1 files changed, 197 insertions, 0 deletions
diff --git a/BJC-Utils2/src/main/java/bjc/utils/esodata/DoubleTape.java b/BJC-Utils2/src/main/java/bjc/utils/esodata/DoubleTape.java
new file mode 100644
index 0000000..410acf6
--- /dev/null
+++ b/BJC-Utils2/src/main/java/bjc/utils/esodata/DoubleTape.java
@@ -0,0 +1,197 @@
+package bjc.utils.esodata;
+
+import java.util.ArrayList;
+
+/**
+ * Double-sided tape is essentially two tapes stuck together with a shared cursor. 
+ *
+ * The main way a double-sided tape differs is that it can be flipped, allowing access to
+ * another set of data.
+ *
+ * However, there is only one cursor, and the position of the cursor on one side is the inverse
+ * of the position on the other side.
+ *
+ * When one side is extended, a null will be inserted into the inactive side regardless of the
+ * auto-extension policy of the tape. The policy will still be respected for the active side.
+ *
+ * All operations that refer to the tape refer to the currently active side of the tape, except for flip.
+ * 
+ * Flip refers to the entire tape for 'obvious' reasons.
+ *
+ * @param T The element type of the tape.
+ * @author bjculkin
+ */
+public class DoubleTape<T> implements Tape<T> {
+	private Tape<T> front;
+	private Tape<T> back;
+
+	/**
+	 * Create a new empty double-sided tape that doesn't autoextend.
+	 */
+	public DoubleTape() {
+		this(false);
+	}
+
+	/**
+	 * Create a new empty double-sided tape that follows the specified auto-extension policy.
+	 *
+	 * @param autoExtnd Whether or not to auto-extend the tape to the right
+	 * 			w/ nulls.
+	 */
+	public DoubleTape(boolean autoExtnd) {
+		front = new SingleTape<>(autoExtnd);
+		back  = new SingleTape<>(autoExtnd);
+	}
+
+	/**
+	 * Get the item the tape is currently on.
+	 *
+	 * @return The item the tape is on.
+	 */
+	public T item() {
+		return front.item();
+	}
+
+	/**
+	 * Set the item the tape is currently on.
+	 *
+	 * @param itm The new value for the tape item.
+	 */
+	public void item(T itm) {
+		front.item(itm);
+	}
+
+	/**
+	 * Get the current number of elements in the tape.
+	 *
+	 * @return The current number of elements in the tape.
+	 */
+	public int size() {
+		return front.size();
+	}
+
+	/**
+	 * Insert an element before the current item.
+	 *
+	 * @param itm The item to add.
+	 */
+	public void insertBefore(T itm) {
+		front.insertBefore(itm);
+		back.insertAfter(null);
+	}
+
+	/**
+	 * Insert an element after the current item.
+	 */
+	public void insertAfter(T itm) {
+		front.insertAfter(itm);
+		back.insertBefore(itm);
+	}
+
+	/**
+	 * Remove the current element.
+	 * 
+	 * Also moves the cursor back one step if possible to maintain
+	 * relative position, and removes the corresponding item from the non-active side
+	 *
+	 * @return The removed item from the active side.
+	 */
+	public T remove() {
+		back.remove();
+
+		return front.remove();
+	}
+
+	/**
+	 * Move the cursor to the left-most position.
+	 */
+	public void first() {
+		front.first();
+		back.last();
+	}
+
+	/**
+	 * Move the cursor the right-most position.
+	 */
+	public void last() {
+		front.last();
+		back.first();
+	}
+
+	/**
+	 * Move the cursor one space left.
+	 *
+	 * The cursor can't go past zero.
+	 *
+	 * @return True if the cursor was moved left.
+	 */
+	public boolean left() {
+		return left(1);
+	}
+
+	/**
+	 * Move the cursor the specified amount left.
+	 *
+	 * The cursor can't go past zero.
+	 * Attempts to move the cursor by amounts that would exceed zero
+	 * don't move the cursor at all.
+	 *
+	 * @param amt The amount to attempt to move the cursor left.
+	 *
+	 * @return True if the cursor was moved left.
+	 */
+	public boolean left(int amt) {
+		boolean succ = front.left(amt);
+
+		if(succ) back.right(amt);
+
+		return succ;
+	}
+
+
+	/**
+	 * Move the cursor one space right.
+	 *
+	 * Moving the cursor right will auto-extend the tape if that is enabled.
+	 *
+	 * @return Whether the cursor was moved right.
+	 */
+	public boolean right() {
+		return right(1);
+	}
+
+	/**
+	 * Move the cursor the specified amount right.
+	 *
+	 * Moving the cursor right will auto-extend the tape if that is enabled.
+	 *
+	 * @param amt The amount to move the cursor right by.
+	 *
+	 * @return Whether the cursor was moved right.
+	 */
+	public boolean right(int amt) {
+		boolean succ = front.right(amt);
+
+		if(succ) back.left(amt);
+
+		return succ;
+	}
+
+	/**
+	 * Flips the tape.
+	 *
+	 * The active side becomes inactive, and the inactive side becomes active.
+	 */
+	public void flip() {
+		Tape<T> tmp = front;
+
+		front = back;
+
+		back = tmp;
+	}
+
+	@Override
+	public boolean isDoubleSided() {
+		return true;
+	}
+}