Configurable minimum demand for trades

Addresses MC-163962 where villager demand decreases indefinitely. Paper adds a patch to fix this by preventing demand from going below zero. This patch adds a config option to allow the minimum demand to instead be configurable.

purpur-server/minecraft-patches/sources/net/minecraft/world/entity/npc/Villager.java.patch

@@ -22,6 +22,15 @@
                  this.startTrading(player);
              }
  
+@@ -503,7 +_,7 @@
+ 
+     private void updateDemand() {
+         for (MerchantOffer merchantOffer : this.getOffers()) {
+-            merchantOffer.updateDemand();
++            merchantOffer.updateDemand(this.level().purpurConfig.villagerMinimumDemand); // Purpur - Configurable minimum demand for trades
+         }
+     }
+ 
 @@ -707,7 +_,7 @@
  
      @Override

purpur-server/minecraft-patches/sources/net/minecraft/world/item/trading/MerchantOffer.java.patch

@@ -0,0 +1,16 @@
+--- a/net/minecraft/world/item/trading/MerchantOffer.java
++++ b/net/minecraft/world/item/trading/MerchantOffer.java
+@@ -143,7 +_,12 @@
+     }
+ 
+     public void updateDemand() {
+-        this.demand = Math.max(0, this.demand + this.uses - (this.maxUses - this.uses)); // Paper - Fix MC-163962
++        // Purpur start - Configurable minimum demand for trades
++        this.updateDemand(0);
++    }
++    public void updateDemand(int minimumDemand) {
++        this.demand = Math.max(minimumDemand, this.demand + this.uses - (this.maxUses - this.uses)); // Paper - Fix MC-163962
++        // Purpur end - Configurable minimum demand for trades
+     }
+ 
+     public ItemStack assemble() {

purpur-server/src/main/java/org/purpurmc/purpur/PurpurWorldConfig.java

@@ -2913,6 +2913,7 @@ public class PurpurWorldConfig {
     public boolean villagerTakeDamageFromWater = false;
     public boolean villagerAllowTrading = true;
     public boolean villagerAlwaysDropExp = false;
+    public int villagerMinimumDemand = 0;
     private void villagerSettings() {
         villagerRidable = getBoolean("mobs.villager.ridable", villagerRidable);
         villagerRidableInWater = getBoolean("mobs.villager.ridable-in-water", villagerRidableInWater);
@@ -2935,6 +2936,7 @@ public class PurpurWorldConfig {
         villagerTakeDamageFromWater = getBoolean("mobs.villager.takes-damage-from-water", villagerTakeDamageFromWater);
         villagerAllowTrading = getBoolean("mobs.villager.allow-trading", villagerAllowTrading);
         villagerAlwaysDropExp = getBoolean("mobs.villager.always-drop-exp", villagerAlwaysDropExp);
+        villagerMinimumDemand = getInt("mobs.villager.minimum-demand", villagerMinimumDemand);
     }
 
     public boolean vindicatorRidable = false;