/*
    * 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.rotation;
  
  import org.apache.commons.geometry.euclidean.EuclideanTransform;
  import org.apache.commons.geometry.euclidean.internal.Vectors;
  import org.apache.commons.geometry.euclidean.twod.AffineTransformMatrix2D;
  import org.apache.commons.geometry.euclidean.twod.Vector2D;
  
  /** Class representing a rotation in 2 dimensional Euclidean space. Positive
   * rotations are in a <em>counter-clockwise</em> direction.
   */
  public final class Rotation2D implements EuclideanTransform<Vector2D> {
  
      /** Instance representing a rotation of zero radians. */
      private static final Rotation2D IDENTITY = new Rotation2D(0);
  
      /** The angle of the rotation in radians. */
      private final double angle;
  
      /** The cosine of the angle of rotation, cached to avoid repeated computation. */
      private final double cosAngle;
  
      /** The sine of the angle of rotation, cached to avoid repeated computation. */
      private final double sinAngle;
  
      /** Create a new instance representing the given angle.
       * @param angle the angle of rotation, in radians
       */
      private Rotation2D(final double angle) {
          this.angle = angle;
          this.cosAngle = Math.cos(angle);
          this.sinAngle = Math.sin(angle);
      }
  
      /** Get the angle of rotation in radians.
       * @return the angle of rotation in radians
       */
      public double getAngle() {
          return angle;
      }
  
      /** {@inheritDoc} */
      @Override
      public Rotation2D inverse() {
          return new Rotation2D(-angle);
      }
  
      /** {@inheritDoc}
       *
       * <p>This method simply returns true since rotations always preserve the orientation
       * of the space.</p>
       */
      @Override
      public boolean preservesOrientation() {
          return true;
      }
  
      /** {@inheritDoc} */
      @Override
      public Vector2D apply(final Vector2D pt) {
          final double x = pt.getX();
          final double y = pt.getY();
  
          return Vector2D.of(
                      (x * cosAngle) - (y * sinAngle),
                      (x * sinAngle) + (y * cosAngle)
                  );
      }
  
      /** {@inheritDoc}
       *
       * <p>This method simply calls {@code apply(vec)} since rotations treat
       * points and vectors similarly.</p>
       * */
      @Override
      public Vector2D applyVector(final Vector2D vec) {
          return apply(vec);
      }
  
      /** Return an {@link AffineTransformMatrix2D} representing the same rotation
       * as this instance.
       * @return a transform matrix representing the same rotation
       */
      public AffineTransformMatrix2D toMatrix() {
         return AffineTransformMatrix2D.of(
                     cosAngle, -sinAngle, 0.0,
                     sinAngle, cosAngle, 0.0
                 );
     }
 
     /** {@inheritDoc} */
     @Override
     public int hashCode() {
         return Double.hashCode(angle);
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean equals(final Object obj) {
         if (this == obj) {
             return true;
         }
         if (!(obj instanceof Rotation2D)) {
             return false;
         }
 
         final Rotation2D other = (Rotation2D) obj;
 
         return Double.compare(this.angle, other.angle) == 0;
     }
 
     /** {@inheritDoc} */
     @Override
     public String toString() {
         final StringBuilder sb = new StringBuilder();
         sb.append(this.getClass().getSimpleName())
             .append("[angle=")
             .append(angle)
             .append(']');
 
         return sb.toString();
     }
 
     /** Create a new instance with the given angle of rotation.
      * @param angle the angle of rotation in radians
      * @return a new instance with the given angle of rotation
      */
     public static Rotation2D of(final double angle) {
         return new Rotation2D(angle);
     }
 
     /** Return an instance representing the identity rotation, ie a rotation
      * of zero radians.
      * @return an instance representing a rotation of zero radians
      */
     public static Rotation2D identity() {
         return IDENTITY;
     }
 
     /** Create a rotation instance that rotates the vector {@code u} to point in the direction of
      * vector {@code v}.
      * @param u input vector
      * @param v target vector
      * @return a rotation instance that rotates {@code u} to point in the direction of {@code v}
      * @throws IllegalArgumentException if either vector cannot be normalized
      */
     public static Rotation2D createVectorRotation(final Vector2D u, final Vector2D v) {
         // make sure that the vectors are real-valued and of non-zero length; we don't
         // actually need to use the norm value; we just need to check its properties
         Vectors.checkedNorm(u);
         Vectors.checkedNorm(v);
 
         final double uAzimuth = Math.atan2(u.getY(), u.getX());
         final double vAzimuth = Math.atan2(v.getY(), v.getX());
 
         return of(vAzimuth - uAzimuth);
     }
 }