Invalid trade requests (e.g. giving a city that isn't yours anymore or resources you no longer own) are discarded at the beginning of the civ's turn

android/assets/jsons/Translations/Diplomacy,Trade,Nations.json

@@ -184,7 +184,7 @@
 		Simplified_Chinese:"我们遇到了城邦--[name]！"		
 		Russian:"Мы обнаружили город-государство [name]!"
 	}
-	
+
 	// Friendship declaration flavor texts
 	"Declare Friendship ([numberOfTurns] turns)":{
 		Italian:"Dichiarazione di Amicizia ([numberOfTurns] turni)"

android/build.gradle

@@ -21,8 +21,8 @@ android {
         applicationId "com.unciv.app"
         minSdkVersion 14
         targetSdkVersion 29
-        versionCode 295
-        versionName "3.0.2"
+        versionCode 296
+        versionName "3.0.3"
     }
 
     // Had to add this crap for Travis to build, it wanted to sign the app

core/src/com/unciv/logic/civilization/CivilizationInfo.kt

@@ -12,6 +12,7 @@ import com.unciv.logic.civilization.diplomacy.DiplomacyManager
 import com.unciv.logic.civilization.diplomacy.DiplomaticStatus
 import com.unciv.logic.map.MapUnit
 import com.unciv.logic.map.TileInfo
+import com.unciv.logic.trade.TradeEvaluation
 import com.unciv.logic.trade.TradeRequest
 import com.unciv.models.gamebasics.*
 import com.unciv.models.gamebasics.tech.TechEra
@@ -56,6 +57,8 @@ class CivilizationInfo {
     var diplomacy = HashMap<String, DiplomacyManager>()
     var notifications = ArrayList<Notification>()
     val popupAlerts = ArrayList<PopupAlert>()
+
+    //** for trades here, ourOffers is the current civ's offers, and theirOffers is what the requesting civ offers  */
     val tradeRequests = ArrayList<TradeRequest>()
 
     // if we only use lists, and change the list each time the cities are changed,
@@ -332,6 +335,14 @@ class CivilizationInfo {
         for (city in cities) city.startTurn()
 
         getCivUnits().toList().forEach { it.startTurn() }
+
+        for(tradeRequest in tradeRequests.toList()) { // remove trade requests where one of the sides can no longer supply
+            val offeringCiv = gameInfo.getCivilization(tradeRequest.requestingCiv)
+            if (offeringCiv.isDefeated() || !TradeEvaluation().isTradeValid(tradeRequest.trade,this, offeringCiv)) {
+                tradeRequests.remove(tradeRequest)
+                offeringCiv.addNotification("Our proposed trade is no longer relevant!", Color.GOLD)
+            }
+        }
     }
 
     fun endTurn() {

core/src/com/unciv/logic/trade/TradeEvaluation.kt

@@ -11,6 +11,38 @@ import kotlin.math.min
 import kotlin.math.sqrt
 
 class TradeEvaluation{
+
+    fun isTradeValid(trade:Trade, offerer:CivilizationInfo, tradePartner: CivilizationInfo): Boolean {
+        for(offer in trade.ourOffers)
+            if(!isOfferValid(offer,offerer))
+                return false
+        for(offer in trade.theirOffers)
+            if(!isOfferValid(offer,tradePartner))
+                return false
+        return true
+    }
+
+    private fun isOfferValid(tradeOffer: TradeOffer, offerer:CivilizationInfo): Boolean {
+
+        fun hasResource(tradeOffer: TradeOffer): Boolean {
+            val resourcesByName = offerer.getCivResourcesByName()
+            return resourcesByName.containsKey(tradeOffer.name) && resourcesByName[tradeOffer.name]!! >= tradeOffer.amount
+        }
+
+        when(tradeOffer.type){
+            TradeType.Gold -> return true // even if they go negative it's okay
+            TradeType.Gold_Per_Turn -> return true // even if they go negative it's okay
+            TradeType.Treaty -> return true
+            TradeType.Agreement -> return true
+            TradeType.Luxury_Resource -> return hasResource(tradeOffer)
+            TradeType.Strategic_Resource -> return hasResource(tradeOffer)
+            TradeType.Technology -> return true
+            TradeType.Introduction -> return true
+            TradeType.WarDeclaration -> return true
+            TradeType.City -> return offerer.cities.any { it.name==tradeOffer.name }
+        }
+    }
+
     fun isTradeAcceptable(trade: Trade, evaluator: CivilizationInfo, tradePartner: CivilizationInfo): Boolean {
         var sumOfTheirOffers = trade.theirOffers.asSequence()
                 .filter { it.type!= TradeType.Treaty } // since treaties should only be evaluated once for 2 sides