Add some helpful transform methods

Fixes #12

tree/src/main/java/org/enginehub/linbus/tree/LinCompoundTag.java

@@ -34,6 +34,7 @@
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.function.Function;
 
 /**
  * Represents a compound tag.
@@ -395,6 +396,54 @@ public <T extends LinTag<?>> LinListTag<T> getListTag(
         return cast;
     }
 
+    private LinCompoundTag withChangedTag(String name, LinTag<?> value) {
+        LinkedHashMap<String, LinTag<?>> newMap = new LinkedHashMap<>(this.value);
+        newMap.put(name, value);
+        return new LinCompoundTag(Collections.unmodifiableMap(newMap), false);
+    }
+
+    /**
+     * Transform a value in the compound tag. You may change the type of the tag.
+     *
+     * <p>
+     * This uses {@link #getTag(String, LinTagType)}, so it will throw an exception if the tag does not exist
+     * or is of the wrong type.
+     * </p>
+     *
+     * @param name the name of the tag to transform
+     * @param type the type of the tag to transform
+     * @param transformer the function to transform the tag
+     * @return the new compound tag
+     */
+    public <T extends LinTag<?>> LinCompoundTag transformTag(
+        String name, LinTagType<T> type, Function<T, ? extends LinTag<?>> transformer
+    ) {
+        T tag = getTag(name, type);
+        LinTag<?> transformed = transformer.apply(tag);
+        return withChangedTag(name, transformed);
+    }
+
+    /**
+     * Transform a list value in the compound tag. You may change the type of the tag.
+     *
+     * <p>
+     * This uses {@link #getListTag(String, LinTagType)}, so it will throw an exception if the tag does not exist
+     * or is of the wrong type.
+     * </p>
+     *
+     * @param name the name of the tag to transform
+     * @param elementType the element type of the list tag to transform
+     * @param transformer the function to transform the tag
+     * @return the new compound tag
+     */
+    public <T extends LinTag<?>> LinCompoundTag transformListTag(
+        String name, LinTagType<T> elementType, Function<LinListTag<T>, ? extends LinTag<?>> transformer
+    ) {
+        LinListTag<T> tag = getListTag(name, elementType);
+        LinTag<?> transform = transformer.apply(tag);
+        return withChangedTag(name, transform);
+    }
+
     /**
      * Converts this tag into a {@link Builder}.
      *

tree/src/main/java/org/enginehub/linbus/tree/LinListTag.java

@@ -27,6 +27,7 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
+import java.util.function.Function;
 
 /**
  * Represents a list of {@link LinTag LinTags}.
@@ -219,6 +220,19 @@ public T get(int index) {
         return value.get(index);
     }
 
+    /**
+     * Transform the tag at the given index.
+     *
+     * @param index the index of the tag to transform
+     * @param transformer the function to transform the tag
+     * @return the new list tag
+     */
+    public LinListTag<T> transformTag(int index, Function<T, T> transformer) {
+        var newValue = new ArrayList<>(value);
+        newValue.set(index, transformer.apply(value.get(index)));
+        return new LinListTag<>(elementType, List.copyOf(newValue));
+    }
+
     /**
      * Converts this tag into a {@link Builder}.
      *

tree/src/main/java/org/enginehub/linbus/tree/LinRootEntry.java

@@ -32,6 +32,7 @@
 import java.io.UncheckedIOException;
 import java.util.Map;
 import java.util.Objects;
+import java.util.function.Function;
 
 /**
  * Represents the root implicit-compound-tag entry.
@@ -65,6 +66,26 @@ public static LinRootEntry readFrom(LinStream tokens) throws IOException {
         Objects.requireNonNull(value);
     }
 
+    /**
+     * Transform the name of this entry.
+     *
+     * @param nameTransformer the function to transform the name
+     * @return the new entry
+     */
+    public LinRootEntry transformName(Function<String, String> nameTransformer) {
+        return new LinRootEntry(nameTransformer.apply(name), value);
+    }
+
+    /**
+     * Transform the value of this entry.
+     *
+     * @param valueTransformer the function to transform the value
+     * @return the new entry
+     */
+    public LinRootEntry transformValue(Function<LinCompoundTag, LinCompoundTag> valueTransformer) {
+        return new LinRootEntry(name, valueTransformer.apply(value));
+    }
+
     /**
      * Write this entry to a byte array.
      *

tree/src/test/java/org/enginehub/linbus/tree/LinCompoundTagTest.java

@@ -137,6 +137,25 @@ void getByName() {
         }
     }
 
+    @Test
+    void transformByName() {
+        var tag = LinCompoundTag.of(new LinkedHashMap<>() {{
+            put("Hello", LinStringTag.of("World!"));
+            put("Goodbye", LinIntArrayTag.of(0xCAFE, 0xBABE));
+        }});
+        var transformed = tag.transformTag("Hello", LinTagType.stringTag(), t -> LinStringTag.of("New World!"));
+        assertThat(transformed).isEqualTo(LinCompoundTag.of(new LinkedHashMap<>() {{
+            put("Hello", LinStringTag.of("New World!"));
+            put("Goodbye", LinIntArrayTag.of(0xCAFE, 0xBABE));
+        }}));
+
+        var transformedToNewType = tag.transformTag("Hello", LinTagType.stringTag(), t -> LinIntArrayTag.of(0xDEAD, 0xBEEF));
+        assertThat(transformedToNewType).isEqualTo(LinCompoundTag.of(new LinkedHashMap<>() {{
+            put("Hello", LinIntArrayTag.of(0xDEAD, 0xBEEF));
+            put("Goodbye", LinIntArrayTag.of(0xCAFE, 0xBABE));
+        }}));
+    }
+
     @Test
     void findByName() {
         var tag = LinCompoundTag.of(new LinkedHashMap<>() {{

tree/src/test/java/org/enginehub/linbus/tree/LinListTagTest.java

@@ -64,6 +64,20 @@ void setOnBuilder() {
         ).isEqualTo(initial.toBuilder().set(0, LinStringTag.of("Goodbye...")).build());
     }
 
+    @Test
+    void transformByIndex() {
+        var initial = LinListTag.of(LinTagType.stringTag(), List.of(
+            LinStringTag.of("Hello"),
+            LinStringTag.of("World!")
+        ));
+        assertThat(
+            LinListTag.of(LinTagType.stringTag(), List.of(
+                LinStringTag.of("Hello"),
+                LinStringTag.of("Goodbye...")
+            ))
+        ).isEqualTo(initial.transformTag(1, s -> LinStringTag.of("Goodbye...")));
+    }
+
     @Test
     void emptyImplementation() {
         var empty = LinListTag.empty(LinTagType.stringTag());

tree/src/test/java/org/enginehub/linbus/tree/NestedTransformShowcaseTest.java

@@ -0,0 +1,29 @@
+package org.enginehub.linbus.tree;
+
+import org.junit.jupiter.api.Test;
+
+public class NestedTransformShowcaseTest {
+    @Test
+    void transformSchematicMetadata() {
+        LinRootEntry root = new LinRootEntry(
+            "",
+            LinCompoundTag.builder()
+                .put("Schematic", LinCompoundTag.builder()
+                    .put("Metadata", LinCompoundTag.builder()
+                        .put("Name", LinStringTag.of("My Schematic"))
+                        .put("Author", LinStringTag.of("Linbus"))
+                        .build())
+                    .build())
+                .build()
+        );
+        LinRootEntry withNewName = root.transformValue(v ->
+            v.transformTag("Schematic", LinTagType.compoundTag(), schematic ->
+                schematic.transformTag("Metadata", LinTagType.compoundTag(), metadata ->
+                    metadata.transformTag("Name", LinTagType.stringTag(), name ->
+                        LinStringTag.of("My New Schematic")
+                    )
+                )
+            )
+        );
+    }
+}