/*
    * 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.spherical.oned;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.List;
  import java.util.Objects;
  
  import org.apache.commons.geometry.core.Transform;
  import org.apache.commons.geometry.core.partitioning.Hyperplane;
  import org.apache.commons.geometry.core.partitioning.HyperplaneLocation;
  import org.apache.commons.geometry.core.partitioning.HyperplaneSubset;
  import org.apache.commons.geometry.core.partitioning.Split;
  import org.apache.commons.geometry.core.partitioning.bsp.AbstractBSPTree;
  import org.apache.commons.geometry.core.partitioning.bsp.AbstractRegionBSPTree;
  import org.apache.commons.geometry.euclidean.twod.Vector2D;
  import org.apache.commons.numbers.angle.Angle;
  import org.apache.commons.numbers.core.Precision;
  
  /** BSP tree representing regions in 1D spherical space.
   */
  public class RegionBSPTree1S extends AbstractRegionBSPTree<Point1S, RegionBSPTree1S.RegionNode1S> {
      /** Comparator used to sort BoundaryPairs by ascending azimuth.  */
      private static final Comparator<BoundaryPair> BOUNDARY_PAIR_COMPARATOR =
              Comparator.comparingDouble(BoundaryPair::getMinValue);
  
      /** Create a new, empty instance.
       */
      public RegionBSPTree1S() {
          this(false);
      }
  
      /** Create a new region. If {@code full} is true, then the region will
       * represent the entire circle. Otherwise, it will be empty.
       * @param full whether or not the region should contain the entire
       *      circle or be empty
       */
      public RegionBSPTree1S(final boolean full) {
          super(full);
      }
  
      /** Return a deep copy of this instance.
       * @return a deep copy of this instance.
       * @see #copy(org.apache.commons.geometry.core.partitioning.bsp.BSPTree)
       */
      public RegionBSPTree1S copy() {
          final RegionBSPTree1S result = RegionBSPTree1S.empty();
          result.copy(this);
  
          return result;
      }
  
      /** Add an interval to this region. The resulting region will be the
       * union of the interval and the region represented by this instance.
       * @param interval the interval to add
       */
      public void add(final AngularInterval interval) {
          union(fromInterval(interval));
      }
  
      /** {@inheritDoc} */
      @Override
      public Point1S project(final Point1S pt) {
          final BoundaryProjector1S projector = new BoundaryProjector1S(pt);
          accept(projector);
  
          return projector.getProjected();
      }
  
      /** {@inheritDoc}
       *
       * <p>Each interval of the region is transformed individually and the
       * results are unioned. If the size of any transformed interval is greater
       * than or equal to 2pi, then the region is set to the full space.</p>
       */
      @Override
      public void transform(final Transform<Point1S> transform) {
          if (!isFull() && !isEmpty()) {
              // transform each interval individually to handle wrap-around
              final List<AngularInterval> intervals = toIntervals();
  
              setEmpty();
  
             for (final AngularInterval interval : intervals) {
                 union(interval.transform(transform).toTree());
             }
         }
     }
 
     /** {@inheritDoc}
      *
      * <p>It is important to note that split operations occur according to the rules of the
      * {@link CutAngle} hyperplane class. In this class, the continuous circle is viewed
      * as a non-circular segment of the number line in the range {@code [0, 2pi)}. Hyperplanes
      * are placed along this line and partition it into the segments {@code [0, x]}
      * and {@code [x, 2pi)}, where {@code x} is the location of the hyperplane. For example,
      * a positive-facing {@link CutAngle} instance with an azimuth of {@code 0.5pi} has
      * a minus side consisting of the angles {@code [0, 0.5pi]} and a plus side consisting of
      * the angles {@code [0.5pi, 2pi)}. Similarly, a positive-facing {@link CutAngle} with
      * an azimuth of {@code 0pi} has a plus side of {@code [0, 2pi)} (the full space) and
      * a minus side that is completely empty (since no points exist in our domain that are
      * less than zero). These rules can result in somewhat non-intuitive behavior at times.
      * For example, splitting a non-empty region with a hyperplane at {@code 0pi} is
      * essentially a no-op, since the region will either lie entirely on the plus or minus
      * side of the hyperplane (depending on the hyperplane's orientation) regardless of the actual
      * content of the region. In these situations, a copy of the tree is returned on the
      * appropriate side of the split.</p>
      *
      * @see CutAngle
      * @see #splitDiameter(CutAngle)
      */
     @Override
     public Split<RegionBSPTree1S> split(final Hyperplane<Point1S> splitter) {
         // Handle the special case where the cut is on the azimuth equivalent to zero.
         // In this case, it is not possible for any points to lie between it and zero.
         if (!isEmpty() && splitter.classify(Point1S.ZERO) == HyperplaneLocation.ON) {
             final CutAngle cut = (CutAngle) splitter;
             if (cut.isPositiveFacing()) {
                 return new Split<>(null, copy());
             } else {
                 return new Split<>(copy(), null);
             }
         }
 
         return split(splitter, RegionBSPTree1S.empty(), RegionBSPTree1S.empty());
     }
 
     /** Split the instance along a circle diameter.The diameter is defined by the given
      * split point and its reversed antipodal point.
      * @param splitter split point defining one side of the split diameter
      * @return result of the split operation
      */
     public Split<RegionBSPTree1S> splitDiameter(final CutAngle splitter) {
 
         final CutAngle opposite = CutAngles.fromPointAndDirection(
                 splitter.getPoint().antipodal(),
                 !splitter.isPositiveFacing(),
                 splitter.getPrecision());
 
         final double plusPoleOffset = splitter.isPositiveFacing() ?
                 +Angle.PI_OVER_TWO :
                 -Angle.PI_OVER_TWO;
         final Point1S plusPole = Point1S.of(splitter.getAzimuth() + plusPoleOffset);
 
         final boolean zeroOnPlusSide = splitter.getPrecision()
                 .lte(plusPole.distance(Point1S.ZERO), Angle.PI_OVER_TWO);
 
         final Split<RegionBSPTree1S> firstSplit = split(splitter);
         final Split<RegionBSPTree1S> secondSplit = split(opposite);
 
         RegionBSPTree1S minus = RegionBSPTree1S.empty();
         RegionBSPTree1S plus = RegionBSPTree1S.empty();
 
         if (zeroOnPlusSide) {
             // zero wrap-around needs to be handled on the plus side of the split
             safeUnion(plus, firstSplit.getPlus());
             safeUnion(plus, secondSplit.getPlus());
 
             minus = firstSplit.getMinus();
             if (minus != null) {
                 minus = minus.split(opposite).getMinus();
             }
         } else {
             // zero wrap-around needs to be handled on the minus side of the split
             safeUnion(minus, firstSplit.getMinus());
             safeUnion(minus, secondSplit.getMinus());
 
             plus = firstSplit.getPlus();
             if (plus != null) {
                 plus = plus.split(opposite).getPlus();
             }
         }
 
         return new Split<>(
                 (minus != null && !minus.isEmpty()) ? minus : null,
                 (plus != null && !plus.isEmpty()) ? plus : null);
     }
 
 
     /** Convert the region represented by this tree into a list of separate
      * {@link AngularInterval}s, arranged in order of ascending min value.
      * @return list of {@link AngularInterval}s representing this region in order of
      *      ascending min value
      */
     public List<AngularInterval> toIntervals() {
         if (isFull()) {
             return Collections.singletonList(AngularInterval.full());
         }
 
         final List<BoundaryPair> insideBoundaryPairs = new ArrayList<>();
         for (final RegionNode1S node : nodes()) {
             if (node.isInside()) {
                 insideBoundaryPairs.add(getNodeBoundaryPair(node));
             }
         }
 
         insideBoundaryPairs.sort(BOUNDARY_PAIR_COMPARATOR);
 
         final int boundaryPairCount = insideBoundaryPairs.size();
 
         // Get the start point for merging intervals together.
         final int startOffset = getIntervalStartIndex(insideBoundaryPairs);
 
         // Go through the pairs starting at the start offset and create intervals
         // for each set of adjacent pairs.
         final List<AngularInterval> intervals = new ArrayList<>();
 
         BoundaryPair start = null;
         BoundaryPair end = null;
         BoundaryPair current;
 
         for (int i = 0; i < boundaryPairCount; ++i) {
             current = insideBoundaryPairs.get((i + startOffset) % boundaryPairCount);
 
             if (start == null) {
                 start = current;
                 end = current;
             } else if (Objects.equals(end.getMax(), current.getMin())) {
                 // these intervals should be merged
                 end = current;
             } else {
                 // these intervals should be separate
                 intervals.add(createInterval(start, end));
 
                 // queue up the next pair
                 start = current;
                 end = current;
             }
         }
 
         if (start != null && end != null) {
             intervals.add(createInterval(start, end));
         }
 
         return intervals;
     }
 
     /** Get the index that should be used as the starting point for combining adjacent boundary pairs
      * into contiguous intervals. This is computed as the first boundary pair found that is not connected
      * to the pair before it, or {@code 0} if no such entry exists.
      * @param boundaryPairs list of boundary pairs to search; must be ordered by increasing azimuth
      * @return the index to use as a starting place for combining adjacent boundary pairs
      *      into contiguous intervals
      */
     private int getIntervalStartIndex(final List<BoundaryPair> boundaryPairs) {
         final int size = boundaryPairs.size();
 
         if (size > 0) {
             BoundaryPair current;
             BoundaryPair previous = boundaryPairs.get(size - 1);
 
             for (int i = 0; i < size; ++i, previous = current) {
                 current = boundaryPairs.get(i);
 
                 if (!Objects.equals(current.getMin(), previous.getMax())) {
                     return i;
                 }
             }
         }
 
         return 0;
     }
 
     /** Create an interval instance from the min boundary from the start boundary pair and
      * the max boundary from the end boundary pair. The hyperplane directions are adjusted
      * as needed.
      * @param start starting boundary pair
      * @param end ending boundary pair
      * @return an interval created from the min boundary of the given start pair and the
      *      max boundary from the given end pair
      */
     private AngularInterval createInterval(final BoundaryPair start, final BoundaryPair end) {
         CutAngle min = start.getMin();
         CutAngle max = end.getMax();
 
         final Precision.DoubleEquivalence precision = (min != null) ? min.getPrecision() : max.getPrecision();
 
         // flip the hyperplanes if needed since there's no
         // guarantee that the inside will be on the minus side
         // of the hyperplane (for example, if the region is complemented)
 
         if (min != null) {
             if (min.isPositiveFacing()) {
                 min = min.reverse();
             }
         } else {
             min = CutAngles.createNegativeFacing(0.0, precision);
         }
 
         if (max != null) {
             if (!max.isPositiveFacing()) {
                 max = max.reverse();
             }
         } else {
             max = CutAngles.createPositiveFacing(Angle.TWO_PI, precision);
         }
 
         return AngularInterval.of(min, max);
     }
 
     /** Return the min/max boundary pair for the convex region represented by the given node.
      * @param node the node to compute the interval for
      * @return the min/max boundary pair for the convex region represented by the given node
      */
     private BoundaryPair getNodeBoundaryPair(final RegionNode1S node) {
         CutAngle min = null;
         CutAngle max = null;
 
         CutAngle pt;
         RegionNode1S child = node;
         RegionNode1S parent;
 
         while ((min == null || max == null) && (parent = child.getParent()) != null) {
             pt = (CutAngle) parent.getCutHyperplane();
 
             if ((pt.isPositiveFacing() && child.isMinus()) ||
                     (!pt.isPositiveFacing() && child.isPlus())) {
 
                 if (max == null) {
                     max = pt;
                 }
             } else if (min == null) {
                 min = pt;
             }
 
             child = parent;
         }
 
         return new BoundaryPair(min, max);
     }
 
     /** {@inheritDoc} */
     @Override
     protected RegionSizeProperties<Point1S> computeRegionSizeProperties() {
         if (isFull()) {
             return new RegionSizeProperties<>(Angle.TWO_PI, null);
         } else if (isEmpty()) {
             return new RegionSizeProperties<>(0, null);
         }
 
         double size = 0;
         Vector2D scaledCentroidSum = Vector2D.ZERO;
 
         double intervalSize;
 
         for (final AngularInterval interval : toIntervals()) {
             intervalSize = interval.getSize();
 
             size += intervalSize;
             scaledCentroidSum = scaledCentroidSum.add(interval.getCentroid().getVector().withNorm(intervalSize));
         }
 
         final Precision.DoubleEquivalence precision = ((CutAngle) getRoot().getCutHyperplane()).getPrecision();
 
         final Point1S centroid = scaledCentroidSum.eq(Vector2D.ZERO, precision) ?
                  null :
                  Point1S.from(scaledCentroidSum);
 
         return new RegionSizeProperties<>(size, centroid);
     }
 
     /** {@inheritDoc} */
     @Override
     protected RegionNode1S createNode() {
         return new RegionNode1S(this);
     }
 
     /** Return a new, empty BSP tree.
      * @return a new, empty BSP tree.
      */
     public static RegionBSPTree1S empty() {
         return new RegionBSPTree1S(false);
     }
 
     /** Return a new, full BSP tree. The returned tree represents the
      * full space.
      * @return a new, full BSP tree.
      */
     public static RegionBSPTree1S full() {
         return new RegionBSPTree1S(true);
     }
 
     /** Return a new BSP tree representing the same region as the given angular interval.
      * @param interval the input interval
      * @return a new BSP tree representing the same region as the given angular interval
      */
     public static RegionBSPTree1S fromInterval(final AngularInterval interval) {
         final CutAngle minBoundary = interval.getMinBoundary();
         final CutAngle maxBoundary = interval.getMaxBoundary();
 
         final RegionBSPTree1S tree = full();
 
         if (minBoundary != null) {
             tree.insert(minBoundary.span());
         }
 
         if (maxBoundary != null) {
             tree.insert(maxBoundary.span());
         }
 
         return tree;
     }
 
     /** Perform a union operation with {@code target} and {@code input}, storing the result
      * in {@code target}; does nothing if {@code input} is null.
      * @param target target tree
      * @param input input tree
      */
     private static void safeUnion(final RegionBSPTree1S target, final RegionBSPTree1S input) {
         if (input != null) {
             target.union(input);
         }
     }
 
     /** BSP tree node for one dimensional spherical space.
      */
     public static final class RegionNode1S extends AbstractRegionBSPTree.AbstractRegionNode<Point1S, RegionNode1S> {
         /** Simple constructor.
          * @param tree the owning tree instance
          */
         private RegionNode1S(final AbstractBSPTree<Point1S, RegionNode1S> tree) {
             super(tree);
         }
 
         /** {@inheritDoc} */
         @Override
         protected RegionNode1S getSelf() {
             return this;
         }
     }
 
     /** Internal class containing pairs of interval boundaries.
      */
     private static final class BoundaryPair {
 
         /** The min boundary. */
         private final CutAngle min;
 
         /** The max boundary. */
         private final CutAngle max;
 
         /** Simple constructor.
          * @param min min boundary hyperplane
          * @param max max boundary hyperplane
          */
         BoundaryPair(final CutAngle min, final CutAngle max) {
             this.min = min;
             this.max = max;
         }
 
         /** Get the minimum boundary hyperplane.
          * @return the minimum boundary hyperplane.
          */
         public CutAngle getMin() {
             return min;
         }
 
         /** Get the maximum boundary hyperplane.
          * @return the maximum boundary hyperplane.
          */
         public CutAngle getMax() {
             return max;
         }
 
         /** Get the minimum value of the interval or zero if no minimum value exists.
          * @return the minimum value of the interval or zero
          *      if no minimum value exists.
          */
         public double getMinValue() {
             return (min != null) ? min.getNormalizedAzimuth() : 0;
         }
     }
 
     /** Class used to project points onto the region boundary.
      */
     private static final class BoundaryProjector1S extends BoundaryProjector<Point1S, RegionNode1S> {
         /** Simple constructor.
          * @param point the point to project onto the region's boundary
          */
         BoundaryProjector1S(final Point1S point) {
             super(point);
         }
 
         /** {@inheritDoc} */
         @Override
         protected boolean isPossibleClosestCut(final HyperplaneSubset<Point1S> cut, final Point1S target,
                 final double minDist) {
             // since the space wraps around, consider any cut as possibly being the closest
             return true;
         }
 
         /** {@inheritDoc} */
         @Override
         protected Point1S disambiguateClosestPoint(final Point1S target, final Point1S a, final Point1S b) {
             // prefer the point with the smaller normalize azimuth value
             return a.getNormalizedAzimuth() < b.getNormalizedAzimuth() ? a : b;
         }
     }
 }