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package org.scijava;

/**
 * Constants for specifying an item's priority.
 * 
 * @author Johannes Schindelin
 * @author Curtis Rueden
 * @see org.scijava.Prioritized#getPriority()
 * @see org.scijava.plugin.Plugin#priority()
 */
public final class Priority {

	private Priority() {
		// prevent instantiation of utility class
	}

	/** Priority for items that must be sorted first. */
	public static final double FIRST_PRIORITY = Double.POSITIVE_INFINITY;

	/** Priority for items that strongly prefer to be sorted early. */
	public static final double VERY_HIGH_PRIORITY = +10000;

	/** Priority for items that prefer to be sorted earlier. */
	public static final double HIGH_PRIORITY = +100;

	/** Default priority for items. */
	public static final double NORMAL_PRIORITY = 0;

	/** Priority for items that prefer to be sorted later. */
	public static final double LOW_PRIORITY = -100;

	/** Priority for items that strongly prefer to be sorted late. */
	public static final double VERY_LOW_PRIORITY = -10000;

	/** Priority for items that must be sorted last. */
	public static final double LAST_PRIORITY = Double.NEGATIVE_INFINITY;

	/**
	 * Compares two {@link Prioritized} objects.
	 * <p>
	 * Note: this method provides a natural ordering that may be inconsistent with
	 * equals. That is, two unequal objects may often have the same priority, and
	 * thus return 0 when compared in this fashion. Hence, if this method is used
	 * as a basis for implementing {@link Comparable#compareTo} or
	 * {@link java.util.Comparator#compare}, that implementation may want to
	 * impose logic beyond that of this method, for breaking ties, if a total
	 * ordering consistent with equals is always required.
	 * </p>
	 * 
	 * @return -1 if {@code p1}'s priority is higher than {@code p2}'s, 1 if
	 *         {@code p2}'s priority is higher than {@code p1}'s, or 0 if they
	 *         have the same priority.
	 * @see org.scijava.util.ClassUtils#compare(Class, Class)
	 */
	public static int compare(final Prioritized p1, final Prioritized p2) {
		final double priority1 =
			p1 == null ? Double.NEGATIVE_INFINITY : p1.getPriority();
		final double priority2 =
			p2 == null ? Double.NEGATIVE_INFINITY : p2.getPriority();
		if (priority1 == priority2) return 0;
		// NB: We invert the ordering here, so that large values come first,
		// rather than the typical natural ordering of smaller values first.
		return priority1 > priority2 ? -1 : 1;
	}

	/**
	 * Injects the specified priority into the given object. Note that this is
	 * only possible if the given object implements the {@link Prioritized}
	 * interface.
	 * 
	 * @param o The object to which the priority should be assigned.
	 * @return true If the priority was successfully injected.
	 */
	public static boolean inject(final Object o, final double priority) {
		if (!(o instanceof Prioritized)) return false;
		((Prioritized) o).setPriority(priority);
		return true;
	}

}
