package bjc.esodata;

/**
 * Interface for something that acts like a tape.
 *
 * A tape is essentially a 1D array with a cursor attached to it, and you can
 * only affect elements at that cursor. The size of the array is theoretically
 * unbounded to the right, but in practice bounded by available memory.
 *
 * @param <T>
 *                The element type of the tape.
 *
 * @author bjculkin
 */
public interface Tape<T> {
	/**
	 * Get the item the tape is currently on.
	 *
	 * @return The item the tape is on.
	 */
	T item();

	/**
	 * Set the item the tape is currently on.
	 *
	 * @param itm
	 *                The new value for the tape item.
	 */
	void item(T itm);

	/**
	 * Get the current number of elements in the tape.
	 *
	 * @return The current number of elements in the tape.
	 */
	int size();

	/**
	 * Get the position of the current item.
	 *
	 * @return The position of the current item.
	 */
	int position();

	/**
	 * Insert an element before the current item.
	 *
	 * @param itm
	 *                The item to add.
	 */
	void insertBefore(T itm);

	/**
	 * Insert an element after the current item.
	 *
	 * @param itm
	 *                The item to insert.
	 */
	void insertAfter(T itm);

	/**
	 * Remove the current element.
	 *
	 * Also moves the cursor back one step if possible to maintain relative
	 * position.
	 *
	 * @return The removed item.
	 */
	T remove();

	/** Move the cursor to the left-most position. */
	void first();

	/** Move the cursor to the right-most position. */
	void last();

	/**
	 * Move the cursor one space left.
	 *
	 * The cursor can't go past zero.
	 *
	 * @return True if the cursor was moved left.
	 */
	boolean left();

	/**
	 * 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.
	 */
	boolean left(int amt);

	/**
	 * Move the cursor one space right.
	 *
	 * @return Whether the cursor was moved right.
	 */
	boolean right();

	/**
	 * Move the cursor the specified amount right.
	 *
	 * @param amt
	 *                The amount to move the cursor right by.
	 *
	 * @return Whether the cursor was moved right.
	 */
	boolean right(int amt);

	/**
	 * Seek to an absolute position on the tape.
	 * 
	 * @param pos
	 *                The position to seek to.
	 * @return Whether or not the tape successfully seeked to that position.
	 */
	boolean seekTo(int pos);

	/**
	 * Check if this tape is at its end.
	 * 
	 * Equivalent to checking if position() == size().
	 * 
	 * @return Whether or not the tape is at its end.
	 */
	default boolean atEnd() {
		return position() == size();
	}
}