From d20b3c4e584da772c6888cc87b25fee14bd2c134 Mon Sep 17 00:00:00 2001
From: SomeTroglodyte <63000004+SomeTroglodyte@users.noreply.github.com>
Date: Thu, 13 May 2021 19:25:16 +0200
Subject: [PATCH] Fix crash when a mod allows a citadel >1 tile outside borders
 (#3923)

* Fix crash when a mod allows a citadel >1 tile outside borders

* Fix crash when a mod allows a citadel outside borders - no cities
---
 core/src/com/unciv/logic/map/TileInfo.kt            |  3 ++-
 .../com/unciv/ui/worldscreen/unit/UnitActions.kt    | 13 ++++++++++---
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/core/src/com/unciv/logic/map/TileInfo.kt b/core/src/com/unciv/logic/map/TileInfo.kt
index a7ed12da6b..24482d40b3 100644
--- a/core/src/com/unciv/logic/map/TileInfo.kt
+++ b/core/src/com/unciv/logic/map/TileInfo.kt
@@ -336,7 +336,8 @@ open class TileInfo {
             getOwner() != civInfo && !(
                     improvement.hasUnique("Can be built outside your borders")
                             // citadel can be built only next to or within own borders
-                            || improvement.hasUnique("Can be built just outside your borders") && neighbors.any { it.getOwner() == civInfo }
+                            || improvement.hasUnique("Can be built just outside your borders")
+                                && neighbors.any { it.getOwner() == civInfo } && !civInfo.cities.isEmpty()
                     ) -> false
             improvement.uniqueObjects.any {
                 it.placeholderText == "Obsolete with []" && civInfo.tech.isResearched(it.params[0])
diff --git a/core/src/com/unciv/ui/worldscreen/unit/UnitActions.kt b/core/src/com/unciv/ui/worldscreen/unit/UnitActions.kt
index 35ece6ec5b..691f27761e 100644
--- a/core/src/com/unciv/ui/worldscreen/unit/UnitActions.kt
+++ b/core/src/com/unciv/ui/worldscreen/unit/UnitActions.kt
@@ -360,19 +360,26 @@ object UnitActions {
 
     private fun takeOverTilesAround(unit: MapUnit) {
         // This method should only be called for a citadel - therefore one of the neighbour tile
-        // must belong to unit's civ, so minByOrNull will be never `null`. Thiss
+        // must belong to unit's civ, so minByOrNull in the nearestCity formula should be never `null`.
+        // That is, unless a mod does not specify the proper unique - then fallbackNearestCity will take over.
 
         fun priority(tile: TileInfo): Int { // helper calculates priority (lower is better): distance plus razing malus
             val city = tile.getCity()!!       // !! assertion is guaranteed by the outer filter selector.
             return city.getCenterTile().aerialDistanceTo(tile) +
                     (if (city.isBeingRazed) 5 else 0)
         }
+        fun fallbackNearestCity(unit: MapUnit) =
+            unit.civInfo.cities.minByOrNull {
+               it.getCenterTile().aerialDistanceTo(unit.currentTile) +
+                   (if (it.isBeingRazed) 5 else 0)
+            }!!
 
         // In the rare case more than one city owns tiles neighboring the citadel
         // this will prioritize the nearest one not being razed
-        val nearestCity = unit.currentTile.neighbors
+        var nearestCity = unit.currentTile.neighbors
             .filter { it.getOwner() == unit.civInfo }
-            .minByOrNull { priority(it) }!!.getCity()!!
+            .minByOrNull { priority(it) }?.getCity()
+            ?: fallbackNearestCity(unit)
 
         // capture all tiles which do not belong to unit's civ and are not enemy cities
         // we use getTilesInDistance here, not neighbours to include the current tile as well