/* Contributed in the public domain.
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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.orekit;
  
  import org.hamcrest.Description;
  import org.hamcrest.Matcher;
  import org.hamcrest.Matchers;
  import org.hamcrest.SelfDescribing;
  import org.hamcrest.TypeSafeDiagnosingMatcher;
  import org.hamcrest.TypeSafeMatcher;
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.FieldElement;
  import org.hipparchus.dfp.Dfp;
  import org.hipparchus.geometry.euclidean.threed.Rotation;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.linear.RealMatrix;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.Precision;
  import org.orekit.attitudes.Attitude;
  import org.orekit.bodies.GeodeticPoint;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.Constants;
  import org.orekit.utils.PVCoordinates;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  
  import static org.hamcrest.CoreMatchers.is;
  import static org.hamcrest.Matchers.array;
  
  /**
   * A set of matchers specific to the Orekit value classes.
   *
   * @author Evan Ward
   */
  public class OrekitMatchers {
  
      /**
       * Match a geodetic point
       *
       * @param lat latitude matcher, in radians
       * @param lon longitude matcher, in radians
       * @param alt altitude matcher, in meters
       * @return a {@link GeodeticPoint} matcher
       */
      public static Matcher<GeodeticPoint> geodeticPoint(
              final Matcher<Double> lat,
              final Matcher<Double> lon,
              final Matcher<Double> alt) {
          return new TypeSafeDiagnosingMatcher<GeodeticPoint>() {
              @Override
              public void describeTo(Description description) {
                  description.appendList("GeodeticPoint[", ", ", "]",
                          Arrays.<SelfDescribing>asList(lat, lon, alt));
              }
  
              @Override
              protected boolean matchesSafely(GeodeticPoint item,
                                              Description mismatchDescription) {
                  if (!lat.matches(item.getLatitude())) {
                      mismatchDescription.appendText("the latitude ");
                      lat.describeMismatch(item.getLatitude(),
                              mismatchDescription);
                      return false;
                  }
                  if (!lon.matches(item.getLongitude())) {
                      mismatchDescription.appendText("the longitude ");
                      lon.describeMismatch(item.getLongitude(),
                              mismatchDescription);
                      return false;
                  }
                  if (!alt.matches(item.getAltitude())) {
                      mismatchDescription.appendText("the altitude ");
                      alt.describeMismatch(item.getAltitude(),
                              mismatchDescription);
                      return false;
                  }
                  return true;
              }
          };
      }
  
      /**
       * Match a geodetic point
      *
      * @param lat latitude, in radians
      * @param lon longitude, in radians
      * @param alt altitude, in meters
      * @return matcher of a {@link GeodeticPoint}
      */
     public static Matcher<GeodeticPoint> geodeticPoint(double lat,
                                                        double lon,
                                                        double alt) {
         return geodeticPoint(is(lat), is(lon), is(alt));
     }
 
     /**
      * Match a geodetic point by comparing it with another one.
      *
      * @param expected the expected value
      * @param absTol   the absolute tolerance on the comparison, in meters.
      *                 Differences less than this value will be ignored.
      * @return a {@link GeodeticPoint} matcher
      */
     public static Matcher<GeodeticPoint> geodeticPointCloseTo(
             GeodeticPoint expected, double absTol) {
         double angularAbsTol = absTol / Constants.WGS84_EARTH_EQUATORIAL_RADIUS;
         return geodeticPoint(closeTo(expected.getLatitude(), angularAbsTol),
                 closeTo(expected.getLongitude(), angularAbsTol),
                 closeTo(expected.getAltitude(), absTol));
     }
 
     /**
      * Match a geodetic point by comparing it with another one.
      *
      * @param expected the expected value
      * @param ulps     the ulps difference allowed
      * @return a {@link GeodeticPoint} matcher
      * @see #relativelyCloseTo
      */
     public static Matcher<GeodeticPoint> geodeticPointCloseTo(
             GeodeticPoint expected, int ulps) {
         return geodeticPoint(relativelyCloseTo(expected.getLatitude(), ulps),
                 relativelyCloseTo(expected.getLongitude(), ulps),
                 relativelyCloseTo(expected.getAltitude(), ulps));
     }
 
     /**
      * Matches a {@link Vector3D} based on its three coordinates.
      *
      * @param x matcher for the x coordinate
      * @param y matcher for the y coordinate
      * @param z matcher for the z coordinate
      * @return a vector matcher
      */
     public static Matcher<Vector3D> vector(final Matcher<Double> x,
                                            final Matcher<Double> y,
                                            final Matcher<Double> z) {
         return new TypeSafeDiagnosingMatcher<Vector3D>() {
             @Override
             public void describeTo(Description description) {
                 description.appendList("Vector3D[", ", ", "]",
                         Arrays.<SelfDescribing>asList(x, y, z));
             }
 
             @Override
             protected boolean matchesSafely(Vector3D item,
                                             Description mismatchDescription) {
                 if (!x.matches(item.getX())) {
                     mismatchDescription.appendText("the x coordinate ");
                     x.describeMismatch(item.getX(), mismatchDescription);
                     return false;
                 }
                 if (!y.matches(item.getY())) {
                     mismatchDescription.appendText("the y coordinate ");
                     y.describeMismatch(item.getY(), mismatchDescription);
                     return false;
                 }
                 if (!z.matches(item.getZ())) {
                     mismatchDescription.appendText("the z coordinate ");
                     z.describeMismatch(item.getZ(), mismatchDescription);
                     return false;
                 }
                 return true;
             }
         };
     }
 
     /**
      * Matches a {@link Vector3D} close to another one.
      *
      * @param vector the reference vector
      * @param absTol absolute tolerance of comparison, in each dimension
      * @return a vector matcher.
      */
     public static Matcher<Vector3D> vectorCloseTo(Vector3D vector, double absTol) {
         return vector(closeTo(vector.getX(), absTol),
                 closeTo(vector.getY(), absTol), closeTo(vector.getZ(), absTol));
     }
 
     /**
      * Matches a {@link Vector3D} close to another one.
      *
      * @param vector the reference vector
      * @param ulps   the relative tolerance, in units in last place, of the
      *               Comparison of each dimension.
      * @return a vector matcher.
      */
     public static Matcher<Vector3D> vectorCloseTo(Vector3D vector, int ulps) {
         return vector(relativelyCloseTo(vector.getX(), ulps),
                 relativelyCloseTo(vector.getY(), ulps),
                 relativelyCloseTo(vector.getZ(), ulps));
     }
 
     /**
      * Alias for {@link #vectorCloseTo(Vector3D, int)}
      *
      * @param x    the x component
      * @param y    the y component
      * @param z    the z component
      * @param ulps the relative tolerance, in ulps
      * @return a vector matcher
      */
     public static Matcher<Vector3D> vectorCloseTo(double x, double y, double z, int ulps) {
         return vectorCloseTo(new Vector3D(x, y, z), ulps);
     }
 
     /**
      * Matches a {@link Vector3D} to another one.
      *
      * @param vector the reference vector
      * @param absTol the absolute tolerance of comparison, in each dimension.
      * @param ulps   the relative tolerance of comparison in each dimension, in
      *               units in last place.
      * @return a matcher that matches if either the absolute or relative
      * comparison matches in each dimension.
      */
     public static Matcher<Vector3D> vectorCloseTo(Vector3D vector,
                                                   double absTol, int ulps) {
         return vector(numberCloseTo(vector.getX(), absTol, ulps),
                 numberCloseTo(vector.getY(), absTol, ulps),
                 numberCloseTo(vector.getZ(), absTol, ulps));
     }
 
     /**
      * Matches a {@link Vector3D} to another one.
      *
      * @param vector the reference vector
      * @param absTol the absolute tolerance of comparison, in each dimension.
      * @param relTol the relative tolerance of comparison, which is multiplied
      *               by {@code vector}'s magnitude.
      * @return a matcher that matches if either the absolute or relative
      * comparison matches in each dimension.
      */
     public static Matcher<Vector3D> vectorCloseTo(Vector3D vector,
                                                   double absTol,
                                                   double relTol) {
         final double tol = FastMath.max(absTol, relTol * vector.getNorm());
         return vector(
                 closeTo(vector.getX(), tol),
                 closeTo(vector.getY(), tol),
                 closeTo(vector.getZ(), tol));
     }
 
     /**
      * Match a {@link PVCoordinates}
      *
      * @param position matcher for the position
      * @param velocity matcher for the velocity
      * @return a matcher of {@link PVCoordinates}
      */
     public static Matcher<PVCoordinates> pvIs(
             final Matcher<? super Vector3D> position,
             final Matcher<? super Vector3D> velocity) {
         return new TypeSafeDiagnosingMatcher<PVCoordinates>() {
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("position ");
                 description.appendDescriptionOf(position);
                 description.appendText(" and velocity ");
                 description.appendDescriptionOf(velocity);
             }
 
             @Override
             protected boolean matchesSafely(PVCoordinates item,
                     Description mismatchDescription) {
                 if (!position.matches(item.getPosition())) {
                     // position doesn't match
                     mismatchDescription.appendText("position ");
                     position.describeMismatch(item.getPosition(), mismatchDescription);
                     return false;
                 } else if (!velocity.matches(item.getVelocity())) {
                     // velocity doesn't match
                     mismatchDescription.appendText("velocity ");
                     velocity.describeMismatch(item.getVelocity(), mismatchDescription);
                     return false;
                 } else {
                     // both p and v matched
                     return true;
                 }
             }
         };
     }
 
     /**
      * Check that a {@link PVCoordinates} is the same as another one.
      *
      * @param pv the reference {@link PVCoordinates}
      * @return a {@link PVCoordinates} {@link Matcher}
      */
     public static Matcher<PVCoordinates> pvIs(PVCoordinates pv) {
         return pvCloseTo(pv, 0);
     }
 
     /**
      * Match a {@link PVCoordinates} close to another one.
      *
      * @param pv     the reference {@link PVCoordinates}
      * @param absTol distance a matched {@link PVCoordinates} can be from the reference in
      *               any one coordinate.
      * @return a matcher of {@link PVCoordinates}.
      */
     public static Matcher<PVCoordinates> pvCloseTo(PVCoordinates pv,
                                                    double absTol) {
         return pvIs(vectorCloseTo(pv.getPosition(), absTol),
                 vectorCloseTo(pv.getVelocity(), absTol));
     }
 
     /**
      * Match a {@link PVCoordinates} close to another one.
      *
      * @param pv   the reference {@link PVCoordinates}
      * @param ulps the units in last place any coordinate can be off by.
      * @return a matcher of {@link PVCoordinates}.
      */
     public static Matcher<PVCoordinates> pvCloseTo(PVCoordinates pv, int ulps) {
         return pvIs(vectorCloseTo(pv.getPosition(), ulps),
                 vectorCloseTo(pv.getVelocity(), ulps));
     }
 
     /**
      * Checks if two numbers are relatively close to each other. For absolute
      * comparisons, see {@link #closeTo(double, double)}.
      *
      * @param expected the expected value in the relative comparison
      * @param ulps     the units in last place of {@code expected} the two
      *                 numbers can be off by.
      * @return a matcher of numbers
      */
     public static Matcher<Double> relativelyCloseTo(final double expected,
                                                     final int ulps) {
         return new TypeSafeDiagnosingMatcher<Double>() {
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("a numeric value within ")
                         .appendValue(ulps).appendText(" ulps of ")
                         .appendValue(expected);
             }
 
             @Override
             protected boolean matchesSafely(Double item,
                                             Description mismatchDescription) {
                 if (!Precision.equals(item, expected, ulps)) {
                     mismatchDescription
                             .appendValue(item)
                             .appendText(" was off by ")
                             .appendValue(
                                     Double.doubleToLongBits(item)
                                             - Double.doubleToLongBits(expected))
                             .appendText(" ulps");
                     return false;
                 }
                 return true;
             }
         };
     }
 
     /**
      * Check a number is close to another number using a relative
      * <strong>or</strong> absolute comparison.
      *
      * @param number the expected value
      * @param absTol absolute tolerance of comparison
      * @param ulps   units in last place tolerance for relative comparison
      * @return a matcher that matches if the differences is less than or equal
      * to absTol <strong>or</strong> the two numbers differ by less or equal
      * ulps.
      */
     public static Matcher<Double> numberCloseTo(double number, double absTol,
                                                 int ulps) {
         Collection<Matcher<Double>> matchers = new ArrayList<>(2);
         matchers.add(closeTo(number, absTol));
         matchers.add(relativelyCloseTo(number, ulps));
         return anyOf(matchers);
     }
 
     /**
      * Check a number is close to another number using a relative <strong>or</strong>
      * absolute comparison.
      *
      * @param expected the expected value
      * @param absTol   absolute tolerance of comparison
      * @param relTol   relative tolerance of {@code number}.
      * @return a matcher that matches if the differences is less than or equal to absTol
      * <strong>or</strong> the two numbers differ by less than the relative tolerance.
      */
     public static Matcher<Double> numberCloseTo(final double expected,
                                                 final double absTol,
                                                 final double relTol) {
         return new TypeSafeDiagnosingMatcher<Double>() {
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("a numeric value within ")
                         .appendValue(absTol).appendText(" absolute tolerance or")
                         .appendValue(relTol).appendText(" relative tolerance of ")
                         .appendValue(expected);
             }
 
             @Override
             protected boolean matchesSafely(Double item,
                                             Description mismatchDescription) {
                 final double tol = FastMath.max(absTol, relTol * FastMath.abs(expected));
                 final double difference = item - expected;
                 if (FastMath.abs(difference) > tol || Double.isNaN(item)
                         || Double.isNaN(expected)) {
                     mismatchDescription
                             .appendValue(item)
                             .appendText(" was off by ")
                             .appendValue(difference)
                             .appendText(" absolute and ")
                             .appendValue(difference / FastMath.abs(expected))
                             .appendText(" relative");
                     return false;
                 }
                 return true;
             }
         };
     }
 
     /**
      * match a double array based on matchers for each element.
      *
      * @param matchers matcher for each element.
      * @return a matcher for a double[]
      * @see org.hamcrest.collection.IsArray
      */
     @SafeVarargs
     public static Matcher<double[]> doubleArrayContaining(
             Matcher<? super Double>... matchers) {
         return new TypeSafeDiagnosingMatcher<double[]>() {
 
             @Override
             public void describeTo(Description description) {
                 description.appendList("[", ", ", "]", Arrays.<Matcher<?>>asList(matchers));
             }
 
             @Override
             protected boolean matchesSafely(double[] actual,
                                             Description mismatchDescription) {
                 if (actual.length != matchers.length) {
                     mismatchDescription.appendText("array length was " + actual.length);
                     return false;
                 }
                 for (int i = 0; i < actual.length; i++) {
                     if (!matchers[i].matches(actual[i])) {
                         mismatchDescription.appendText("in element " + i + " ");
                         matchers[i].describeMismatch(actual[i],
                                 mismatchDescription);
                         return false;
                     }
                 }
                 return true;
             }
         };
     }
 
     /**
      * Check that the double[] contains exactly the specified values.
      *
      * @param values the expected values.
      * @return matcher for double[]s
      * @see Matchers#arrayContaining(Object...)
      */
     public static Matcher<double[]> doubleArrayContaining(double... values) {
         @SuppressWarnings("unchecked")
         Matcher<Double>[] elementMatchers = new Matcher[values.length];
         for (int i = 0; i < elementMatchers.length; i++) {
             elementMatchers[i] = Matchers.is(values[i]);
         }
         return doubleArrayContaining(elementMatchers);
     }
 
     /**
      * Check that a double[] contains the specified values to within an absolute
      * tolerance.
      *
      * @param values the expected values
      * @param absTol the absolute tolerance used in comparisons
      * @return a {@link Matcher} for double[]'s
      */
     public static Matcher<double[]> doubleArrayContaining(
             final double[] values, final double absTol) {
         @SuppressWarnings("unchecked")
         Matcher<Double>[] elementMatchers = new Matcher[values.length];
         for (int i = 0; i < elementMatchers.length; i++) {
             elementMatchers[i] = closeTo(values[i], absTol);
         }
         return doubleArrayContaining(elementMatchers);
     }
 
     /**
      * Check that a double[] contains the specified values to within a relative
      * tolerance.
      *
      * @param values the expected values
      * @param ulps   the units in last place the values can be off by. These are ulps of
      *               the expected values. Specifying 1 ulp corresponds to ~16 decimal
      *               digits of accuracy.
      * @return a {@link Matcher} for a double[]
      */
     public static Matcher<double[]> doubleArrayContaining(
             final double[] values, final int ulps) {
         @SuppressWarnings("unchecked")
         Matcher<Double>[] elementMatchers = new Matcher[values.length];
         for (int i = 0; i < elementMatchers.length; i++) {
             elementMatchers[i] = relativelyCloseTo(values[i], ulps);
         }
         return doubleArrayContaining(elementMatchers);
     }
 
     /**
      * Check that a double[] contains the specified values to within a relative tolerance
      * or absolute tolerance. Specifically, each comparison will pass if the difference is
      * less than {@code absTol} <em>Or</em> the difference, expressed in ulps is less than
      * {@code ulps}.
      *
      * @param values the expected values
      * @param absTol absolute tolerance on comparisons
      * @param ulps   relative tolerance, in units in last place
      * @return matcher for the double array
      */
     public static Matcher<double[]> doubleArrayContaining(
             final double[] values, final double absTol, final int ulps) {
         @SuppressWarnings("unchecked")
         Matcher<Double>[] elementMatchers = new Matcher[values.length];
         for (int i = 0; i < elementMatchers.length; i++) {
             elementMatchers[i] = numberCloseTo(values[i], absTol, ulps);
         }
         return doubleArrayContaining(elementMatchers);
     }
 
     /**
      * Match a {@link RealMatrix#getData()} as a double[][].
      *
      * @param dataMatcher matcher for the data as a double[][]
      * @return a {@link RealMatrix} matcher
      */
     public static Matcher<RealMatrix> matrix(
             final Matcher<double[][]> dataMatcher) {
         return new TypeSafeDiagnosingMatcher<RealMatrix>() {
             @Override
             public void describeTo(Description description) {
                 description.appendText("matrix that ").appendDescriptionOf(
                         dataMatcher);
             }
 
             @Override
             protected boolean matchesSafely(RealMatrix item,
                                             Description mismatchDescription) {
                 if (dataMatcher.matches(item.getData())) {
                     return true;
                 } else {
                     mismatchDescription.appendText("matrix did not match ");
                     dataMatcher.describeMismatch(item.getData(),
                             mismatchDescription);
                     return false;
                 }
             }
         };
     }
 
     /**
      * Match a {@link RealMatrix} to within the given absolute tolerance
      *
      * @param expected the expected values
      * @param absTol   the absolute tolerance on the comparison
      * @return a matrix matcher
      * @see #matrix(Matcher)
      * @see #doubleArrayContaining(double[], double)
      */
     public static Matcher<RealMatrix> matrixCloseTo(RealMatrix expected,
                                                     double absTol) {
         @SuppressWarnings("rawtypes")
         Matcher[] rowMatchers = new Matcher[expected.getRowDimension()];
         for (int i = 0; i < rowMatchers.length; i++) {
             rowMatchers[i] = doubleArrayContaining(expected.getRow(i), absTol);
         }
         @SuppressWarnings("unchecked")
         Matcher<double[][]> dataMatcher = array(rowMatchers);
         return matrix(dataMatcher);
     }
 
     /**
      * Match a {@link RealMatrix} to within the given absolute tolerance
      *
      * @param expected the expected values
      * @param absTol   the absolute tolerance on the comparison
      * @param ulps     the maximum allowable difference, in units in last place
      * @return a matrix matcher
      * @see #matrix(Matcher)
      * @see #doubleArrayContaining(double[], double)
      */
     public static Matcher<RealMatrix> matrixCloseTo(RealMatrix expected,
                                                     double absTol, int ulps) {
         @SuppressWarnings("rawtypes")
         Matcher[] rowMatchers = new Matcher[expected.getRowDimension()];
         for (int i = 0; i < rowMatchers.length; i++) {
             rowMatchers[i] = doubleArrayContaining(expected.getRow(i), absTol,
                     ulps);
         }
         @SuppressWarnings("unchecked")
         Matcher<double[][]> dataMatcher = array(rowMatchers);
         return matrix(dataMatcher);
     }
 
     /**
      * Create a matcher that matches if at least one of the given matchers match. Gives
      * better descriptions that {@link org.hamcrest.CoreMatchers#anyOf(Iterable)}.
      *
      * @param matchers to try.
      * @param <T>      type of object to match.
      * @return a new matcher.
      */
     public static <T> Matcher<T> anyOf(Collection<? extends Matcher<? super T>> matchers) {
         return new TypeSafeDiagnosingMatcher<T>() {
             @Override
             protected boolean matchesSafely(final T item,
                                             final Description mismatchDescription) {
                 boolean first = true;
                 for (Matcher<? super T> matcher : matchers) {
                     if (matcher.matches(item)) {
                         return true;
                     } else {
                         if (!first) {
                             mismatchDescription.appendText(" and ");
                         }
                         matcher.describeMismatch(item, mismatchDescription);
                     }
                     first = false;
                 }
                 return false;
             }
 
             @Override
             public void describeTo(final Description description) {
                 description.appendList("(", " or ", ")", matchers);
             }
         };
     }
 
     /* Copid from Hamcrest's IsCloseTo under the new BSD license.
      * Copyright (c) 2000-2006 hamcrest.org
      */
 
     /**
      * Creates a matcher of {@link Double}s that matches when an examined double
      * is equal to the specified <code>operand</code>, within a range of +/-
      * <code>error</code>. <p/> For example:
      * <pre>assertThat(1.03, is(closeTo(1.0, 0.03)))</pre>
      *
      * @param value the expected value of matching doubles
      * @param delta the delta (+/-) within which matches will be allowed
      * @return a double matcher.
      */
     public static Matcher<Double> closeTo(final double value,
                                           final double delta) {
 
         return new TypeSafeMatcher<Double>() {
             @Override
             public boolean matchesSafely(Double item) {
                 return actualDelta(item) <= 0.0;
             }
 
             @Override
             public void describeMismatchSafely(Double item, Description mismatchDescription) {
                 mismatchDescription.appendValue(item)
                         .appendText(" differed by ")
                         .appendValue(actualDelta(item));
             }
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("a numeric value within ")
                         .appendValue(delta)
                         .appendText(" of ")
                         .appendValue(value);
             }
 
             private double actualDelta(Double item) {
                 return (FastMath.abs((item - value)) - delta);
             }
         };
 
     }
 
     /**
      * Creates a matcher of {@link Double}s that matches when an examined double
      * is equal to the specified <code>operand</code>, within a range of +/-
      * <code>error</code>. <p/> For example:
      * <pre>assertThat(1.03, is(closeTo(1.0, 0.03)))</pre>
      *
      * @param value the expected value of matching doubles
      * @param delta the delta (+/-) within which matches will be allowed
      * @return a double matcher.
      */
     public static <T extends CalculusFieldElement<T>> Matcher<T> closeTo(
             final T value,
             final double delta) {
 
         return new TypeSafeMatcher<T>() {
             @Override
             public boolean matchesSafely(T item) {
                 // actualDelta(item) <= 0.0
                 return actualDelta(item).sign().getReal() <= 0.0;
             }
 
             @Override
             public void describeMismatchSafely(T item, Description mismatchDescription) {
                 mismatchDescription.appendValue(item)
                         .appendText(" differed by ")
                         .appendValue(actualDelta(item));
             }
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("a numeric value within ")
                         .appendValue(delta)
                         .appendText(" of ")
                         .appendValue(value);
             }
 
             private T actualDelta(T item) {
                 return item.subtract(value).abs().subtract(delta);
             }
         };
 
     }
 
     /* Replace with Matchers.greaterThan(...) if hamcrest becomes available. */
 
     /**
      * Create a matcher to see if a value is greater than another one using {@link
      * Comparable#compareTo(Object)}.
      *
      * @param expected value.
      * @param <T>      type of value.
      * @return matcher of value.
      */
     public static <T extends Comparable<T>> Matcher<T> greaterThan(final T expected) {
         return new TypeSafeDiagnosingMatcher<T>() {
             @Override
             protected boolean matchesSafely(T item, Description mismatchDescription) {
                 if (expected.compareTo(item) >= 0) {
                     mismatchDescription.appendText("less than or equal to ")
                             .appendValue(expected);
                     return false;
                 }
                 return true;
             }
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("greater than ").appendValue(expected);
             }
         };
     }
 
 
     /**
      * Matcher for the distance in seconds between two {@link AbsoluteDate}s. Uses {@link
      * AbsoluteDate#durationFrom(AbsoluteDate)}.
      *
      * @param date         the date to compare with.
      * @param valueMatcher the matcher for the delta. For example, {@code closeTo(0,
      *                     1e-10)}.
      * @return a matcher that checks the time difference between two {@link
      * AbsoluteDate}s.
      */
     public static Matcher<AbsoluteDate> durationFrom(final AbsoluteDate date,
                                                      final Matcher<Double> valueMatcher) {
         return new TypeSafeDiagnosingMatcher<AbsoluteDate>() {
             @Override
             public void describeTo(Description description) {
                 description.appendText("delta from ");
                 description.appendValue(date);
                 description.appendText(" is ");
                 description.appendDescriptionOf(valueMatcher);
             }
 
             @Override
             protected boolean matchesSafely(AbsoluteDate item,
                                             Description mismatchDescription) {
                 double delta = item.durationFrom(date);
                 boolean matched = valueMatcher.matches(delta);
                 if (!matched) {
                     mismatchDescription.appendText("delta to ");
                     mismatchDescription.appendValue(item);
                     mismatchDescription.appendText(" ");
                     valueMatcher.describeMismatch(delta, mismatchDescription);
                 }
                 return matched;
             }
         };
     }
 
     /**
      * Matcher that compares to {@link Rotation}s using {@link Rotation#distance(Rotation,
      * Rotation)}.
      *
      * @param from         one of the rotations to compare
      * @param valueMatcher matcher for the distances. For example {@code closeTo(0,
      *                     1e-10)}.
      * @return a matcher for rotations.
      */
     public static Matcher<Rotation> distanceIs(final Rotation from,
                                                final Matcher<Double> valueMatcher) {
         return new TypeSafeDiagnosingMatcher<Rotation>() {
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("distance from ");
                 description.appendValue(from);
                 description.appendText(" is ");
                 description.appendDescriptionOf(valueMatcher);
             }
 
             @Override
             protected boolean matchesSafely(Rotation item,
                                             Description mismatchDescription) {
                 double distance = Rotation.distance(from, item);
                 boolean matched = valueMatcher.matches(distance);
                 if (!matched) {
                     mismatchDescription.appendText("distance to ");
                     mismatchDescription.appendValue(item);
                     mismatchDescription.appendText(" was ");
                     valueMatcher
                             .describeMismatch(distance, mismatchDescription);
                 }
                 return matched;
             }
         };
     }
 
     /**
      * Check that two attitudes are equivalent.
      *
      * @param expected attitude.
      * @return attitude matcher.
      */
     public static Matcher<Attitude> attitudeIs(final Attitude expected) {
         final Matcher<AbsoluteDate> dateMatcher = durationFrom(expected.getDate(), is(0.0));
         final Matcher<Rotation> rotationMatcher = distanceIs(expected.getRotation(), is(0.0));
         final Matcher<Vector3D> spinMatcher = vectorCloseTo(expected.getSpin(), 0);
         final Matcher<Vector3D> accelerationMatcher =
                 vectorCloseTo(expected.getRotationAcceleration(), 0);
         final Rotation r = expected.getRotation();
         return new TypeSafeDiagnosingMatcher<Attitude>() {
 
             @Override
             protected boolean matchesSafely(Attitude item,
                                             final Description mismatchDescription) {
                 item = item.withReferenceFrame(expected.getReferenceFrame());
                 if (!dateMatcher.matches(item)) {
                     mismatchDescription.appendText("date ")
                             .appendDescriptionOf(dateMatcher);
                 }
                 if (!rotationMatcher.matches(item.getRotation())) {
                     mismatchDescription.appendText("rotation ")
                             .appendDescriptionOf(rotationMatcher);
                     return false;
                 }
                 if (!spinMatcher.matches(item.getSpin())) {
                     mismatchDescription.appendText("spin ")
                             .appendDescriptionOf(spinMatcher);
                     return false;
                 }
                 if (!accelerationMatcher.matches(item.getRotationAcceleration())) {
                     mismatchDescription.appendText("rotation acceleration ")
                             .appendDescriptionOf(accelerationMatcher);
                     return false;
                 }
                 return true;
             }
 
             @Override
             public void describeTo(Description description) {
                 description.appendText("attitude on ").appendValue(expected.getDate())
                         .appendText(" rotation ").appendValueList("[", ",", "]", r.getQ0(), r.getQ1(), r.getQ2(), r.getQ3())
                         .appendText(" spin ").appendDescriptionOf(spinMatcher)
                         .appendText(" acceleration ").appendDescriptionOf(accelerationMatcher);
             }
         };
     }
 
 
 }