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Geometric primitives for euclidean space.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.geometry.euclidean.twod;

import org.apache.commons.geometry.core.RegionLocation;
import org.apache.commons.geometry.core.Transform;
import org.apache.commons.geometry.core.partitioning.Split;
import org.apache.commons.numbers.core.Precision;

/** Class representing a portion of a line in 2D Euclidean space that starts at infinity and
 * continues in the direction of the line up to a single end point. This is equivalent to taking a
 * {@link Ray} and reversing the line direction.
 *
 * Instances of this class are guaranteed to be immutable.
 * @see Ray
 * @see Lines
 */
public final class ReverseRay extends LineConvexSubset {

    /** The end point of the reverse ray. */
    private final Vector2D endPoint;

    /** Construct a new instance from the given line and end point. Callers are responsible for ensuring that
     * the given end point lies on the line. No validation is performed.
     * @param line line for the instance
     * @param endPoint end point for the instance
     */
    ReverseRay(final Line line, final Vector2D endPoint) {
        super(line);

        this.endPoint = endPoint;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@code false}.
     */
    @Override
    public boolean isFull() {
        return false;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@code true}.
     */
    @Override
    public boolean isInfinite() {
        return true;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@code false}.
     */
    @Override
    public boolean isFinite() {
        return false;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@link Double#POSITIVE_INFINITY}.
     */
    @Override
    public double getSize() {
        return Double.POSITIVE_INFINITY;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@code null}.
     */
    @Override
    public Vector2D getCentroid() {
        return null;
    }

    /** {@inheritDoc}
     *
     * This method always returns {@code null}.
     */
    @Override
    public Vector2D getStartPoint() {
        return null;
    }

    /** {@inheritDoc}
    *
    * This method always returns {@link Double#NEGATIVE_INFINITY}.
    */
    @Override
    public double getSubspaceStart() {
        return Double.NEGATIVE_INFINITY;
    }

    /** {@inheritDoc} */
    @Override
    public Vector2D getEndPoint() {
        return endPoint;
    }

    /** {@inheritDoc} */
    @Override
    public double getSubspaceEnd() {
        return getLine().abscissa(endPoint);
    }

    /** {@inheritDoc}
    *
    * This method always returns {@code null}.
    */
    @Override
    public Bounds2D getBounds() {
        return null; // infinite; no bounds
    }

    /** {@inheritDoc} */
    @Override
    public ReverseRay transform(final Transform transform) {
        final Line tLine = getLine().transform(transform);
        final Vector2D tEnd = transform.apply(getEndPoint());

        return new ReverseRay(tLine, tEnd);
    }

    /** {@inheritDoc} */
    @Override
    public Ray reverse() {
        return new Ray(getLine().reverse(), endPoint);
    }

    /** {@inheritDoc} */
    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        sb.append(getClass().getSimpleName())
            .append("[direction= ")
            .append(getLine().getDirection())
            .append(", endPoint= ")
            .append(getEndPoint())
            .append(']');

        return sb.toString();
    }

    /** {@inheritDoc} */
    @Override
    RegionLocation classifyAbscissa(final double abscissa) {
        final int cmp = getPrecision().compare(abscissa, getSubspaceEnd());
        if (cmp < 0) {
            return RegionLocation.INSIDE;
        } else if (cmp == 0) {
            return RegionLocation.BOUNDARY;
        }

        return RegionLocation.OUTSIDE;
    }

    /** {@inheritDoc} */
    @Override
    double closestAbscissa(final double abscissa) {
        return Math.min(getSubspaceEnd(), abscissa);
    }

    /** {@inheritDoc} */
    @Override
    protected Split splitOnIntersection(final Line splitter, final Vector2D intersection) {
        final Line line = getLine();
        final Precision.DoubleEquivalence splitterPrecision = splitter.getPrecision();

        final int endCmp = splitterPrecision.compare(splitter.offset(endPoint), 0.0);
        final boolean pointsTowardPlus = splitter.getOffsetDirection().dot(line.getDirection()) >= 0.0;

        if (pointsTowardPlus && endCmp < 1) {
            // entirely on minus side
            return new Split<>(this, null);
        } else if (!pointsTowardPlus && endCmp > -1) {
            // entirely on plus side
            return new Split<>(null, this);
        }

        // we're going to be split
        final Segment splitSeg = new Segment(line, intersection, endPoint);
        final ReverseRay splitRevRay = new ReverseRay(line, intersection);

        final LineConvexSubset minus = (endCmp > 0) ? splitRevRay : splitSeg;
        final LineConvexSubset plus = (endCmp > 0) ? splitSeg : splitRevRay;

        return new Split<>(minus, plus);
    }
}