From e6ff84b22248c3c66b7d3fd619132e48a89db5ef Mon Sep 17 00:00:00 2001
From: bculkin2442 <bjculkin@mix.wvu.edu>
Date: Mon, 29 Oct 2018 20:09:28 -0400
Subject: QueuedIterators

QueuedIterators are iterators that can have other iterators interleaved
into their iteration sequences. This was implemented as a decent idea,
and because it may help get the iterative topDownTransform working again
(if it ever worked in the first place...)
---
 .../main/java/bjc/utils/data/QueuedIterator.java   | 171 +++++++++++++++++++++
 1 file changed, 171 insertions(+)
 create mode 100644 base/src/main/java/bjc/utils/data/QueuedIterator.java

(limited to 'base/src/main')

diff --git a/base/src/main/java/bjc/utils/data/QueuedIterator.java b/base/src/main/java/bjc/utils/data/QueuedIterator.java
new file mode 100644
index 0000000..d75a9a3
--- /dev/null
+++ b/base/src/main/java/bjc/utils/data/QueuedIterator.java
@@ -0,0 +1,171 @@
+package bjc.utils.data;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.Iterator;
+
+/**
+ * An iterator that supports queuing elements after/before the current iterator;
+ * 
+ * @author bjculkin
+ *
+ * @param <E>
+ */
+public class QueuedIterator<E> implements Iterator<E> {
+	private Iterator<E> cur;
+
+	private Deque<Iterator<E>> pending;
+
+	/**
+	 * Static method for constructing iterators.
+	 * 
+	 * @return A queued iterator.
+	 */
+	public static <E> QueuedIterator<E> queued() {
+		return new QueuedIterator<>();
+	}
+
+	/**
+	 * Static method for constructing iterators.
+	 * 
+	 * @param itrs
+	 *                The iterators to use.
+	 * @return A queued iterator over the provided iterators.
+	 */
+	@SafeVarargs
+	public static <E> QueuedIterator<E> queued(Iterator<E>... itrs) {
+		return new QueuedIterator<>(itrs);
+	}
+
+	/**
+	 * Static method for constructing iterators.
+	 * 
+	 * @param itrs
+	 *                The iterables to use.
+	 * @return A queued iterator over the provided iterables.
+	 */
+	@SafeVarargs
+	public static <E> QueuedIterator<E> queued(Iterable<E>... itrs) {
+		return new QueuedIterator<>(itrs);
+	}
+
+	/**
+	 * Create a new queued iterator that starts blank.
+	 */
+	public QueuedIterator() {
+		pending = new ArrayDeque<>();
+	}
+
+	/**
+	 * Create a new queued iterator with a set of initial sources.
+	 * 
+	 * @param inits
+	 *                The set of initial iterators to use.
+	 */
+	@SafeVarargs
+	public QueuedIterator(Iterator<E>... inits) {
+		this();
+
+		for (Iterator<E> init : inits) {
+			pending.add(init);
+		}
+	}
+
+	/**
+	 * Create a new queued iterator with a set of initial sources.
+	 * 
+	 * @param inits
+	 *                The set of initial iterables to use.
+	 */
+	@SafeVarargs
+	public QueuedIterator(Iterable<E>... inits) {
+		this();
+
+		for (Iterable<E> init : inits) {
+			pending.add(init.iterator());
+		}
+	}
+
+	/**
+	 * Add a new iterator who we will iterate through first.
+	 * 
+	 * @param itr
+	 *                The iterator to go through first.
+	 */
+	public void before(Iterator<E> itr) {
+		pending.push(cur);
+
+		cur = itr;
+	}
+
+	/**
+	 * Add a new iterable who we will iterate through first.
+	 * 
+	 * @param itr
+	 *                The iterable to go through first.
+	 */
+	public void before(Iterable<E> itr) {
+		before(itr.iterator());
+	}
+	
+	/**
+	 * Add a new iterator who we will iterate through next.
+	 * 
+	 * @param itr
+	 *                The iterator to go through next.
+	 */
+	public void after(Iterator<E> itr) {
+		pending.push(itr);
+	}
+	/**
+	 * Add a new iterable who we will iterate through next.
+	 * 
+	 * @param itr
+	 *                The iterable to go through next.
+	 */
+	public void after(Iterable<E> itr) {
+		after(itr.iterator());
+	}
+	
+	/**
+	 * Add a new iterator who we will iterate through last.
+	 * 
+	 * @param itr
+	 *                The iterator to go through last.
+	 */
+	public void last(Iterator<E> itr) {
+		pending.add(itr);
+	}
+
+	/**
+	 * Add a new iterable who we will iterate through last.
+	 * 
+	 * @param itr
+	 *                The iterable to go through last.
+	 */
+	public void last(Iterable<E> itr) {
+		last(itr.iterator());
+	}
+	@Override
+	public boolean hasNext() {
+		while (cur == null || !cur.hasNext()) {
+			if (pending.isEmpty()) return false;
+
+			cur = pending.pop();
+		}
+
+		return cur.hasNext();
+	}
+
+	@Override
+	public E next() {
+		while (cur == null || !cur.hasNext()) {
+			if (pending.isEmpty()) return null;
+
+			cur = pending.pop();
+		}
+
+		return cur.next();
+	}
+
+}
-- 
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