Fix lone faction leader validation (#8691)

src/main/scala/net/eagle0/eagle/ai/MidGameAIClient.scala

@@ -35,7 +35,7 @@ import net.eagle0.eagle.model.state.command.common.{DiplomacyOptionType, Improve
 import net.eagle0.eagle.model.state.command.selected.CombatUnit
 import net.eagle0.eagle.model.state.command.selected.SelectedCommand.{DiplomacySelected, MarchSelected, ReconSelected}
 import net.eagle0.eagle.model.state.date.Date.given
-import net.eagle0.eagle.model.state.faction.FactionRelationship as FactionRelationshipC
+import net.eagle0.eagle.model.state.faction.{FactionRelationship as FactionRelationshipC, FactionT}
 import net.eagle0.eagle.model.state.game_state.GameState
 import net.eagle0.eagle.model.state.province.ProvinceT
 import net.eagle0.eagle.model.view.battalion.BattalionView as BattalionViewC
@@ -45,17 +45,22 @@ object MidGameAIClient {
   private val SmallFactionProvinceCountForBorderDevelopment = 2
   private val BorderDefenseConfidenceRatio                  = 1.0
 
+  private[ai] def hasLoneFactionLeader(
+      province: ProvinceT,
+      factions: Vector[FactionT]
+  ): Boolean =
+    province.rulingFactionHeroIds match {
+      case Vector(heroId) => FactionUtils.isFactionLeader(heroId, factions)
+      case _              => false
+    }
+
   private def validateNoFactionLeaderAlone(
       gs: GameState,
       factionId: FactionId
   ): Unit =
     FactionUtils
       .provinces(factionId, gs.provinces.values.toVector)
-      .filter { province =>
-        province.rulingFactionHeroIds.forall(
-          FactionUtils.isFactionLeader(_, gs.factions.values.toVector)
-        )
-      }
+      .filter(hasLoneFactionLeader(_, gs.factions.values.toVector))
       .foreach { province =>
         val currentDate = gs.currentDate
         println(

src/test/scala/net/eagle0/eagle/ai/MidGameAIClientTest.scala

@@ -66,6 +66,43 @@ class MidGameAIClientTest extends AnyFlatSpec with Matchers with BeforeAndAfterE
   val leaderId      = 58
   val hubProvinceId = 4
 
+  "hasLoneFactionLeader" should "only match a province containing exactly one faction leader" in {
+    val faction = FactionC(
+      id = factionId,
+      factionHeadId = leaderId,
+      name = "",
+      leaderIds = Vector(leaderId, leaderId + 1)
+    )
+
+    def provinceWithHeroes(heroIds: HeroId*): ProvinceC =
+      ProvinceC(id = hubProvinceId, rulingFactionHeroIds = heroIds.toVector)
+
+    MidGameAIClient
+      .hasLoneFactionLeader(
+        provinceWithHeroes(),
+        Vector(faction)
+      )
+      .shouldBe(false)
+    MidGameAIClient
+      .hasLoneFactionLeader(
+        provinceWithHeroes(leaderId),
+        Vector(faction)
+      )
+      .shouldBe(true)
+    MidGameAIClient
+      .hasLoneFactionLeader(
+        provinceWithHeroes(leaderId, leaderId + 1),
+        Vector(faction)
+      )
+      .shouldBe(false)
+    MidGameAIClient
+      .hasLoneFactionLeader(
+        provinceWithHeroes(leaderId + 2),
+        Vector(faction)
+      )
+      .shouldBe(false)
+  }
+
   // Helper methods to create maps from objects
   private def mapifyProvinces(provinces: ProvinceT*): Map[ProvinceId, ProvinceT] =
     provinces.map(p => p.id -> p).toMap