/* Copyright 2002-2026 CS GROUP
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    * 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,
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   * See the License for the specific language governing permissions and
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  package org.orekit.estimation.measurements.gnss;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.stream.Collectors;
  
  import org.hipparchus.linear.MatrixUtils;
  import org.hipparchus.linear.QRDecomposer;
  import org.hipparchus.linear.RealMatrix;
  import org.hipparchus.linear.RealVector;
  import org.hipparchus.util.FastMath;
  import org.orekit.errors.OrekitIllegalArgumentException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.utils.drivers.ParameterDriver;
  
  /** Class for solving integer ambiguity problems.
   * @see LambdaMethod
   * @author Luc Maisonobe
   * @since 10.0
   */
  public class AmbiguitySolver {
  
      /** Drivers for ambiguity drivers. */
      private final List<ParameterDriver> ambiguityDrivers;
  
      /** Solver for the underlying Integer Least Square problem. */
      private final IntegerLeastSquareSolver solver;
  
      /** Acceptance test to use. */
      private final AmbiguityAcceptance acceptance;
  
      /** Simple constructor.
       * @param ambiguityDrivers drivers for ambiguity parameters
       * @param solver solver for the underlying Integer Least Square problem
       * @param acceptance acceptance test to use
       * @see LambdaMethod
       */
      public AmbiguitySolver(final List<ParameterDriver> ambiguityDrivers,
                             final IntegerLeastSquareSolver solver,
                             final AmbiguityAcceptance acceptance) {
          this.ambiguityDrivers = ambiguityDrivers;
          this.solver           = solver;
          this.acceptance       = acceptance;
      }
  
      /** Get all the ambiguity parameters drivers.
       * @return all ambiguity parameters drivers
       */
      public List<ParameterDriver> getAllAmbiguityDrivers() {
          return Collections.unmodifiableList(ambiguityDrivers);
      }
  
      /** Get the ambiguity parameters drivers that have not been fixed yet.
       * @return ambiguity parameters drivers that have not been fixed yet
       */
      protected List<ParameterDriver> getFreeAmbiguityDrivers() {
          return ambiguityDrivers.
                          stream().
                          filter(d -> {
                              if (d.isSelected()) {
                                  // in order to make the code generic and compatible with pDriver having
                                  // 1 or several values driven getValue is called with a "random date"
                                  // it should be OK as we take the near number
                                  final double near   = FastMath.rint(d.getValue());
                                  final double gapMin = near - d.getMinValue();
                                  final double gapMax = d.getMaxValue() - near;
                                  return FastMath.max(FastMath.abs(gapMin), FastMath.abs(gapMax)) > 1.0e-15;
                              } else {
                                  return false;
                              }
                          }).
                          collect(Collectors.toList());
      }
  
      /** Get ambiguity indirection array for ambiguity parameters drivers that have not been fixed yet.
       * @param startIndex start index for measurements parameters in global covariance matrix
       * @param measurementsParametersDrivers measurements parameters drivers in global covariance matrix order
       * @return indirection array between full covariance matrix and ambiguity covariance matrix
       */
      protected int[] getFreeAmbiguityIndirection(final int startIndex,
                                                  final List<ParameterDriver> measurementsParametersDrivers) {
  
         // set up indirection array
         final List<ParameterDriver> freeDrivers = getFreeAmbiguityDrivers();
         final List<String> measurementsPDriversNames = new ArrayList<>();
         final int totalValuesToEstimate = freeDrivers.size();
         for (ParameterDriver measDriver : measurementsParametersDrivers) {
             measurementsPDriversNames.add(measDriver.getName());
         }
 
         final int[] indirection = new int[totalValuesToEstimate];
         int nb = 0;
         for (ParameterDriver freeDriver : freeDrivers) {
 
             indirection[nb] = -1;
 
             for (int k = 0; k < measurementsPDriversNames.size(); ++k) {
                 if (freeDriver.getName().equals(measurementsPDriversNames.get(k))) {
                     indirection[nb] = startIndex + k;
                     break;
                 }
             }
 
             if (indirection[nb] < 0) {
                 // the parameter was not found
                 final StringBuilder builder = new StringBuilder();
                 for (final String driverName : measurementsPDriversNames) {
                     if (!builder.isEmpty()) {
                         builder.append(", ");
                     }
                     builder.append(driverName);
                 }
                 throw new OrekitIllegalArgumentException(OrekitMessages.UNSUPPORTED_PARAMETER_NAME,
                                                          freeDriver.getName(), builder.toString());
             }
             nb++;
         }
 
         return indirection;
 
     }
 
     /** Un-fix an integer ambiguity (typically after a phase cycle slip).
      * @param ambiguityDriver driver for the ambiguity to un-fix
      */
     public void unFixAmbiguity(final ParameterDriver ambiguityDriver) {
         ambiguityDriver.setMinValue(Double.NEGATIVE_INFINITY);
         ambiguityDriver.setMaxValue(Double.POSITIVE_INFINITY);
     }
 
     /** Fix integer ambiguities.
      * @param startIndex start index for measurements parameters in global covariance matrix
      * @param measurementsParametersDrivers measurements parameters drivers in global covariance matrix order
      * @param covariance global covariance matrix
      * @return list of newly fixed ambiguities (ambiguities already fixed before the call are not counted)
      */
     public List<ParameterDriver> fixIntegerAmbiguities(final int startIndex,
                                                        final List<ParameterDriver> measurementsParametersDrivers,
                                                        final RealMatrix covariance) {
 
         // set up Integer Least Square problem
         final List<ParameterDriver> ambiguities      = getAllAmbiguityDrivers();
 
         // construct float ambiguities array
         final double[] floatAmbiguities = new double[ambiguities.size()];
         int floatAmbRank = 0;
         for (ParameterDriver pDriver : ambiguities) {
             floatAmbiguities[floatAmbRank++] = pDriver.getValue();
         }
 
         final int[]                 indirection      = getFreeAmbiguityIndirection(startIndex, measurementsParametersDrivers);
         // solve the ILS problem
         final IntegerLeastSquareSolution[] candidates =
                         solver.solveILS(acceptance.numberOfCandidates(), floatAmbiguities, indirection, covariance);
 
         // FIXME A cleaner way is:
         //     1°/ Add a getName() method in IntegerLeastSquareSolver interface
         //     2°/ Add static name attribute to IntegerBootstrapping, LAMBDA and ModifiedLAMBDA classes
         if (solver instanceof IntegerBootstrapping && candidates.length == 0) {
             return Collections.emptyList();
         }
 
         // check number of candidates
         if (candidates.length < acceptance.numberOfCandidates()) {
             return Collections.emptyList();
         }
 
         // check acceptance
         final IntegerLeastSquareSolution bestCandidate = acceptance.accept(candidates);
         if (bestCandidate == null) {
             return Collections.emptyList();
         }
 
         // fix the ambiguities
         final long[] fixedAmbiguities = bestCandidate.getSolution();
         final List<ParameterDriver> fixedDrivers = new ArrayList<>(indirection.length);
         final int nb = measurementsParametersDrivers.size();
         for (int i = 0; i < nb; ++i) {
             final ParameterDriver driver = measurementsParametersDrivers.get(indirection[i] - startIndex);
             driver.setMinValue(fixedAmbiguities[i]);
             driver.setMaxValue(fixedAmbiguities[i]);
             fixedDrivers.add(driver);
         }
 
         // Update the others parameter drivers accordingly to the fixed integer ambiguity
         // Covariance matrix between integer ambiguity and the other parameter driver
         final RealMatrix Qab = getCovMatrix(covariance, indirection);
 
         final RealVector X = new QRDecomposer(1.0e-10).decompose(getAmbiguityMatrix(covariance, indirection)).solve(MatrixUtils.createRealVector(floatAmbiguities).
                                                                                                            subtract(MatrixUtils.createRealVector(toDoubleArray(fixedAmbiguities.length, fixedAmbiguities))));
         final RealVector Y =  Qab.preMultiply(X);
 
         int entry = 0;
         for (int i = startIndex + 1; i < covariance.getColumnDimension(); i++) {
             if (!belongTo(indirection, i)) {
                 final ParameterDriver driver = measurementsParametersDrivers.get(i - startIndex);
                 driver.setValue(driver.getValue() - Y.getEntry(entry++ - startIndex));
             }
         }
 
         return fixedDrivers;
 
     }
 
    /** Get the covariance matrix between the integer ambiguities and the other parameter driver.
     * @param cov global covariance matrix
     * @param indirection array of the position of integer ambiguity parameter driver
     * @return covariance matrix.
     */
     private RealMatrix getCovMatrix(final RealMatrix cov, final int[] indirection) {
         final RealMatrix Qab = MatrixUtils.createRealMatrix(indirection.length, cov.getColumnDimension());
         int index = 0;
         int iter  = 0;
         while (iter < indirection.length) {
             // Loop on column dimension
             for (int j = 0; j < cov.getColumnDimension(); j++) {
                 if (!belongTo(indirection, j)) {
                     Qab.setEntry(index, 0, cov.getEntry(index, 0));
                 }
             }
             index++;
             iter++;
         }
         return Qab;
     }
 
      /** Return the matrix of the ambiguity from the global covariance matrix.
       * @param cov global covariance matrix
       * @param indirection array of the position of the ambiguity within the global covariance matrix
       * @return matrix of ambiguities covariance
       */
     private RealMatrix getAmbiguityMatrix(final RealMatrix cov, final int[] indirection) {
         final RealMatrix Qa = MatrixUtils.createRealMatrix(indirection.length, indirection.length);
         for (int i = 0; i < indirection.length; i++) {
             Qa.setEntry(i, i, cov.getEntry(indirection[i], indirection[i]));
             for (int j = 0; j < i; j++) {
                 Qa.setEntry(i, j, cov.getEntry(indirection[i], indirection[j]));
                 Qa.setEntry(j, i, cov.getEntry(indirection[i], indirection[j]));
             }
         }
         return Qa;
     }
 
     /** Compute whether or not the integer pos belongs to the indirection array.
      * @param indirection array of the position of ambiguities within the global covariance matrix
      * @param pos integer for which we want to know if it belong to the indirection array.
      * @return true if it belongs.
      */
     private boolean belongTo(final int[] indirection, final int pos) {
         for (int j : indirection) {
             if (pos == j) {
                 return true;
             }
         }
         return false;
     }
 
     /** Transform an array of long to an array of double.
      * @param size size of the destination array
      * @param longArray source array
      * @return the destination array
      */
     private double[] toDoubleArray(final int size, final long[] longArray) {
         // Initialize double array
         final double[] doubleArray = new double[size];
         // Copy the elements
         for (int index = 0; index < size; index++) {
             doubleArray[index] = longArray[index];
         }
         return doubleArray;
     }
 
 }