInitialPairs(output);
+        } else {
+            updateTrackables();
+
+            if (!dirtyIndices.isEmpty()) {
                 IntSet toSend = dirtyIndices;
                 dirtyIndices = new IntOpenHashSet();
                 List<Pair<?>> pairs = new ArrayList<>();
@@ -91,6 +101,7 @@ public class DataTracker {
                 output.add(new MsgTrackedValues.TrackerEntries(id, false, pairs));
             }
         }
+    }
 
     synchronized void load(MsgTrackedValues.TrackerEntries values) {
         if (values.wipe()) {

src/main/java/com/minelittlepony/unicopia/network/track/DataTrackerManager.java

@@ -2,6 +2,7 @@ package com.minelittlepony.unicopia.network.track;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
 import java.util.function.Supplier;
 
 import com.minelittlepony.unicopia.network.Channel;
@@ -9,6 +10,9 @@ import com.minelittlepony.unicopia.util.Tickable;
 
 import it.unimi.dsi.fastutil.objects.ObjectArrayList;
 import net.minecraft.entity.Entity;
+import net.minecraft.network.listener.ClientPlayPacketListener;
+import net.minecraft.network.packet.Packet;
+import net.minecraft.server.network.ServerPlayerEntity;
 
 public class DataTrackerManager implements Tickable {
     private final Entity entity;
@@ -45,17 +49,12 @@ public class DataTrackerManager implements Tickable {
             return;
         }
 
+        synchronized (this) {
             List<MsgTrackedValues.TrackerEntries> toTransmit = new ArrayList<>();
             List<MsgTrackedValues.TrackerObjects> objToTransmit = new ArrayList<>();
 
-        synchronized (this) {
-            for (var entry : trackers) {
-                entry.getDirtyPairs(toTransmit);
-            }
-
-            for (var entry : objectTrackers) {
-                entry.getDirtyPairs(objToTransmit);
-            }
+            for (var entry : trackers) entry.getDirtyPairs(toTransmit);
+            for (var entry : objectTrackers) entry.getDirtyPairs(objToTransmit);
 
             if (!toTransmit.isEmpty() || !objToTransmit.isEmpty()) {
                 MsgTrackedValues packet = new MsgTrackedValues(
@@ -68,6 +67,25 @@ public class DataTrackerManager implements Tickable {
         }
     }
 
+    public synchronized void sendInitial(ServerPlayerEntity player, Consumer<Packet<ClientPlayPacketListener>> sender) {
+        synchronized (this) {
+            List<MsgTrackedValues.TrackerEntries> toTransmit = new ArrayList<>();
+            List<MsgTrackedValues.TrackerObjects> objToTransmit = new ArrayList<>();
+
+            for (var entry : trackers) entry.getInitialPairs(toTransmit);
+            for (var entry : objectTrackers) entry.getInitialPairs(objToTransmit);
+
+            if (!toTransmit.isEmpty() || !objToTransmit.isEmpty()) {
+                MsgTrackedValues packet = new MsgTrackedValues(
+                        entity.getId(),
+                        objToTransmit,
+                        toTransmit
+                );
+                sender.accept(Channel.SERVER_TRACKED_ENTITY_DATA.toPacket(packet));
+            }
+        }
+    }
+
     synchronized void load(MsgTrackedValues packet) {
         for (var update : packet.updatedTrackers()) {
             DataTracker tracker = trackers.get(update.id());

src/main/java/com/minelittlepony/unicopia/network/track/ObjectTracker.java

@@ -73,6 +73,17 @@ public class ObjectTracker<T extends TrackableObject> implements NbtSerialisable
         quickAccess = Map.copyOf(trackedObjects);
     }
 
+    synchronized void getInitialPairs(List<MsgTrackedValues.TrackerObjects> output) {
+        if (!trackedObjects.isEmpty()) {
+            Map<UUID, NbtCompound> trackableCompounds = new HashMap<>();
+            quickAccess.entrySet().forEach(object -> {
+                trackableCompounds.put(object.getKey(), object.getValue().toTrackedNbt());
+            });
+
+            output.add(new MsgTrackedValues.TrackerObjects(id, Set.of(), trackableCompounds));
+        }
+    }
+
     synchronized void getDirtyPairs(List<MsgTrackedValues.TrackerObjects> output) {
         if (!trackedObjects.isEmpty()) {
             Map<UUID, NbtCompound> trackableCompounds = new HashMap<>();

src/main/java/com/minelittlepony/unicopia/network/track/Trackable.java

@@ -3,7 +3,6 @@ package com.minelittlepony.unicopia.network.track;
 import net.minecraft.entity.Entity;
 
 public interface Trackable {
-
     DataTrackerManager getDataTrackers();
 
     static Trackable of(Entity entity) {

src/main/resources/unicopia.mixin.json

@@ -51,6 +51,7 @@
     "MixinWardenEntity",
     "MixinWorld",
     "PointOfInterestTypesAccessor",
+    "server.MixinEntityTrackerEntry",
     "server.MixinPlayerManager",
     "server.MixinServerPlayerEntity",
     "server.MixinServerPlayNetworkHandler",