8 files changed, 27 insertions, 5 deletions
diff --git a/src/ai/api/ai_changelog.hpp b/src/ai/api/ai_changelog.hpp
index 0ff70f9b1..af82a18e5 100644
--- a/src/ai/api/ai_changelog.hpp
+++ b/src/ai/api/ai_changelog.hpp
@@ -21,6 +21,7 @@
  * API additions:
  * \li AIBaseStation
  * \li AIBuoyList
+ * \li AIEngine::IsBuildable
  * \li AIEventCompanyAskMerger
  * \li AIIndustry::GetLastMonthTransportedPercentage
  * \li AIOrder::AIOF_GOTO_NEAREST_DEPOT
@@ -81,6 +82,10 @@
  *     For GetCargoType the first most used cargo type is returned.
  * \li AIIndustryType::GetConstructionCost() now returns -1 if the industry is
  *     neither buildable nor prospectable.
+ * \li AIEngine::IsValidEngine will now return true if you have at least one
+ *     vehicle of that type in your company, regardless if it's still buildable
+ *     or not. AIEngine::IsBuildable returns only true when you can actually
+ *     build an engine.
  *
  * \b 0.7.5
  *
diff --git a/src/ai/api/ai_engine.cpp b/src/ai/api/ai_engine.cpp
index 6416c95ff..157ee825d 100644
--- a/src/ai/api/ai_engine.cpp
+++ b/src/ai/api/ai_engine.cpp
@@ -12,6 +12,7 @@
 #include "ai_engine.hpp"
 #include "ai_cargo.hpp"
 #include "../../company_func.h"
+#include "../../company_base.h"
 #include "../../strings_func.h"
 #include "../../settings_type.h"
 #include "../../rail.h"
@@ -22,6 +23,13 @@
 /* static */ bool AIEngine::IsValidEngine(EngineID engine_id)
 {
 	const Engine *e = ::Engine::GetIfValid(engine_id);
+	return e != NULL && (HasBit(e->company_avail, _current_company) || ::Company::Get(_current_company)->num_engines[engine_id] > 0);
+
+}
+
+/* static */ bool AIEngine::IsBuildable(EngineID engine_id)
+{
+	const Engine *e = ::Engine::GetIfValid(engine_id);
 	return e != NULL && HasBit(e->company_avail, _current_company);
 }
 
diff --git a/src/ai/api/ai_engine.hpp b/src/ai/api/ai_engine.hpp
index 3d213fd3e..431f622c8 100644
--- a/src/ai/api/ai_engine.hpp
+++ b/src/ai/api/ai_engine.hpp
@@ -26,13 +26,21 @@ public:
 	static const char *GetClassName() { return "AIEngine"; }
 
 	/**
-	 * Checks whether the given engine type is valid and buildable by you.
+	 * Checks whether the given engine type is valid. An engine is valid if you
+	 * have at least one vehicle of this engine or it's currently buildable.
 	 * @param engine_id The engine to check.
 	 * @return True if and only if the engine type is valid.
 	 */
 	static bool IsValidEngine(EngineID engine_id);
 
 	/**
+	 * Checks whether the given engine type is buildable by you.
+	 * @param engine_id The engine to check.
+	 * @return True if and only if the engine type is buildable.
+	 */
+	static bool IsBuildable(EngineID engine_id);
+
+	/**
 	 * Get the name of an engine.
 	 * @param engine_id The engine to get the name of.
 	 * @pre IsValidEngine(engine_id).
diff --git a/src/ai/api/ai_engine.hpp.sq b/src/ai/api/ai_engine.hpp.sq
index 78f9a1c06..594f7bd5e 100644
--- a/src/ai/api/ai_engine.hpp.sq
+++ b/src/ai/api/ai_engine.hpp.sq
@@ -27,6 +27,7 @@ void SQAIEngine_Register(Squirrel *engine)
 	SQAIEngine.AddConstructor<void (AIEngine::*)(), 1>(engine, "x");
 
 	SQAIEngine.DefSQStaticMethod(engine, &AIEngine::IsValidEngine,        "IsValidEngine",        2, ".i");
+	SQAIEngine.DefSQStaticMethod(engine, &AIEngine::IsBuildable,          "IsBuildable",          2, ".i");
 	SQAIEngine.DefSQStaticMethod(engine, &AIEngine::GetName,              "GetName",              2, ".i");
 	SQAIEngine.DefSQStaticMethod(engine, &AIEngine::GetCargoType,         "GetCargoType",         2, ".i");
 	SQAIEngine.DefSQStaticMethod(engine, &AIEngine::CanRefitCargo,        "CanRefitCargo",        3, ".ii");
diff --git a/src/ai/api/ai_group.cpp b/src/ai/api/ai_group.cpp
index c9d3795cb..0aad40cf5 100644
--- a/src/ai/api/ai_group.cpp
+++ b/src/ai/api/ai_group.cpp
@@ -114,7 +114,7 @@
 /* static */ bool AIGroup::SetAutoReplace(GroupID group_id, EngineID engine_id_old, EngineID engine_id_new)
 {
 	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_ALL);
-	EnforcePrecondition(false, AIEngine::IsValidEngine(engine_id_new));
+	EnforcePrecondition(false, AIEngine::IsBuildable(engine_id_new));
 
 	return AIObject::DoCommand(0, group_id << 16, (engine_id_new << 16) | engine_id_old, CMD_SET_AUTOREPLACE);
 }
diff --git a/src/ai/api/ai_group.hpp b/src/ai/api/ai_group.hpp
index a26c5fb0d..422f2962a 100644
--- a/src/ai/api/ai_group.hpp
+++ b/src/ai/api/ai_group.hpp
@@ -149,7 +149,7 @@ public:
 	 * @param engine_id_old The engine id to start replacing.
 	 * @param engine_id_new The engine id to replace with.
 	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL.
-	 * @pre AIEngine.IsValidEngine(engine_id_new).
+	 * @pre AIEngine.IsBuildable(engine_id_new).
 	 * @note To stop autoreplacing engine_id_old, call StopAutoReplace(group_id, engine_id_old).
 	 */
 	static bool SetAutoReplace(GroupID group_id, EngineID engine_id_old, EngineID engine_id_new);
diff --git a/src/ai/api/ai_vehicle.cpp b/src/ai/api/ai_vehicle.cpp
index c05f67909..03f39bae6 100644
--- a/src/ai/api/ai_vehicle.cpp
+++ b/src/ai/api/ai_vehicle.cpp
@@ -64,7 +64,7 @@
 
 /* static */ VehicleID AIVehicle::BuildVehicle(TileIndex depot, EngineID engine_id)
 {
-	EnforcePrecondition(INVALID_VEHICLE, AIEngine::IsValidEngine(engine_id));
+	EnforcePrecondition(INVALID_VEHICLE, AIEngine::IsBuildable(engine_id));
 
 	::VehicleType type = ::Engine::Get(engine_id)->type;
 
diff --git a/src/ai/api/ai_vehicle.hpp b/src/ai/api/ai_vehicle.hpp
index 4041287a7..049ee8ade 100644
--- a/src/ai/api/ai_vehicle.hpp
+++ b/src/ai/api/ai_vehicle.hpp
@@ -300,7 +300,7 @@ public:
 	 * @param engine_id The engine to use for this vehicle.
 	 * @pre The tile at depot has a depot that can build the engine and
 	 *   is owned by you.
-	 * @pre IsValidEngine(engine_id).
+	 * @pre AIEngine::IsBuildable(engine_id).
 	 * @exception AIVehicle::ERR_VEHICLE_TOO_MANY
 	 * @exception AIVehicle::ERR_VEHICLE_BUILD_DISABLED
 	 * @exception AIVehicle::ERR_VEHICLE_WRONG_DEPOT