allow other plugins to register requirements and operaitons

src/main/java/sh/okx/rankup/Rankup.java

@@ -152,11 +152,13 @@ public class Rankup extends JavaPlugin {
   private void loadConfigs() {
     messages = loadConfig("messages.yml");
     config = loadConfig("config.yml");
-    refreshRanks();
+    Bukkit.getScheduler().scheduleSyncDelayedTask(this, this::refreshRanks);
   }
 
   public void refreshRanks() {
     registerRequirements();
+    Bukkit.getPluginManager().callEvent(new RankupRegisterEvent(this));
+
     rankups = new Rankups(this, loadConfig("rankups.yml"));
     if(config.getBoolean("prestige")) {
       prestiges = new Prestiges(this, loadConfig("prestiges.yml"));
@@ -191,8 +193,6 @@ public class Rankup extends JavaPlugin {
     operationRegistry.addOperation("none", new NoneOperation());
     operationRegistry.addOperation("one", new OneOperation());
     operationRegistry.addOperation("any", new AnyOperation());
-
-    Bukkit.getPluginManager().callEvent(new RankupRegisterEvent(this));
   }
 
   private void setupPermissions() {

src/main/java/sh/okx/rankup/RankupRegisterEvent.java

@@ -4,7 +4,9 @@ import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 import org.bukkit.event.Event;
 import org.bukkit.event.HandlerList;
+import sh.okx.rankup.requirements.Operation;
 import sh.okx.rankup.requirements.OperationRegistry;
+import sh.okx.rankup.requirements.Requirement;
 import sh.okx.rankup.requirements.RequirementRegistry;
 
 /**
@@ -27,6 +29,14 @@ public class RankupRegisterEvent extends Event {
     return plugin.getOperationRegistry();
   }
 
+  public void addRequirement(Requirement requirement) {
+    plugin.getRequirementRegistry().addRequirement(requirement);
+  }
+
+  public void addOperation(String name, Operation operation) {
+    plugin.getOperationRegistry().addOperation(name, operation);
+  }
+
   @Override
   public HandlerList getHandlers() {
     return handlers;

src/main/java/sh/okx/rankup/requirements/Operation.java

@@ -2,6 +2,6 @@ package sh.okx.rankup.requirements;
 
 import java.util.List;
 
-public abstract class Operation {
-  public abstract boolean check(List<Boolean> booleans);
+public interface Operation {
+  boolean check(List<Boolean> booleans);
 }

src/main/java/sh/okx/rankup/requirements/ReducerOperation.java

@@ -2,7 +2,7 @@ package sh.okx.rankup.requirements;
 
 import java.util.List;
 
-public abstract class ReducerOperation extends Operation {
+public abstract class ReducerOperation implements Operation {
   public abstract boolean check(boolean a, boolean b);
 
   @Override