add permission-based rankups

src/main/java/sh/okx/rankup/hook/PermissionManager.java

@@ -27,4 +27,8 @@ public class PermissionManager {
     }
     return new VaultPermissionProvider(provider);
   }
+
+  public PermissionProvider permissionOnlyProvider() {
+    return new PermissionPermissionProvider();
+  }
 }

src/main/java/sh/okx/rankup/hook/PermissionPermissionProvider.java

@@ -0,0 +1,32 @@
+package sh.okx.rankup.hook;
+
+import java.util.UUID;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Player;
+
+public class PermissionPermissionProvider implements PermissionProvider {
+
+  @Override
+  public boolean inGroup(UUID uuid, String group) {
+    Player player = getPlayer(uuid);
+    return player.hasPermission("rankup.rank." + group);
+  }
+
+  @Override
+  public void addGroup(UUID uuid, String group) {
+    // no-op
+  }
+
+  @Override
+  public void removeGroup(UUID uuid, String group) {
+    // no-op
+  }
+
+  private Player getPlayer(UUID uuid) {
+    Player player = Bukkit.getPlayer(uuid);
+    if (player == null) {
+      throw new IllegalArgumentException("Player not online!");
+    }
+    return player;
+  }
+}