G2-1509 Support DFS with parent reporting

ax-java/src/main/java/com/g2forge/alexandria/java/core/helpers/HTree.java

@@ -6,6 +6,8 @@
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
+import com.g2forge.alexandria.java.adt.tuple.ITuple2G_;
+import com.g2forge.alexandria.java.adt.tuple.implementations.Tuple2G_I;
 import com.g2forge.alexandria.java.core.marker.Helpers;
 
 import lombok.experimental.UtilityClass;
@@ -19,6 +21,12 @@ public static <N> Stream<N> dfs(N node, final Function<? super N, ? extends Coll
 		else return children.stream().map(child -> dfs(child, getChildren, postorder)).reduce(Stream.of(node), postorder ? (s0, s1) -> Stream.concat(s1, s0) : Stream::concat);
 	}
 
+	public static <N> Stream<ITuple2G_<N, N>> dfsWithParent(N parent, N node, final Function<? super N, ? extends Collection<? extends N>> getChildren, boolean postorder) {
+		final Collection<? extends N> children = getChildren.apply(node);
+		if ((children == null) || children.isEmpty()) return Stream.of(new Tuple2G_I<>(parent, node));
+		else return children.stream().map(child -> dfsWithParent(node, child, getChildren, postorder)).reduce(Stream.of(new Tuple2G_I<>(parent, node)), postorder ? (s0, s1) -> Stream.concat(s1, s0) : Stream::concat);
+	}
+
 	public static <N> Optional<N> find(N node, final Function<? super N, ? extends Collection<? extends N>> getChildren, Predicate<? super N> find) {
 		if (find.test(node)) return Optional.of(node);
 		for (N child : getChildren.apply(node)) {

ax-java/src/test/java/com/g2forge/alexandria/java/core/helpers/TestHTree.java

@@ -0,0 +1,92 @@
+package com.g2forge.alexandria.java.core.helpers;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.g2forge.alexandria.java.adt.name.IStringNamed;
+import com.g2forge.alexandria.java.adt.tuple.ITuple2G_;
+import com.g2forge.alexandria.java.adt.tuple.implementations.Tuple2G_I;
+
+import lombok.Builder;
+import lombok.Data;
+import lombok.RequiredArgsConstructor;
+import lombok.Singular;
+
+public class TestHTree {
+	@Data
+	@Builder(toBuilder = true)
+	@RequiredArgsConstructor
+	protected static class Node implements IStringNamed {
+		public static NodeBuilder named(String name) {
+			return builder().name(name);
+		}
+
+		protected final String name;
+
+		@Singular
+		protected final List<Node> children;
+	}
+
+	protected void assertDFS(final Node root, final List<Node> expected, final boolean postorder) {
+		Assert.assertEquals(expected, HTree.dfs(root, Node::getChildren, postorder).collect(Collectors.toList()));
+	}
+
+	protected void assertDFSWithParent(final Node root, final List<ITuple2G_<Node, Node>> expected, final boolean postorder) {
+		Assert.assertEquals(expected, HTree.dfsWithParent(null, root, Node::getChildren, postorder).collect(Collectors.toList()));
+	}
+
+	@Test
+	public void dfsChild() {
+		final Node b, a = Node.named("a").child(b = Node.named("b").build()).build();
+		assertDFS(a, HCollection.asList(a, b), false);
+	}
+
+	@Test
+	public void dfsChildren() {
+		final Node c, b, a = Node.named("a").child(b = Node.named("b").build()).child(c = Node.named("c").build()).build();
+		assertDFS(a, HCollection.asList(a, b, c), false);
+		assertDFS(a, HCollection.asList(c, b, a), true);
+	}
+
+	@Test
+	public void dfsGrandchildren() {
+		final Node d, c, b, a = Node.named("a").child(b = Node.named("b").child(c = Node.named("c").build()).child(d = Node.named("d").build()).build()).build();
+		assertDFS(a, HCollection.asList(a, b, c, d), false);
+		assertDFS(a, HCollection.asList(d, c, b, a), true);
+	}
+
+	@Test
+	public void dfsSingle() {
+		final Node a = Node.named("a").build();
+		assertDFS(a, HCollection.asList(a), false);
+	}
+
+	@Test
+	public void dfsWithParentChild() {
+		final Node b, a = Node.named("a").child(b = Node.named("b").build()).build();
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(null, a), new Tuple2G_I<>(a, b)), false);
+	}
+
+	@Test
+	public void dfsWithParentChildren() {
+		final Node c, b, a = Node.named("a").child(b = Node.named("b").build()).child(c = Node.named("c").build()).build();
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(null, a), new Tuple2G_I<>(a, b), new Tuple2G_I<>(a, c)), false);
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(a, c), new Tuple2G_I<>(a, b), new Tuple2G_I<>(null, a)), true);
+	}
+
+	@Test
+	public void dfsWithParentGrandchild() {
+		final Node d, c, b, a = Node.named("a").child(b = Node.named("b").child(c = Node.named("c").build()).child(d = Node.named("d").build()).build()).build();
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(null, a), new Tuple2G_I<>(a, b), new Tuple2G_I<>(b, c), new Tuple2G_I<>(b, d)), false);
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(b, d), new Tuple2G_I<>(b, c), new Tuple2G_I<>(a, b), new Tuple2G_I<>(null, a)), true);
+	}
+
+	@Test
+	public void dfsWithParentSingle() {
+		final Node a = Node.named("a").build();
+		assertDFSWithParent(a, HCollection.asList(new Tuple2G_I<>(null, a)), false);
+	}
+}