Replace default/fallback servers with a server priority list.

api/src/main/java/net/md_5/bungee/api/config/ListenerInfo.java

@@ -1,8 +1,11 @@
 package net.md_5.bungee.api.config;
 
 import java.net.InetSocketAddress;
+import java.util.List;
 import java.util.Map;
+import lombok.AccessLevel;
 import lombok.Data;
+import lombok.Getter;
 
 /**
  * Class representing the configuration of a server listener. Used for allowing
@@ -29,14 +32,10 @@ public class ListenerInfo
      */
     private final int tabListSize;
     /**
-     * Name of the server which users will be taken to by default.
+     * List of servers in order of join attempt. First attempt is the first
+     * element, second attempt is the next element, etc etc.
      */
-    private final String defaultServer;
+    private final List<String> serverPriority;
-    /**
-     * Name of the server which users will be taken when current server goes
-     * down.
-     */
-    private final String fallbackServer;
     /**
      * Whether reconnect locations will be used, or else the user is simply
      * transferred to the default server on connect.
@@ -68,4 +67,29 @@ public class ListenerInfo
      * Whether to enable udp query.
      */
     private final boolean queryEnabled;
+
+    /**
+     * Gets the highest priority server to join.
+     *
+     * @return default server
+     * @deprecated replaced by {@link #serverPriority}
+     */
+    @Deprecated
+    public String getDefaultServer()
+    {
+        return serverPriority.get( 0 );
+    }
+
+    /**
+     * Gets the second highest priority server to join, or else the highest
+     * priority.
+     *
+     * @return fallback server
+     * @deprecated replaced by {@link #serverPriority}
+     */
+    @Deprecated
+    public String getFallbackServer()
+    {
+        return ( serverPriority.size() > 1 ) ? serverPriority.get( 1 ) : getDefaultServer();
+    }
 }

proxy/src/main/java/net/md_5/bungee/conf/YamlConfig.java

@@ -7,12 +7,14 @@ import java.io.FileWriter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.InetSocketAddress;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.logging.Level;
 import lombok.RequiredArgsConstructor;
@@ -126,6 +128,34 @@ public class YamlConfig implements ConfigurationAdapter
         }
     }
 
+    @SuppressWarnings("unchecked")
+    private void set(String path, Object val, Map submap)
+    {
+        int index = path.indexOf( '.' );
+        if ( index == -1 )
+        {
+            if ( val == null )
+            {
+                submap.remove( path );
+            } else
+            {
+                submap.put( path, val );
+            }
+            save();
+        } else
+        {
+            String first = path.substring( 0, index );
+            String second = path.substring( index + 1, path.length() );
+            Map sub = (Map) submap.get( first );
+            if ( sub == null )
+            {
+                sub = new LinkedHashMap();
+                submap.put( first, sub );
+            }
+            set( second, val, sub );
+        }
+    }
+
     private void save()
     {
         try
@@ -200,8 +230,6 @@ public class YamlConfig implements ConfigurationAdapter
             motd = ChatColor.translateAlternateColorCodes( '&', motd );
 
             int maxPlayers = get( "max_players", 1, val );
-            String defaultServer = get( "default_server", "lobby", val );
-            String fallbackServer = get( "fallback_server", defaultServer, val );
             boolean forceDefault = get( "force_default_server", false, val );
             String host = get( "host", "0.0.0.0:25577", val );
             int tabListSize = get( "tab_size", 60, val );
@@ -219,7 +247,31 @@ public class YamlConfig implements ConfigurationAdapter
             boolean query = get( "query_enabled", false, val );
             int queryPort = get( "query_port", 25577, val );
 
-            ListenerInfo info = new ListenerInfo( address, motd, maxPlayers, tabListSize, defaultServer, fallbackServer, forceDefault, forced, value.toString(), setLocalAddress, pingPassthrough, queryPort, query );
+            List<String> serverPriority = new ArrayList<>( get( "priorities", Collections.EMPTY_LIST, val ) );
+
+            // Default server list migration
+            // TODO: Remove from submap
+            String defaultServer = get( "default_server", null, val );
+            String fallbackServer = get( "fallback_server", null, val );
+            if ( defaultServer != null )
+            {
+                serverPriority.add( defaultServer );
+                set( "default_server", null, val );
+            }
+            if ( fallbackServer != null )
+            {
+                serverPriority.add( fallbackServer );
+                set( "fallback_server", null, val );
+            }
+
+            // Add defaults if required
+            if ( serverPriority.isEmpty() )
+            {
+                serverPriority.add( "lobby" );
+            }
+            set( "priorities", serverPriority, val );
+
+            ListenerInfo info = new ListenerInfo( address, motd, maxPlayers, tabListSize, serverPriority, forceDefault, forced, value.toString(), setLocalAddress, pingPassthrough, queryPort, query );
             ret.add( info );
         }