Add priority levels to Exit.

OpenRA.Mods.Common/Traits/Buildings/Exit.cs

@@ -32,6 +32,9 @@ namespace OpenRA.Mods.Common.Traits
 		[Desc("Number of ticks to wait before moving into the world.")]
 		public readonly int ExitDelay = 0;
 
+		[Desc("Exits with larger priorities will be used before lower priorities.")]
+		public readonly int Priority = 1;
+
 		public override object Create(ActorInitializer init) { return new Exit(init, this); }
 	}
 
@@ -46,7 +49,8 @@ namespace OpenRA.Mods.Common.Traits
 		public static Exit FirstExitOrDefault(this Actor actor, string productionType = null)
 		{
 			var all = actor.TraitsImplementing<Exit>()
-				.Where(Exts.IsTraitEnabled);
+				.Where(Exts.IsTraitEnabled)
+				.OrderBy(e => e.Info.Priority);
 
 			if (string.IsNullOrEmpty(productionType))
 				return all.FirstOrDefault(e => e.Info.ProductionTypes.Count == 0);
@@ -71,8 +75,18 @@ namespace OpenRA.Mods.Common.Traits
 			if (!allOfType.Any())
 				return null;
 
-			var shuffled = allOfType.Shuffle(world.SharedRandom);
-			return p != null ? shuffled.FirstOrDefault(p) : shuffled.First();
+			foreach (var g in allOfType.GroupBy(e => e.Info.Priority))
+			{
+				var shuffled = g.Shuffle(world.SharedRandom);
+				if (p == null)
+					return shuffled.First();
+
+				var valid = shuffled.FirstOrDefault(p);
+				if (valid != null)
+					return valid;
+			}
+
+			return null;
 		}
 	}
 }