/*=========================================================================
 *
 *  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
 *
 *         https://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.
 *
 *=========================================================================*/
#ifndef itkHilbertPath_h
#define itkHilbertPath_h

#include "itkPath.h"

#include "itkNumericTraits.h"

namespace itk
{
/**
 * \class HilbertPath
 * \brief  Represent an n-dimensional Hilbert path for a given order
 *
 * This class is used to construct a Hilbert spacing-filling curve
 * (or path) for a given order and given dimension.  The locality-
 * preserving properties make the Hilbert path an attractive option
 * for mapping multi-dimensional data to a single array.
 *
 * The path is defined by its dimensionality and order( >= 1 ) with its
 * starting point at [0]^Dimension. The size of the path in each dimension
 * is 2^order where each discrete location is visited by that path.
 * For example, a 2-D Hilbert path of order 8 can map each pixel of a 256x256
 * image onto a single array.  More properties and visualizations can be
 * found in various places on the web.
 *
 * The implementation is based on
 * Chris Hamilton, "Compact Hilbert Indices", Technical Report CS-2006-07,
 * July 24, 2006.
 * and a direct porting of the Aldo Cortesi's python code found at
 * https://github.com/cortesi/scurve
 *
 * \author Nick Tustison
 *
 * \ingroup ITKPath
 */
template <typename TIndexValue = unsigned int, unsigned int VDimension = 3>
class ITK_TEMPLATE_EXPORT HilbertPath : public Path<TIndexValue, Index<VDimension>, VDimension>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(HilbertPath);

  /** Standard class type aliases. */
  using Self = HilbertPath<TIndexValue, VDimension>;
  using Superclass = Path<unsigned int, Index<VDimension>, VDimension>;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(HilbertPath);

  /** New() method for dynamic construction */
  itkNewMacro(Self);

  /** Dimension underlying input image. */
  static constexpr unsigned int Dimension = VDimension;

  /** OutputType type alias support */
  using typename Superclass::OutputType;
  using typename Superclass::InputType;

  /** The input/output type alias*/
  using PathIndexType = InputType;
  using IndexType = OutputType;
  using HilbertOrderType = unsigned int;
  using HilbertPathType = std::vector<IndexType>;
  using HilbertPathSizeType = typename HilbertPathType::size_type;
  using typename Superclass::OffsetType;

  // Functions inherited from Path

  /** Evaluate the hilbert path for the index at the specified path-position. */
  OutputType
  Evaluate(const PathIndexType & input) const override
  {
    return this->m_HilbertPath[input];
  }

  OutputType
  EvaluateToIndex(const PathIndexType & input) const override
  {
    return this->m_HilbertPath[input];
  }

  /** Evaluate the hilbert path for the path-position at the specified index. */
  virtual InputType
  EvaluateInverse(const IndexType & input)
  {
    return this->TransformMultiDimensionalIndexToPathIndex(input);
  }

  /** Where does the path end (what is the last valid input value)? */
  InputType
  EndOfInput() const override
  {
    return static_cast<InputType>(this->NumberOfSteps()); // 0 is before the first step, 1 is after it
  }

  /** Increment the input variable passed by reference and then return the
   * index stored at the new path-position.
   */
  OffsetType
  IncrementInput(InputType & itkNotUsed(input)) const override
  {
    itkExceptionMacro("Not implemented.");
  }

  /** Remove all steps from the path*/
  virtual inline void
  Clear()
  {
    this->m_HilbertPath.clear();
    this->Modified();
  }

  /** How many steps in the path? */
  virtual inline HilbertPathSizeType
  NumberOfSteps() const
  {
    return m_HilbertPath.size();
  }

  /** Needed for Pipelining */
  void
  Initialize() override
  {
    this->Clear();
    this->ConstructHilbertPath();
  }

  /**
   * Set/get Hilbert order.  The multi-dimensional space is of size 2^(HilbertOrder).
   */
  itkSetClampMacro(HilbertOrder, HilbertOrderType, 1, NumericTraits<HilbertOrderType>::max());
  itkGetConstMacro(HilbertOrder, HilbertOrderType);

  /** Convert the path index to the multidimensional index location */
  IndexType
  TransformPathIndexToMultiDimensionalIndex(const PathIndexType id);

  /** Convert the multidimensional index to the path index */
  PathIndexType
  TransformMultiDimensionalIndexToPathIndex(const IndexType & index);

protected:
  HilbertPath();
  ~HilbertPath() override = default;
  void
  PrintSelf(std::ostream & os, Indent indent) const override;

private:
  void
  ConstructHilbertPath();

  PathIndexType
  GetTransform(const PathIndexType, const PathIndexType, const PathIndexType, const PathIndexType);

  PathIndexType
  GetInverseTransform(const PathIndexType, const PathIndexType, const PathIndexType, const PathIndexType);

  PathIndexType
  GetGrayCode(const PathIndexType);

  PathIndexType
  GetInverseGrayCode(const PathIndexType);

  PathIndexType
  SetBit(const PathIndexType, const PathIndexType, const PathIndexType, const PathIndexType);

  PathIndexType
  GetRightBitRotation(PathIndexType, PathIndexType, const PathIndexType);

  PathIndexType
  GetLeftBitRotation(PathIndexType, PathIndexType, const PathIndexType);

  PathIndexType
  GetTrailingSetBits(const PathIndexType, const PathIndexType);

  PathIndexType
  GetDirection(const PathIndexType, const PathIndexType);

  PathIndexType
  GetEntry(const PathIndexType);

  PathIndexType
  GetBitRange(const PathIndexType, const PathIndexType, const PathIndexType, const PathIndexType);

  HilbertOrderType m_HilbertOrder{ 1 };
  HilbertPathType  m_HilbertPath{};
};
} // end namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#  include "itkHilbertPath.hxx"
#endif

#endif
