Improved Dungeon Loot and Selection

DDLoot: Implemented a custom version of MC's generateChestContents() for
our own chests. It avoids two notable bugs that affect MC's version.

FillContainersOperation: Changed code to use
DDLoot.generateChestContents()

SchematicLoader: Fixed a bug in the way we calculated a seed for
selecting our dungeons that would cause certain seeds to dominate all
the others. Under certain circumstances, the function would only return
-1. That would make our dungeon selection severely biased. That was
resolved and the code was specifically tuned for seeding Java's Random
even for doors with nearly identical positions. The result was an
apparent major improvement in the randomness of dungeons.

ruins\rules.txt: Changed the dungeon generation rules to precisely match
the complicated scheme we had before. We're still using simple rules to
choose dungeons - I used a program to derive the effective distribution
of dungeon types that the old code would produce and converted it into
the current rule system.

StevenDimDoors/mod_pocketDim/DDLoot.java

@@ -4,7 +4,10 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Random;
 
+import net.minecraft.inventory.IInventory;
 import net.minecraft.item.Item;
+import net.minecraft.item.ItemStack;
+import net.minecraft.util.WeightedRandom;
 import net.minecraft.util.WeightedRandomChestContent;
 import net.minecraftforge.common.ChestGenHooks;
 
@@ -33,6 +36,8 @@ public class DDLoot {
 	private static final int RARE_LOOT_WEIGHT = 1; //Same weight as music discs, golden apple
 	private static final int DUNGEON_CHEST_WEIGHT_INFLATION = 10; // (weight of iron ingots in dungeon) / (weight of iron ingots in other chests)
 	
+	private DDLoot() { }
+	
 	public static void registerInfo()
 	{
 		DDProperties properties = DDProperties.instance();
@@ -156,4 +161,48 @@ public class DDLoot {
 			//System.out.println(item.theItemId.getDisplayName() + "\t" + item.itemWeight);
 		}
 	}
+	
+	public static void generateChestContents(ChestGenHooks chestInfo, IInventory inventory, Random random)
+    {
+		//This is a custom version of net.minecraft.util.WeightedRandomChestContent.generateChestContents()
+		//It's designed to avoid the following bugs in MC 1.5:
+		//1. The randomized filling algorithm will sometimes overwrite item stacks with other stacks
+		//2. If multiple enchanted books appear, then they will have the same enchantment
+		
+		//The prime number below is used for choosing chest slots in a seemingly-random pattern. Its value
+		//was selected specifically to achieve a spread-out distribution for chests with up to 104 slots.
+		//Choosing a prime number ensures that our increments are relatively-prime to the chest size, which
+		//means we'll cover all the slots before repeating any. This is mathematically guaranteed.
+		final int primeOffset = 239333;
+		
+		int count = chestInfo.getCount(random);
+		int size = inventory.getSizeInventory();
+		WeightedRandomChestContent[] content = chestInfo.getItems(random);
+		
+        for (int k = 0; k < count; k++)
+        {
+            WeightedRandomChestContent selection = (WeightedRandomChestContent)WeightedRandom.getRandomItem(random, content);
+            
+            //Call getChestGenBase() to make sure we generate a different enchantment for books.
+            //Don't just use a condition to check if the item is an instance of ItemEnchantedBook because
+            //we don't know if other mods might add items that also need to be regenerated.
+            selection = selection.theItemId.getItem().getChestGenBase(chestInfo, random, selection);
+            
+            ItemStack[] stacks = ChestGenHooks.generateStacks(random, selection.theItemId, selection.theMinimumChanceToGenerateItem, selection.theMaximumChanceToGenerateItem);
+
+            for (ItemStack item : stacks)
+            {
+            	int limit = size;
+            	int index = random.nextInt(size);
+
+            	while (limit > 0 && inventory.getStackInSlot(index) != null)
+            	{
+            		limit--;
+            		index = (index + primeOffset) % size;
+            	}
+            	
+                inventory.setInventorySlotContents(index, item);
+            }
+        }
+    }
 }