1 files changed, 228 insertions, 0 deletions
diff --git a/src/main/java/bjc/data/QueuedIterator.java b/src/main/java/bjc/data/QueuedIterator.java
new file mode 100644
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+++ b/src/main/java/bjc/data/QueuedIterator.java
@@ -0,0 +1,228 @@
+package bjc.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 vals
+	 * 		The values to iterate over.
+	 *
+	 * @return A queued iterator.
+	 */
+	public static <E> QueuedIterator<E> queued(E... vals) {
+		return new QueuedIterator<>(new ArrayIterator<>(vals));
+	}
+
+	/**
+	 * 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());
+		}
+	}
+
+	/**
+	 * Create a new queued iterator with a set of initial values.
+	 * 
+	 * @param vals
+	 * 		The set of initial values to use.
+	 */
+	@SafeVarargs
+	public QueuedIterator(E... vals) {
+		this(new ArrayIterator(vals));
+	}
+
+	/**
+	 * 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 set of values who we will iterate through first.
+	 * 
+	 * @param vals
+	 * 		Values to iterate over first.
+	 */
+	public void before(E... vals) {
+		before(new ArrayIterator<>(vals));
+	}
+
+	/**
+	 * 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 set of values who we will iterate through next.
+	 * 
+	 * @param vals
+	 * 		The values to iterate over next.
+	 */
+	public void after(E... vals) {
+		after(new ArrayIterator<>(vals));
+	}
+	
+	/**
+	 * 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());
+	}
+
+	/**
+	 * Add a new set of values who we will iterate through last.
+	 * 
+	 * @param itr
+	 *                The iterable to go through last.
+	 */
+	public void last(E... vals) {
+		last(new ArrayIterator<>(vals));
+	}
+
+	@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();
+	}
+
+}