2 files changed, 94 insertions, 0 deletions
diff --git a/src/main/java/com/keuin/kbackupfabric/notification/DistinctNotifiable.java b/src/main/java/com/keuin/kbackupfabric/notification/DistinctNotifiable.java
new file mode 100644
index 0000000..b44bfce
--- /dev/null
+++ b/src/main/java/com/keuin/kbackupfabric/notification/DistinctNotifiable.java
@@ -0,0 +1,45 @@
+package com.keuin.kbackupfabric.notification;
+
+import net.minecraft.network.MessageType;
+import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.text.Text;
+
+/**
+ * Decouple from ServerPlayerEntity, in case further migration to other APIs.
+ */
+public interface DistinctNotifiable {
+
+    /**
+     * Does the receiver has privilege to receive some special message.
+     */
+    boolean isPrivileged();
+
+    void notify(Text text);
+
+    /**
+     * Get an unique, non-null object that identifies this notifiable instance.
+     * The identifier must be immutable and implement their own equals method.
+     *
+     * @return the identifier.
+     */
+    Object getIdentifier();
+
+    static DistinctNotifiable fromServerPlayerEntity(ServerPlayerEntity serverPlayerEntity) {
+        return new DistinctNotifiable() {
+            @Override
+            public boolean isPrivileged() {
+                return serverPlayerEntity.server.getPermissionLevel(serverPlayerEntity.getGameProfile()) >= serverPlayerEntity.server.getOpPermissionLevel();
+            }
+
+            @Override
+            public void notify(Text text) {
+                serverPlayerEntity.sendChatMessage(text, MessageType.SYSTEM);
+            }
+
+            @Override
+            public Object getIdentifier() {
+                return serverPlayerEntity.getUuid();
+            }
+        };
+    }
+}
diff --git a/src/main/java/com/keuin/kbackupfabric/notification/NotificationManager.java b/src/main/java/com/keuin/kbackupfabric/notification/NotificationManager.java
new file mode 100644
index 0000000..96ecf41
--- /dev/null
+++ b/src/main/java/com/keuin/kbackupfabric/notification/NotificationManager.java
@@ -0,0 +1,49 @@
+package com.keuin.kbackupfabric.notification;
+
+import com.keuin.kbackupfabric.metadata.BackupMetadata;
+import com.keuin.kbackupfabric.metadata.MetadataHolder;
+import com.keuin.kbackupfabric.util.DateUtil;
+import net.minecraft.text.LiteralText;
+import net.minecraft.text.Style;
+import net.minecraft.util.Formatting;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Notify some users when the server has been restored to a backup.
+ */
+public class NotificationManager {
+
+    public static final NotificationManager INSTANCE = new NotificationManager();
+
+    private final Set<Object> notified = new HashSet<>();
+
+    private NotificationManager() {
+    }
+
+    public void notifyPlayer(DistinctNotifiable distinctNotifiable) {
+        Object identifier = distinctNotifiable.getIdentifier();
+        if (distinctNotifiable.isPrivileged() && !notified.contains(identifier)) {
+            notified.add(identifier);
+            notify(distinctNotifiable);
+        }
+    }
+
+    /**
+     * Just notify if necessary. It will not update the set.
+     */
+    private void notify(DistinctNotifiable notifiable) {
+        if (MetadataHolder.hasMetadata()) {
+            BackupMetadata backup = MetadataHolder.getMetadata();
+            notifiable.notify(
+                    new LiteralText("The server has been restored to backup ")
+                            .append(new LiteralText("[" + backup.getBackupName() + "]").setStyle(new Style().setColor(Formatting.GREEN)))
+                            .append(new LiteralText(" (created at "))
+                            .append(new LiteralText("[" + DateUtil.fromEpochMillis(backup.getBackupTime()) + "]").setStyle(new Style().setColor(Formatting.GREEN)))
+                            .append(new LiteralText(")"))
+            );
+        }
+    }
+
+}