移除canPlayOffline()

HMCLCore/src/main/java/org/jackhuang/hmcl/auth/Account.java

@@ -20,6 +20,7 @@ package org.jackhuang.hmcl.auth;
 import org.jackhuang.hmcl.util.ToStringBuilder;
 
 import java.util.Map;
+import java.util.Optional;
 import java.util.UUID;
 
 /**
@@ -56,13 +57,11 @@ public abstract class Account {
      */
     public abstract AuthInfo logInWithPassword(String password) throws AuthenticationException;
 
-    public abstract boolean canPlayOffline();
-
     /**
      * Play offline.
      * @return the specific offline player's info.
      */
-    public abstract AuthInfo playOffline();
+    public abstract Optional<AuthInfo> playOffline();
 
     public abstract Map<Object, Object> toStorage();
 

HMCLCore/src/main/java/org/jackhuang/hmcl/auth/offline/OfflineAccount.java

@@ -26,6 +26,7 @@ import org.jackhuang.hmcl.util.UUIDTypeAdapter;
 
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.UUID;
 
 import static org.jackhuang.hmcl.util.Lang.mapOf;
@@ -80,13 +81,8 @@ public class OfflineAccount extends Account {
     }
 
     @Override
-    public boolean canPlayOffline() {
-        return false;
-    }
-
-    @Override
-    public AuthInfo playOffline() {
-        throw new IllegalStateException();
+    public Optional<AuthInfo> playOffline() {
+        return Optional.empty();
     }
 
     @Override

HMCLCore/src/main/java/org/jackhuang/hmcl/auth/yggdrasil/YggdrasilAccount.java

@@ -103,16 +103,11 @@ public class YggdrasilAccount extends Account {
     }
 
     @Override
-    public boolean canPlayOffline() {
-        return isLoggedIn() && session.getSelectedProfile() != null && !canPlayOnline();
-    }
+    public Optional<AuthInfo> playOffline() {
+        if (isLoggedIn() && session.getSelectedProfile() != null && !canPlayOnline())
+            return Optional.of(session.toAuthInfo());
 
-    @Override
-    public AuthInfo playOffline() {
-        if (!canPlayOffline())
-            throw new IllegalStateException("Current account " + this + " cannot play offline.");
-
-        return session.toAuthInfo();
+        return Optional.empty();
     }
 
     @Override