/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed 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.txt
 *
 *  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.
 *
 *=========================================================================*/

#include <set>
#include "itkRegularStepGradientDescentOptimizer.h"
#include "itkMath.h"

/**
 *  The objectif function is the quadratic form:
 *
 *  1/2 x^T A x - b^T x
 *
 *  Where A is a matrix and b is a vector
 *  The system in this example is:
 *
 *     | 3  2 ||x|   | 2|   |0|
 *     | 2  6 ||y| + |-8| = |0|
 *
 *
 *   the solution is the vector | 2 -2 |
 *
 * \class RSGCostFunction
 */
class RSGCostFunction : public itk::SingleValuedCostFunction
{
public:
  using Self = RSGCostFunction;
  using Superclass = itk::SingleValuedCostFunction;
  using Pointer = itk::SmartPointer<Self>;
  using ConstPointer = itk::SmartPointer<const Self>;
  itkNewMacro(Self);

  enum
  {
    SpaceDimension = 2
  };

  using ParametersType = Superclass::ParametersType;
  using DerivativeType = Superclass::DerivativeType;
  using MeasureType = Superclass::MeasureType;


  RSGCostFunction() = default;


  MeasureType
  GetValue(const ParametersType & parameters) const override
  {

    double x = parameters[0];
    double y = parameters[1];

    std::cout << "GetValue( ";
    std::cout << x << " ";
    std::cout << y << ") = ";

    MeasureType measure = 0.5 * (3 * x * x + 4 * x * y + 6 * y * y) - 2 * x + 8 * y;

    std::cout << measure << std::endl;
    return measure;
  }

  void
  GetDerivative(const ParametersType & parameters, DerivativeType & derivative) const override
  {

    double x = parameters[0];
    double y = parameters[1];

    std::cout << "GetDerivative( ";
    std::cout << x << " ";
    std::cout << y << ") = ";

    derivative = DerivativeType(SpaceDimension);
    derivative[0] = 3 * x + 2 * y - 2;
    derivative[1] = 2 * x + 6 * y + 8;
  }


  unsigned int
  GetNumberOfParameters() const override
  {
    return SpaceDimension;
  }

private:
};

int
itkRegularStepGradientDescentOptimizerTest(int, char *[])
{
  std::cout << "RegularStepGradientDescentOptimizer Test ";
  std::cout << std::endl << std::endl;

  using OptimizerType = itk::RegularStepGradientDescentOptimizer;

  using ScalesType = OptimizerType::ScalesType;


  // Declaration of a itkOptimizer
  OptimizerType::Pointer itkOptimizer = OptimizerType::New();


  // Declaration of the CostFunction
  RSGCostFunction::Pointer costFunction = RSGCostFunction::New();


  itkOptimizer->SetCostFunction(costFunction);


  using ParametersType = RSGCostFunction::ParametersType;


  const unsigned int spaceDimension = costFunction->GetNumberOfParameters();

  // We start not so far from  | 2 -2 |
  ParametersType initialPosition(spaceDimension);
  initialPosition[0] = 100;
  initialPosition[1] = -100;

  ScalesType parametersScale(spaceDimension);
  parametersScale[0] = 1.0;
  parametersScale[1] = 1.0;

  itkOptimizer->MinimizeOn();
  itkOptimizer->SetScales(parametersScale);
  itkOptimizer->SetGradientMagnitudeTolerance(1e-6);
  itkOptimizer->SetMaximumStepLength(30.0);
  itkOptimizer->SetMinimumStepLength(1e-6);
  itkOptimizer->SetNumberOfIterations(900);

  itkOptimizer->SetInitialPosition(initialPosition);

  try
  {
    itkOptimizer->StartOptimization();
  }
  catch (const itk::ExceptionObject & e)
  {
    std::cout << "Exception thrown ! " << std::endl;
    std::cout << "An error occurred during Optimization" << std::endl;
    std::cout << "Location    = " << e.GetLocation() << std::endl;
    std::cout << "Description = " << e.GetDescription() << std::endl;
    return EXIT_FAILURE;
  }


  ParametersType finalPosition = itkOptimizer->GetCurrentPosition();
  std::cout << "Solution        = (";
  std::cout << finalPosition[0] << ",";
  std::cout << finalPosition[1] << ")" << std::endl;

  //
  // check results to see if it is within range
  //
  bool   pass = true;
  double trueParameters[2] = { 2, -2 };
  for (unsigned int j = 0; j < 2; j++)
  {
    if (itk::Math::abs(finalPosition[j] - trueParameters[j]) > 0.01)
    {
      pass = false;
    }
  }

  if (!pass)
  {
    std::cout << "Test failed." << std::endl;
    return EXIT_FAILURE;
  }


  // Run now with a different relaxation factor

  {
    itkOptimizer->SetInitialPosition(initialPosition);

    itkOptimizer->SetRelaxationFactor(0.8);
    try
    {
      itkOptimizer->StartOptimization();
    }
    catch (const itk::ExceptionObject & e)
    {
      std::cout << "Exception thrown ! " << std::endl;
      std::cout << "An error occurred during Optimization" << std::endl;
      std::cout << "Location    = " << e.GetLocation() << std::endl;
      std::cout << "Description = " << e.GetDescription() << std::endl;
      return EXIT_FAILURE;
    }

    finalPosition = itkOptimizer->GetCurrentPosition();
    std::cout << "Solution        = (";
    std::cout << finalPosition[0] << ",";
    std::cout << finalPosition[1] << ")" << std::endl;

    //
    // check results to see if it is within range
    //
    pass = true;
    for (unsigned int j = 0; j < 2; j++)
    {
      if (itk::Math::abs(finalPosition[j] - trueParameters[j]) > 0.01)
      {
        pass = false;
      }
    }

    if (!pass)
    {
      std::cout << "Test failed." << std::endl;
      return EXIT_FAILURE;
    }
  }

  //
  // Verify that the optimizer doesn't run if the
  // number of iterations is set to zero.
  //
  {
    itkOptimizer->SetNumberOfIterations(0);
    itkOptimizer->SetInitialPosition(initialPosition);

    try
    {
      itkOptimizer->StartOptimization();
    }
    catch (const itk::ExceptionObject & excp)
    {
      std::cout << excp << std::endl;
      return EXIT_FAILURE;
    }

    if (itkOptimizer->GetCurrentIteration() > 0)
    {
      std::cerr << "The optimizer is running iterations despite of ";
      std::cerr << "having a maximum number of iterations set to zero" << std::endl;
      return EXIT_FAILURE;
    }
  }

  //
  // Test the Exception if the GradientMagnitudeTolerance is set to a negative value
  //
  itkOptimizer->SetGradientMagnitudeTolerance(-1.0);
  bool expectedExceptionReceived = false;
  try
  {
    itkOptimizer->StartOptimization();
  }
  catch (const itk::ExceptionObject & excp)
  {
    expectedExceptionReceived = true;
    std::cout << "Expected Exception " << std::endl;
    std::cout << excp << std::endl;
  }

  if (!expectedExceptionReceived)
  {
    std::cerr << "Failure to produce an exception when";
    std::cerr << "the GradientMagnitudeTolerance is negative " << std::endl;
    std::cerr << "TEST FAILED !" << std::endl;
    return EXIT_FAILURE;
  }

  // Test streaming enumeration for
  // RegularStepGradientDescentBaseOptimizerEnums::StopCondition elements
  const std::set<itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition> allStopCondition{
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::GradientMagnitudeTolerance,
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::StepTooSmall,
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::ImageNotAvailable,
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::CostFunctionError,
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::MaximumNumberOfIterations,
    itk::RegularStepGradientDescentBaseOptimizerEnums::StopCondition::Unknown
  };
  for (const auto & ee : allStopCondition)
  {
    std::cout << "STREAMED ENUM VALUE "
                 "RegularStepGradientDescentBaseOptimizerEnums::StopCondition: "
              << ee << std::endl;
  }

  std::cout << "TEST PASSED !" << std::endl;
  return EXIT_SUCCESS;
}