Add complete offline-mode support

common/src/main/java/me/lucko/luckperms/utils/LPConfiguration.java

@@ -61,6 +61,10 @@ public abstract class LPConfiguration<T extends LuckPermsPlugin> {
         return getBoolean("include-global", defaultIncludeGlobal);
     }
 
+    public boolean getOnlineMode() {
+        return getBoolean("online-mode", true);
+    }
+
     public String getDatabaseValue(String value) {
         return getString("sql." + value, null);
     }

common/src/main/java/me/lucko/luckperms/utils/UuidCache.java

@@ -0,0 +1,38 @@
+package me.lucko.luckperms.utils;
+
+import lombok.Getter;
+
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class UuidCache {
+
+    private Map<String, UUID> cache;
+
+    @Getter
+    private final boolean onlineMode;
+
+    public UuidCache(boolean onlineMode) {
+        this.onlineMode = onlineMode;
+
+        if (!onlineMode) {
+            cache = new ConcurrentHashMap<>();
+        }
+    }
+
+    public UUID getUUID(String name, UUID fallback) {
+        return onlineMode ? fallback : (cache.containsKey(name) ? cache.get(name) : fallback);
+    }
+
+    public void addToCache(String name, UUID uuid) {
+        if (onlineMode) return;
+        cache.put(name, uuid);
+    }
+
+    public void clearCache(String name) {
+        if (onlineMode) return;
+        cache.remove(name);
+    }
+
+}