Trees are now backed with a registry, custom trees can override Vanilla ones.

src/main/java/com/dfsek/terra/config/base/ConfigPack.java

@@ -1,5 +1,6 @@
 package com.dfsek.terra.config.base;
 
+import com.dfsek.terra.Debug;
 import com.dfsek.terra.Terra;
 import com.dfsek.terra.biome.UserDefinedBiome;
 import com.dfsek.terra.carving.UserDefinedCarver;
@@ -16,6 +17,7 @@ import com.dfsek.terra.config.genconfig.biome.AbstractBiomeConfig;
 import com.dfsek.terra.config.genconfig.biome.BiomeConfig;
 import com.dfsek.terra.config.genconfig.structure.StructureConfig;
 import com.dfsek.terra.config.lang.LangUtil;
+import com.dfsek.terra.tree.TreeRegistry;
 import com.dfsek.terra.util.StructureTypeEnum;
 import org.bukkit.configuration.ConfigurationSection;
 import org.bukkit.configuration.InvalidConfigurationException;
@@ -67,7 +69,7 @@ public class ConfigPack extends YamlConfiguration {
     private final Map<String, AbstractBiomeConfig> abstractBiomes;
     private final Map<String, BiomeConfig> biomes;
     private final Map<String, BiomeGridConfig> grids;
-    private final Map<String, TreeConfig> trees;
+    private final TreeRegistry treeRegistry = new TreeRegistry();
     private final Set<StructureConfig> allStructures = new HashSet<>();
     private final File dataFolder;
     private final String id;
@@ -90,7 +92,12 @@ public class ConfigPack extends YamlConfiguration {
 
         structures = ConfigLoader.load(new File(file, "structures").toPath(), this, StructureConfig.class);
 
-        trees = ConfigLoader.load(new File(file, "trees").toPath(), this, TreeConfig.class);
+        Map<String, TreeConfig> trees = ConfigLoader.load(new File(file, "trees").toPath(), this, TreeConfig.class);
+
+        for(Map.Entry<String, TreeConfig> entry : trees.entrySet()) {
+            if(treeRegistry.add(entry.getKey(), entry.getValue()))
+                Debug.info("Overriding Vanilla tree: " + entry.getKey());
+        }
 
         abstractBiomes = ConfigLoader.load(new File(file, "abstract" + File.separator + "biomes").toPath(), this, AbstractBiomeConfig.class);
 
@@ -278,7 +285,7 @@ public class ConfigPack extends YamlConfiguration {
         return flora.get(id);
     }
 
-    public TreeConfig getTree(String id) {
-        return trees.get(id);
+    public TreeRegistry getTreeRegistry() {
+        return treeRegistry;
     }
 }

src/main/java/com/dfsek/terra/config/genconfig/biome/BiomeTreeConfig.java

@@ -8,7 +8,6 @@ import org.bukkit.configuration.InvalidConfigurationException;
 import org.polydev.gaea.math.ProbabilityCollection;
 import org.polydev.gaea.math.Range;
 import org.polydev.gaea.tree.Tree;
-import org.polydev.gaea.tree.TreeType;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -32,13 +31,9 @@ public class BiomeTreeConfig extends TerraConfigSection {
                 Map<?, ?> y = ((ConfigurationSection) val.get("y")).getValues(false);
                 Tree tree;
                 try {
-                    tree = TreeType.valueOf(e.getKey());
-                } catch(IllegalArgumentException ex) {
-                    try {
-                        tree = Objects.requireNonNull(parent.getConfig().getTree(e.getKey()));
-                    } catch(NullPointerException ex2) {
-                        throw new ConfigException("Invalid tree type: \"" + e.getKey() + "\"", parent.getID());
-                    }
+                    tree = Objects.requireNonNull(parent.getConfig().getTreeRegistry().get(e.getKey()));
+                } catch(NullPointerException ex2) {
+                    throw new ConfigException("Invalid tree type: \"" + e.getKey() + "\"", parent.getID());
                 }
                 trees.add(tree, (Integer) val.get("weight"));
                 treeHeights.put(tree, new Range((Integer) y.get("min"), (Integer) y.get("max")));

src/main/java/com/dfsek/terra/tree/TreeRegistry.java

@@ -0,0 +1,36 @@
+package com.dfsek.terra.tree;
+
+import org.polydev.gaea.tree.Tree;
+import org.polydev.gaea.tree.TreeType;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class TreeRegistry {
+    private final Map<String, Tree> trees = new HashMap<>();
+
+    public TreeRegistry() {
+        for(TreeType t : TreeType.values()) trees.put(t.toString(), t); // Populate registry with default trees.
+    }
+
+    /**
+     * Add a tree to the registry with a name.
+     *
+     * @param name  Name of the tree.
+     * @param value Tree to add
+     * @return True if tree was overwritten.
+     */
+    public boolean add(String name, Tree value) {
+        boolean exists = trees.containsKey(name);
+        trees.put(name, value);
+        return exists;
+    }
+
+    public boolean contains(String name) {
+        return trees.containsKey(name);
+    }
+
+    public Tree get(String id) {
+        return trees.get(id);
+    }
+}