Add API to get transformed block (#28)

src/main/java/com/gtnewhorizons/postea/api/BlockNameAndMeta.java

@@ -0,0 +1,22 @@
+package com.gtnewhorizons.postea.api;
+
+/**
+ * A block referenced by its namespaced id, together with a meta value. Returned by
+ * {@link BlockReplacementManager#transformBlock(String, int)}.
+ */
+public final class BlockNameAndMeta {
+
+    /**
+     * The namespaced id of the block.
+     */
+    public final String name;
+    /**
+     * The meta value of the block.
+     */
+    public final int metadata;
+
+    public BlockNameAndMeta(String name, int metadata) {
+        this.name = name;
+        this.metadata = metadata;
+    }
+}

src/main/java/com/gtnewhorizons/postea/api/BlockReplacementManager.java

@@ -3,6 +3,7 @@ package com.gtnewhorizons.postea.api;
 import java.util.function.Consumer;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import net.minecraft.block.Block;
 import net.minecraftforge.oredict.OreDictionary;
@@ -54,6 +55,32 @@ public abstract class BlockReplacementManager {
 
     // endregion custom transformer registration
 
+    // region lookup
+
+    /**
+     * Runs the block transformers registered for the given id on a block that isn't placed in the world, and returns
+     * what it would be transformed into.<br>
+     * <br>
+     * This is meant for mods that store blocks by their namespaced id inside their own NBT (e.g.: blocks that are
+     * made out of other blocks), which Postea can't reach while converting chunks. Calling this when such a block is
+     * loaded applies every migration registered to Postea to it.
+     *
+     * @apiNote Only call this while a world is loaded, transformers rely on the numeric ids resolved for that world.
+     *          The transformers are given a {@link com.gtnewhorizons.postea.utility.BlockConversionInfo} without a
+     *          world, and with all coordinates set to 0. Tile entity transformers are not run.
+     *
+     * @param name     The namespaced id of the block.
+     * @param metadata The meta value of the block.
+     * @return The namespaced id and meta value of the block to use instead, or null if no transformer applies.
+     */
+    @SuppressWarnings("unused")
+    public static @Nullable BlockNameAndMeta transformBlock(@Nonnull String name, int metadata) {
+        if (name == null) throw new NullPointerException("name cannot be null");
+        return TransformerRegistry.transformBlock(name, metadata);
+    }
+
+    // endregion lookup
+
     // region id resolving
 
     // spotless:off

src/main/java/com/gtnewhorizons/postea/utility/TransformerRegistry.java

@@ -6,6 +6,7 @@ import java.util.List;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
+import net.minecraft.block.Block;
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.world.World;
 import net.minecraft.world.chunk.Chunk;
@@ -13,6 +14,7 @@ import net.minecraft.world.chunk.Chunk;
 import org.apache.commons.lang3.tuple.Pair;
 
 import com.google.common.collect.LinkedListMultimap;
+import com.gtnewhorizons.postea.api.BlockNameAndMeta;
 import com.gtnewhorizons.postea.api.IBlockTransformationHandler;
 import com.gtnewhorizons.postea.api.IDExtenderCompat;
 import com.gtnewhorizons.postea.api.IItemStackTransformationHandler;
@@ -20,6 +22,7 @@ import com.gtnewhorizons.postea.api.TriFunction;
 
 import cpw.mods.fml.common.Loader;
 import cpw.mods.fml.common.LoaderState;
+import cpw.mods.fml.common.registry.GameData;
 import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
 
 /**
@@ -156,6 +159,32 @@ public class TransformerRegistry {
         return null;
     }
 
+    public static @Nullable BlockNameAndMeta transformBlock(@Nonnull String name, int metadata) {
+        List<IBlockTransformationHandler> handlers = BLOCK_REPLACEMENT_MAP.get(name);
+        if (handlers.isEmpty()) return null;
+        // there is no position nor world, the block isn't placed anywhere
+        BlockConversionInfo blockConversionInfo = new BlockConversionInfo(
+            name,
+            IDRegistry.getBlockId(name),
+            metadata,
+            0,
+            0,
+            0,
+            null);
+        for (IBlockTransformationHandler transformer : handlers) {
+            if (transformer.apply(blockConversionInfo)) {
+                Block block = GameData.getBlockRegistry()
+                    .getRaw(blockConversionInfo.blockID);
+                if (block == null) return null;
+                return new BlockNameAndMeta(
+                    GameData.getBlockRegistry()
+                        .getNameForObject(block),
+                    blockConversionInfo.metadata);
+            }
+        }
+        return null;
+    }
+
     public static void transformItem(NBTTagCompound tag) {
         // abort early if tag is bad.
         if (tag.hasNoTags() || !tag.hasKey("id")) return;