Add Server.MapPool setting for dedicated servers.

This takes a list of map UIDs which may be locally installed or hosted
on the resource center. If any maps aren't found, startup will be
delayed by up to 10 seconds while it attempts to query the resource
center.

OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs

@@ -11,12 +11,15 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using OpenRA.Mods.Common.Traits;
 using OpenRA.Mods.Common.Widgets.Logic;
 using OpenRA.Network;
 using OpenRA.Primitives;
 using OpenRA.Server;
+using OpenRA.Support;
 using OpenRA.Traits;
 using S = OpenRA.Server.Server;
 
@@ -570,6 +573,12 @@ namespace OpenRA.Mods.Common.Server
 					return true;
 				}
 
+				if (server.MapPool != null && !server.MapPool.Contains(s))
+				{
+					QueryFailed();
+					return true;
+				}
+
 				var lastMap = server.LobbyInfo.GlobalSettings.Map;
 				void SelectMap(MapPreview map)
 				{
@@ -659,8 +668,6 @@ namespace OpenRA.Mods.Common.Server
 					}
 				}
 
-				void QueryFailed() => server.SendLocalizedMessageTo(conn, UnknownMap);
-
 				var m = server.ModData.MapCache[s];
 				if (m.Status == MapStatus.Available || m.Status == MapStatus.DownloadAvailable)
 					SelectMap(m);
@@ -682,6 +689,8 @@ namespace OpenRA.Mods.Common.Server
 
 				return true;
 			}
+
+			void QueryFailed() => server.SendLocalizedMessageTo(conn, UnknownMap);
 		}
 
 		static bool Option(S server, Connection conn, Session.Client client, string s)
@@ -1227,16 +1236,68 @@ namespace OpenRA.Mods.Common.Server
 			}
 		}
 
+		static void InitializeMapPool(S server)
+		{
+			if (server.Type != ServerType.Dedicated)
+				return;
+
+			var mapCache = server.ModData.MapCache;
+			if (server.Settings.MapPool.Length > 0)
+				server.MapPool = server.Settings.MapPool.ToHashSet();
+			else if (!server.Settings.QueryMapRepository)
+				server.MapPool = mapCache
+					.Where(p => p.Status == MapStatus.Available && p.Visibility.HasFlag(MapVisibility.Lobby))
+					.Select(p => p.Uid)
+					.ToHashSet();
+			else
+				return;
+
+			var unknownMaps = server.MapPool.Where(server.MapIsUnknown);
+			if (server.Settings.QueryMapRepository && unknownMaps.Any())
+			{
+				Log.Write("server", $"Querying Resource Center for information on {unknownMaps.Count()} maps...");
+
+				// Query any missing maps and wait up to 10 seconds for a response
+				// Maps that have not resolved will not be valid for the initial map choice
+				var mapRepository = server.ModData.Manifest.Get<WebServices>().MapRepository;
+				mapCache.QueryRemoteMapDetails(mapRepository, unknownMaps);
+
+				var searchingMaps = server.MapPool.Where(uid => mapCache[uid].Status == MapStatus.Searching);
+				var stopwatch = Stopwatch.StartNew();
+				while (searchingMaps.Any() && stopwatch.ElapsedMilliseconds < 10000)
+					Thread.Sleep(100);
+			}
+
+			if (unknownMaps.Any())
+				Log.Write("server", "Failed to resolve maps: " + unknownMaps.JoinWith(", "));
+		}
+
+		static string ChooseInitialMap(S server)
+		{
+			if (server.MapIsKnown(server.Settings.Map))
+				return server.Settings.Map;
+
+			if (server.MapPool == null)
+				return server.ModData.MapCache.ChooseInitialMap(server.Settings.Map, new MersenneTwister());
+
+			return server.MapPool
+				.Where(server.MapIsKnown)
+				.RandomOrDefault(new MersenneTwister());
+		}
+
 		public void ServerStarted(S server)
 		{
 			lock (server.LobbyInfo)
 			{
-				// Remote maps are not supported for the initial map
-				var uid = server.LobbyInfo.GlobalSettings.Map;
-				server.Map = server.ModData.MapCache[uid];
-				if (server.Map.Status != MapStatus.Available)
-					throw new InvalidOperationException($"Map {uid} not found");
+				InitializeMapPool(server);
 
+				var uid = ChooseInitialMap(server);
+				if (string.IsNullOrEmpty(uid))
+					throw new InvalidOperationException("Unable to resolve a valid initial map");
+
+				server.LobbyInfo.GlobalSettings.Map = server.Settings.Map = uid;
+				server.Map = server.ModData.MapCache[uid];
+				server.LobbyInfo.GlobalSettings.MapStatus = server.MapStatusCache[server.Map];
 				server.LobbyInfo.Slots = server.Map.Players.Players
 					.Select(p => MakeSlotFromPlayerReference(p.Value))
 					.Where(s => s != null)