/**
 * A LeadedPencil has a default length: When the constructor is called with a
 * non-positive length, the LeadedPencil is initialized to have the default
 * length.
 * 
 * @convention length > 0
 * @correspondence s = length <br /> c = color
 */
public class LeadedPencil implements Pencil {

	/**
	 * Default value used to initialize length if constructor is not called with
	 * a positive value.
	 */
	private static final int DEFAULT_LENGTH = 10;

	/**
	 * Color of the lead in this pencil. The lead can always be replaced with
	 * different color.
	 */
	private Colors color;

	/**
	 * The length of the pencil. This length is always positive.
	 */
	private int length;

	/**
	 * Initializes the LeadedPencil with the given length, unless the length is
	 * not positive, in which case the default length is used.
	 * 
	 * @param color
	 *            the initial lead color
	 * @param length
	 *            the initial length of the pencil
	 */
	public LeadedPencil(Colors color, int length) {
		this.color = color;
		this.length = DEFAULT_LENGTH;
		if (length > 0) {
			this.length = length;
		}
	}

	/**
	 * Returns a human-readable representation of the Pencil.
	 */
	public String toString() {
		return (this.length + ": " + this.color);
	}

	/**
	 * @param newColor
	 *            is a valid color
	 */
	public void setColor(Colors newColor) {
		this.color = newColor;
	}

	/**
	 * @param remove
	 *            amount by which pencil will be shortened
	 */
	public void sharpen(int remove) {
		assert (remove >= 0);
		if (remove < this.length) {
			this.length -= remove;
		}
	}
}