Added a new preliminary mapping + metadata framework.

The eventual goal is to add:

1. Support for mapping block, etc. names (minecraft:stone, etc.)
2. Proper support for entities in WorldEdit
3. Support for querying for metadata about a block, entity, etc.
4. Extent support to biomes, structures, and so on

src/main/java/com/sk89q/worldedit/world/NullWorld.java

@@ -23,8 +23,14 @@ import com.sk89q.worldedit.*;
 import com.sk89q.worldedit.blocks.BaseBlock;
 import com.sk89q.worldedit.blocks.BaseItemStack;
 import com.sk89q.worldedit.blocks.BlockID;
+import com.sk89q.worldedit.entity.BaseEntity;
+import com.sk89q.worldedit.entity.Entity;
 import com.sk89q.worldedit.regions.Region;
 import com.sk89q.worldedit.util.TreeGenerator.TreeType;
+import com.sk89q.worldedit.world.mapping.NullResolver;
+import com.sk89q.worldedit.world.mapping.Resolver;
+
+import javax.annotation.Nullable;
 
 /**
  * A null implementation of {@link World} that drops all changes and
@@ -95,4 +101,31 @@ public class NullWorld extends AbstractWorld {
         return new BaseBlock(BlockID.AIR);
     }
 
+    @Override
+    public Resolver<BaseBlock> getBlockMapping() {
+        return new NullResolver<BaseBlock>();
+    }
+
+    @Override
+    public Resolver<BaseEntity> getEntityMapping() {
+        return new NullResolver<BaseEntity>();
+    }
+
+    @Nullable
+    @Override
+    public <T> T getMetaData(BaseBlock block, Class<T> metaDataClass) {
+        return null;
+    }
+
+    @Nullable
+    @Override
+    public <T> T getMetaData(Entity entity, Class<T> metaDataClass) {
+        return null;
+    }
+
+    @Nullable
+    @Override
+    public <T> T getMetaData(BaseEntity entity, Class<T> metaDataClass) {
+        return null;
+    }
 }

src/main/java/com/sk89q/worldedit/world/World.java

@@ -27,11 +27,12 @@ import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.regions.Region;
 import com.sk89q.worldedit.util.TreeGenerator;
 import com.sk89q.worldedit.util.TreeGenerator.TreeType;
+import com.sk89q.worldedit.world.mapping.Mapping;
 
 /**
  * Represents a world (dimension).
  */
-public interface World extends Extent {
+public interface World extends Extent, Mapping {
 
     /**
      * Get the name of the world.

src/main/java/com/sk89q/worldedit/world/mapping/Mapping.java

@@ -0,0 +1,114 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.world.mapping;
+
+import com.sk89q.worldedit.blocks.BaseBlock;
+import com.sk89q.worldedit.entity.BaseEntity;
+import com.sk89q.worldedit.entity.Entity;
+import com.sk89q.worldedit.entity.metadata.Tameable;
+
+import javax.annotation.Nullable;
+
+/**
+ * A mapping can create state objects (such as {@link BaseBlock})
+ * from implementation-independent identifiers (such as "minecraft.stone"),
+ * as well as perform the opposite task of retrieving
+ * the identifier for a given state object (whenever possible at least, because
+ * a mapping may not be compatible with a set of state objects that may have
+ * come from another implementation). In addition, a mapping may be able to
+ * retrieve a variety of metadata objects (such as {@link Tameable}) to
+ * describe a given state object.
+ * </p>
+ * However, it may be possible that a mapping be "dumb" and not be able to,
+ * for example, return a {@link Tameable} for a "Horse" entity, simply because
+ * it has not be implemented. Any code that queries a mapping must be
+ * aware of this and act accordingly.
+ */
+public interface Mapping {
+
+    /**
+     * Get the mapping for block identifiers.
+     *
+     * @return a block mapping
+     */
+    Resolver<BaseBlock> getBlockMapping();
+
+    /**
+     * Get the mapping for entity identifiers.
+     *
+     * @return an entity mapping
+     */
+    Resolver<BaseEntity> getEntityMapping();
+
+    /**
+     * Attempt to return an instance of the given class for the given block.
+     * For example, {@code getMetaData(block, Inventory.class)} might return
+     * an instance if the block happens to contain an inventory.
+     * </p>
+     * If the given block is not of the given class (i.e. a dirt block does
+     * not have an inventory) or if the information is simply not available,
+     * {@code null} will be returned.
+     * </p>
+     * Mutator methods on the returned instance should change the block.
+     *
+     * @param block the block
+     * @param metaDataClass the metadata class for the returned instance
+     * @param <T> the metadata class
+     * @return an instance of the given class, otherwise null
+     */
+    @Nullable <T> T getMetaData(BaseBlock block, Class<T> metaDataClass);
+
+    /**
+     * Attempt to return an instance of the given class for the given entity.
+     * For example, {@code getMetaData(entity, Creature.class)} might return
+     * an instance if the entity happens to be a creature.
+     * </p>
+     * If the given entity is not of the given class (i.e. a painting is
+     * not a creature) or if the information is simply not available,
+     * {@code null} will be returned.
+     * </p>
+     * Mutator methods on the returned instance should change the entity.
+     *
+     * @param entity the entity
+     * @param metaDataClass the metadata class for the returned instance
+     * @param <T> the metadata class
+     * @return an instance of the given class, otherwise null
+     */
+    @Nullable <T> T getMetaData(Entity entity, Class<T> metaDataClass);
+
+    /**
+     * Attempt to return an instance of the given class for the given entity.
+     * For example, {@code getMetaData(entity, Creature.class)} might return
+     * an instance if the entity happens to be a creature.
+     * </p>
+     * If the given entity is not of the given class (i.e. a painting is
+     * not a creature) or if the information is simply not available,
+     * {@code null} will be returned.
+     * </p>
+     * Mutator methods on the returned instance should change the entity.
+     *
+     * @param entity the entity
+     * @param metaDataClass the metadata class for the returned instance
+     * @param <T> the metadata class
+     * @return an instance of the given class, otherwise null
+     */
+    @Nullable <T> T getMetaData(BaseEntity entity, Class<T> metaDataClass);
+
+}

src/main/java/com/sk89q/worldedit/world/mapping/NullResolver.java

@@ -0,0 +1,44 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.world.mapping;
+
+import javax.annotation.Nullable;
+
+/**
+ * An implementation of a {@link Resolver} that knows nothing and returns
+ * {@code null} in all cases.
+ *
+ * @param <E> the object to resolve
+ */
+public class NullResolver<E> implements Resolver<E> {
+
+    @Nullable
+    @Override
+    public E create(String id) {
+        return null;
+    }
+
+    @Nullable
+    @Override
+    public String getId(E object) {
+        return null;
+    }
+
+}

src/main/java/com/sk89q/worldedit/world/mapping/Resolver.java

@@ -0,0 +1,56 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.world.mapping;
+
+import com.sk89q.worldedit.blocks.BaseBlock;
+
+import javax.annotation.Nullable;
+
+/**
+ * A resolver can create state objects (such as {@link BaseBlock}) from
+ * universal identifiers, but also get the universal identifier for
+ * a given state object (at least when it is known).
+ * </p>
+ * Identifiers may be case-sensitive. Routines that work with IDs should
+ * not make changes to the casing of the IDs or perform case-insensitive
+ * comparisons. Implementations may normalize the casing of IDs if it
+ * is appropriate.
+ *
+ * @param <E> the type of state object
+ */
+public interface Resolver<E> {
+
+    /**
+     * Create an instance of the state object from the given ID.
+     *
+     * @param id the ID
+     * @return an instance, otherwise null if an instance cannot be created
+     */
+    @Nullable E create(String id);
+
+    /**
+     * Get the ID for the given object.
+     *
+     * @param object the object
+     * @return the ID, otherwise null if it is not known
+     */
+    @Nullable String getId(E object);
+
+}