Add an advancement trigger for when a player has a stage.

  "criteria": {
    "get_the_stage": {
      "trigger": "gamestages:has_stage",
      "conditions": {
        "stage": "target_stage_name"
      }
    }
  }

Author: Darkhax

src/main/java/net/darkhax/gamestages/GameStageHelper.java

@@ -1,5 +1,6 @@
 package net.darkhax.gamestages;
 
+import net.darkhax.gamestages.advancement.HasStageTrigger;
 import net.darkhax.gamestages.data.GameStageSaveHandler;
 import net.darkhax.gamestages.data.IStageData;
 import net.darkhax.gamestages.event.GameStageEvent;
@@ -303,6 +304,10 @@ public static void syncPlayer (ServerPlayer player) {
 
             GameStages.LOG.debug("Syncing {} stages for {}.", info.getStages().size(), player.getName());
             GameStages.NETWORK.syncPlayerStages(player, new MessageStages(info.getStages()));
+
+            for (String stage : info.getStages()) {
+                HasStageTrigger.INSTANCE.trigger(player, stage);
+            }
         }
     }
 }

src/main/java/net/darkhax/gamestages/GameStages.java

@@ -1,69 +1,77 @@
 package net.darkhax.gamestages;
 
+import net.darkhax.gamestages.advancement.HasStageTrigger;
 import net.darkhax.gamestages.command.GameStageCommands;
 import net.darkhax.gamestages.data.GameStageSaveHandler;
 import net.darkhax.gamestages.data.IStageData;
 import net.darkhax.gamestages.packet.GameStagesPacketHandler;
 import net.minecraft.ChatFormatting;
+import net.minecraft.advancements.CriteriaTriggers;
 import net.minecraft.client.Minecraft;
 import net.minecraftforge.api.distmarker.Dist;
 import net.minecraftforge.api.distmarker.OnlyIn;
 import net.minecraftforge.client.event.CustomizeGuiOverlayEvent;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.AddReloadListenerEvent;
 import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.event.lifecycle.FMLCommonSetupEvent;
+import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
 import net.minecraftforge.fml.loading.FMLEnvironment;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
 @Mod(GameStages.MOD_ID)
 public class GameStages {
-    
+
     public static final String MOD_ID = "gamestages";
     public static final Logger LOG = LogManager.getLogger("Game Stages");
     public static final GameStagesPacketHandler NETWORK = new GameStagesPacketHandler();
-    
+
     public GameStages() {
 
         GameStageSaveHandler.reloadFakePlayers();
         GameStageSaveHandler.reloadKnownStages();
         GameStageCommands.initializeCommands();
-        
         if (FMLEnvironment.dist.isClient()) {
-            
             MinecraftForge.EVENT_BUS.addListener(this::onF3Text);
         }
-        
         MinecraftForge.EVENT_BUS.addListener(this::registerReloadListeners);
+        FMLJavaModLoadingContext.get().getModEventBus().addListener(this::setup);
+    }
+
+    private void setup(final FMLCommonSetupEvent event) {
+        event.enqueueWork(() -> {
+            CriteriaTriggers.register(HasStageTrigger.INSTANCE);
+        });
     }
-    
+
     private void registerReloadListeners(AddReloadListenerEvent event) {
-        
+
         event.addListener(new GameStageReloader());
     }
-    
+
     @OnlyIn(Dist.CLIENT)
-    private void onF3Text (CustomizeGuiOverlayEvent.DebugText event) {
-        
+    private void onF3Text(CustomizeGuiOverlayEvent.DebugText event) {
+
         final Minecraft mc = Minecraft.getInstance();
-        
+
         if (mc.options.renderDebug) {
-            
+
             if (mc.player != null && mc.player.isShiftKeyDown()) {
-                
+
                 final IStageData data = GameStageHelper.getPlayerData(mc.player);
-                
+
                 if (data != null) {
-                    
+
                     event.getRight().add(ChatFormatting.GOLD + ChatFormatting.UNDERLINE.toString() + "GameStages");
                     event.getRight().add("Count: " + data.getStages().size());
                     event.getRight().add("Type: " + data.getClass().getName());
                     event.getRight().add("Stages: " + data.getStages().toString());
                 }
             }
-            
+
             else {
-                
+
                 event.getRight().add(ChatFormatting.GOLD + ChatFormatting.UNDERLINE.toString() + "GameStages [Shift]");
             }
         }

src/main/java/net/darkhax/gamestages/advancement/HasStageTrigger.java

@@ -0,0 +1,49 @@
+package net.darkhax.gamestages.advancement;
+
+import com.google.gson.JsonObject;
+import net.darkhax.gamestages.GameStageHelper;
+import net.darkhax.gamestages.GameStages;
+import net.minecraft.advancements.critereon.AbstractCriterionTriggerInstance;
+import net.minecraft.advancements.critereon.ContextAwarePredicate;
+import net.minecraft.advancements.critereon.DeserializationContext;
+import net.minecraft.advancements.critereon.SerializationContext;
+import net.minecraft.advancements.critereon.SimpleCriterionTrigger;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.server.level.ServerPlayer;
+
+public class HasStageTrigger extends SimpleCriterionTrigger<HasStageTrigger.Instance> {
+
+    public static final ResourceLocation TRIGGER_ID = new ResourceLocation(GameStages.MOD_ID, "has_stage");
+    public static final HasStageTrigger INSTANCE = new HasStageTrigger();
+
+    public void trigger(ServerPlayer player, String stage) {
+        this.trigger(player, predicate -> GameStageHelper.hasAllOf(player, stage));
+    }
+
+    @Override
+    protected Instance createInstance(JsonObject json, ContextAwarePredicate playerContext, DeserializationContext context) {
+        return new Instance(playerContext, json.get("stage").getAsString());
+    }
+
+    @Override
+    public ResourceLocation getId() {
+        return TRIGGER_ID;
+    }
+
+    public static class Instance extends AbstractCriterionTriggerInstance {
+
+        private final String stage;
+
+        public Instance(ContextAwarePredicate context, String stage) {
+            super(TRIGGER_ID, context);
+            this.stage = stage;
+        }
+
+        @Override
+        public JsonObject serializeToJson(SerializationContext context) {
+            final JsonObject json = super.serializeToJson(context);
+            json.addProperty("stage", this.stage);
+            return json;
+        }
+    }
+}