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/*******************************************************************************
 * Copyright (c) 2010 Research Group Software Construction, RWTH Aachen University and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Alexander Nyßen (Research Group Software Contruction, RWTH Aachen University) - initial API and implementation
 *     
 *******************************************************************************/
package org.eclipse.draw2d.geometry;

/**
 * Represents a straight line within 2-dimensional Euclidean space.
 * 
 * @author Alexander Nyssen
 * @since 3.6
 */
public class Straight {

	/** position vector of this straight */
	public Vector position;

	/** direction vector of this straight */
	public Vector direction;

	/**
	 * Constructs a new Straight with the given position and direction.
	 * 
	 * @param position
	 * @param direction
	 */
	public Straight(Vector position, Vector direction) {
		if (direction.isNull()) {
			throw new IllegalArgumentException(
					"direction has to be unequal to (0,0)"); //$NON-NLS-1$
		}
		this.position = position;
		this.direction = direction;
	}

	/**
	 * Constructs a new Straight between the two given Points.
	 * 
	 * @param point1
	 *            a first waypoint of the Straight to be constructed
	 * @param point2
	 *            a second waypoint of the Straight to be constructed
	 */
	public Straight(PrecisionPoint point1, PrecisionPoint point2) {
		this(new Vector(point1), new Vector(point1, point2));
	}

	/**
	 * Checks whether this Straight and the provided one have an intersection
	 * point.
	 * 
	 * @param other
	 *            The Straight to use for the calculation.
	 * @return true if the two Straights intersect, false otherwise.
	 */
	public boolean intersects(Straight other) {
		return direction.getDotProduct(other.direction
				.getOrthogonalComplement()) != 0;
	}

	/**
	 * Checks whether this Straight and the provided one have an intersection
	 * point, which is inside the specified segment between segmentStart and
	 * segmentEnd.
	 * 
	 * segmentStart a Vector indicating the start point of the segment. Has to
	 * be a point on the straight.
	 * 
	 * @param segmentEnd
	 *            a Vector indicating the end point of the segment. Has to be a
	 *            point on the straight.
	 * @param other
	 *            the Straight to test
	 * @return true if the true straights intersect and the intersection point
	 *         is contained within the specified segment, false otherwise.
	 * @since 3.2
	 */
	public boolean intersectsWithinSegment(Vector segmentStart,
			Vector segmentEnd, Straight other) {
		// precondition: segment start and end have to be points on this
		// straight.
		if (!contains(segmentStart) || !contains(segmentEnd)) {
			throw new IllegalArgumentException(
					"segment points have to be contained"); //$NON-NLS-1$
		}

		// check if segmentStart->segmentEnd is a legal segment or a single
		// point
		Vector segmentDirection = segmentEnd.getSubtracted(segmentStart);
		if (segmentDirection.isNull()) {
			return other.contains(segmentStart);
		}

		// legal segment, check if there is an intersection within the segment
		if (intersects(other)) {
			Vector intersection = getIntersection(other);
			return containsWithinSegment(segmentStart, segmentEnd, intersection);
		}
		return false;
	}

	/**
	 * Computes the intersection point of this Straight and the provided one, if
	 * it exists.
	 * 
	 * @param other
	 *            The Straight to use for calculations.
	 * @return A Vector pointing to the intersection point, if it exists, null
	 *         if no intersection point exists (or the Straights are equal).
	 */
	public Vector getIntersection(Straight other) {
		// first check if there is a single intersection point
		if (!intersects(other)) {
			return null;
		}
		// calculate intersection point
		Vector s1 = direction.getMultiplied(other.position
				.getDotProduct(other.direction.getOrthogonalComplement()));
		Vector s2 = other.direction.getMultiplied(position
				.getDotProduct(direction.getOrthogonalComplement()));
		return s1.getSubtracted(s2).getDivided(
				direction.getDotProduct(other.direction
						.getOrthogonalComplement()));
	}

	/**
	 * Returns the (smallest) angle between this Straight and the provided one.
	 * 
	 * @param other
	 *            The Straight to be used for the calculation.
	 * @return The angle spanned between the two Straights.
	 */
	public double getAngle(Straight other) {
		return direction.getAngle(other.direction);
	}

	/**
	 * Returns the projection of the given Vector onto this Straight, which is
	 * the point on this Straight with the minimal distance to the point,
	 * denoted by the provided Vector.
	 * 
	 * @param vector
	 *            The Vector whose projection should be determined.
	 * @return A new Vector representing the projection of the provided Vector
	 *         onto this Straight.
	 */
	public Vector getProjection(Vector vector) {
		return getIntersection(new Straight(vector,
				direction.getOrthogonalComplement()));
	}

	/**
	 * Returns the distance of the provided Vector to this Straight, which is
	 * the distance between the provided Vector and its projection onto this
	 * Straight.
	 * 
	 * @param vector
	 *            The Vector whose distance is to be calculated.
	 * @return the distance between this Straight and the provided Vector.
	 */
	public double getDistance(Vector vector) {
		return getProjection(vector).getSubtracted(vector).getLength();
	}

	/**
	 * Calculates whether the point indicated by the provided Vector is a point
	 * on this Straight.
	 * 
	 * @param vector
	 *            the Vector who has to be checked.
	 * @return true if the point indicated by the given Vector is a point of
	 *         this Straight, false otherwise.
	 */
	public boolean contains(Vector vector) {
		return getDistance(vector) == 0;
	}

	/**
	 * Calculates whether the point indicated by the provided Vector is a point
	 * on the straight segment between the given start and end points.
	 * 
	 * @param segmentStart
	 *            a Vector indicating the start point of the segment. Has to be
	 *            a point on the straight.
	 * @param segmentEnd
	 *            a Vector indicating the end point of the segment. Has to be a
	 *            point on the straight.
	 * @param vector
	 *            the Vector who has to be checked.
	 * @return true if point indicated by the given Vector is a point on this
	 *         straight, within the specified segment, false otherwise.
	 */
	public boolean containsWithinSegment(Vector segmentStart,
			Vector segmentEnd, Vector vector) {
		// precondition: segment start and end have to be points on this
		// straight.
		if (!contains(segmentStart) || !contains(segmentEnd)) {
			throw new IllegalArgumentException(
					"segment points have to be contained"); //$NON-NLS-1$
		}

		// check if segmentStart->segmentEnd is a legal segment or a single
		// point
		Vector segmentDirection = segmentEnd.getSubtracted(segmentStart);
		if (segmentDirection.isNull()) {
			return segmentStart.equals(vector);
		}

		// legal segment
		if (new Straight(segmentStart, segmentDirection).contains(vector)) {
			// compute parameter s, so that vector = segmentStart + s *
			// (segmentEnd - segmentStart).
			double s = segmentDirection.isVertical() ? (vector.y - segmentStart.y)
					/ segmentDirection.y
					: (vector.x - segmentStart.x) / segmentDirection.x;
			// if s is between 0 and 1, intersection point lies within
			// segment
			if (0 <= s && s <= 1) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Checks whether this Straight and the provided one are parallel to each
	 * other.
	 * 
	 * @param other
	 *            The Straight to test for parallelism.
	 * @return true if the direction vectors of this Straight and the provided
	 *         one are parallel, false otherwise.
	 */
	public boolean isParallelTo(Straight other) {
		return direction.isParallelTo(other.direction);
	}

	/**
	 * Checks whether this Straight is equal to the provided Straight. Two
	 * Straights s1 and s2 are equal, if the position vector of s2 is a point on
	 * s1 and the direction vectors of s1 and s2 are parallel.
	 * 
	 * @see java.lang.Object#equals(java.lang.Object)
	 */
	public boolean equals(Object other) {
		if (!(other instanceof Straight)) {
			return false;
		} else {
			Straight otherStraight = (Straight) other;
			return contains(otherStraight.position)
					&& isParallelTo(otherStraight);
		}
	}

	/**
	 * @see java.lang.Object#hashCode()
	 */
	public int hashCode() {
		return position.hashCode() + direction.hashCode();
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	public String toString() {
		return position.toString() + " + s * " + direction.toString(); //$NON-NLS-1$
	}

}