/*  dynamo:- Event driven molecular dynamics simulator
    http://www.marcusbannerman.co.uk/dynamo
    Copyright (C) 2011  Marcus N Campbell Bannerman <m.bannerman@gmail.com>

    This program is free software: you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    version 3 as published by the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#pragma once

#include <boost/numeric/ublas/vector.hpp>
#include <boost/numeric/ublas/vector_proxy.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/triangular.hpp>
#include <boost/numeric/ublas/lu.hpp>
#include <exception>

namespace ublas = boost::numeric::ublas;

class Spline : private std::vector<std::pair<double, double> >
{
public:
  //The boundary conditions available
  enum BC_type {
	FIXED_1ST_DERIV_BC,
	FIXED_2ND_DERIV_BC,
	PARABOLIC_RUNOUT_BC
  };

  enum Spline_type {
	LINEAR,
	CUBIC
  };

  //Constructor takes the boundary conditions as arguments, this
  //sets the first derivative (gradient) at the lower and upper
  //end points
  Spline():
	_valid(false),
	_BCLow(FIXED_2ND_DERIV_BC), _BCHigh(FIXED_2ND_DERIV_BC),
	_BCLowVal(0), _BCHighVal(0),
	_type(CUBIC)
  {}

  typedef std::vector<std::pair<double, double> > base;
  typedef base::const_iterator const_iterator;

  //Standard STL read-only container stuff
  const_iterator begin() const { return base::begin(); }
  const_iterator end() const { return base::end(); }
  void clear() { _valid = false; base::clear(); _data.clear(); }
  size_t size() const { return base::size(); }
  size_t max_size() const { return base::max_size(); }
  size_t capacity() const { return base::capacity(); }
  bool empty() const { return base::empty(); }

  //Add a point to the spline, and invalidate it so its
  //recalculated on the next access
  inline void addPoint(double x, double y)
  {
	_valid = false;
	base::push_back(std::pair<double, double>(x,y));
  }

  //Reset the boundary conditions
  inline void setLowBC(BC_type BC, double val = 0)
  { _BCLow = BC; _BCLowVal = val; _valid = false; }

  inline void setHighBC(BC_type BC, double val = 0)
  { _BCHigh = BC; _BCHighVal = val; _valid = false; }

  void setType(Spline_type type) { _type = type; _valid = false; }

  //Check if the spline has been calculated, then generate the
  //spline interpolated value
  double operator()(double xval)
  {
	if (!_valid) generate();

	//Special cases when we're outside the range of the spline points
	if (xval <= x(0)) return lowCalc(xval);
	if (xval >= x(size()-1)) return highCalc(xval);

	//Check all intervals except the last one
	for (std::vector<SplineData>::const_iterator iPtr = _data.begin();
		 iPtr != _data.end()-1; ++iPtr)
		if ((xval >= iPtr->x) && (xval <= (iPtr+1)->x))
		  return splineCalc(iPtr, xval);

	return splineCalc(_data.end() - 1, xval);
  }

private:

  ///////PRIVATE DATA MEMBERS
  struct SplineData { double x,a,b,c,d; };
  //vector of calculated spline data
  std::vector<SplineData> _data;
  //Second derivative at each point
  ublas::vector<double> _ddy;
  //Tracks whether the spline parameters have been calculated for
  //the current set of points
  bool _valid;
  //The boundary conditions
  BC_type _BCLow, _BCHigh;
  //The values of the boundary conditions
  double _BCLowVal, _BCHighVal;

  Spline_type _type;

  ///////PRIVATE FUNCTIONS
  //Function to calculate the value of a given spline at a point xval
  inline double splineCalc(std::vector<SplineData>::const_iterator i, double xval)
  {
	const double lx = xval - i->x;
	return ((i->a * lx + i->b) * lx + i->c) * lx + i->d;
  }

  inline double lowCalc(double xval)
  {
	const double lx = xval - x(0);

	if (_type == LINEAR)
	  return lx * _BCHighVal + y(0);

	const double firstDeriv = (y(1) - y(0)) / h(0) - 2 * h(0) * (_data[0].b + 2 * _data[1].b) / 6;

	switch(_BCLow)
	  {
	  case FIXED_1ST_DERIV_BC:
		return lx * _BCLowVal + y(0);
	  case FIXED_2ND_DERIV_BC:
		  return lx * lx * _BCLowVal + firstDeriv * lx + y(0);
	  case PARABOLIC_RUNOUT_BC:
		return lx * lx * _ddy[0] + lx * firstDeriv  + y(0);
	  }
	throw std::runtime_error("Unknown BC");
  }

  inline double highCalc(double xval)
  {
	const double lx = xval - x(size() - 1);

	if (_type == LINEAR)
	  return lx * _BCHighVal + y(size() - 1);

	const double firstDeriv = 2 * h(size() - 2) * (_ddy[size() - 2] + 2 * _ddy[size() - 1]) / 6 + (y(size() - 1) - y(size() - 2)) / h(size() - 2);

	switch(_BCHigh)
	  {
	  case FIXED_1ST_DERIV_BC:
		return lx * _BCHighVal + y(size() - 1);
	  case FIXED_2ND_DERIV_BC:
		return lx * lx * _BCHighVal + firstDeriv * lx + y(size() - 1);
	  case PARABOLIC_RUNOUT_BC:
		return lx * lx * _ddy[size()-1] + lx * firstDeriv  + y(size() - 1);
	  }
	throw std::runtime_error("Unknown BC");
  }

  //These just provide access to the point data in a clean way
  inline double x(size_t i) const { return operator[](i).first; }
  inline double y(size_t i) const { return operator[](i).second; }
  inline double h(size_t i) const { return x(i+1) - x(i); }

  //Invert a arbitrary matrix using the boost ublas library
  template<class T>
  bool InvertMatrix(ublas::matrix<T> A,
		ublas::matrix<T>& inverse)
  {
	using namespace ublas;

	// create a permutation matrix for the LU-factorization
	permutation_matrix<std::size_t> pm(A.size1());

	// perform LU-factorization
	int res = lu_factorize(A,pm);
		if( res != 0 ) return false;

	// create identity matrix of "inverse"
	inverse.assign(ublas::identity_matrix<T>(A.size1()));

	// backsubstitute to get the inverse
	lu_substitute(A, pm, inverse);

	return true;
  }

  //This function will recalculate the spline parameters and store
  //them in _data, ready for spline interpolation
  void generate()
  {
	if (size() < 2)
	  throw std::runtime_error("Spline requires at least 2 points");

	//If any spline points are at the same x location, we have to
	//just slightly seperate them
	{
	  bool testPassed(false);
	  while (!testPassed)
		{
		  testPassed = true;
		  std::sort(base::begin(), base::end());

		  for (base::iterator iPtr = base::begin(); iPtr != base::end() - 1; ++iPtr)
		if (iPtr->first == (iPtr+1)->first)
		  {
			if ((iPtr+1)->first != 0)
			  (iPtr+1)->first += (iPtr+1)->first
			* std::numeric_limits<double>::epsilon() * 10;
			else
			  (iPtr+1)->first = std::numeric_limits<double>::epsilon() * 10;
			testPassed = false;
			break;
		  }
		}
	}

	const size_t e = size() - 1;

	switch (_type)
	  {
	  case LINEAR:
		{
		  _data.resize(e);
		  for (size_t i(0); i < e; ++i)
		{
		  _data[i].x = x(i);
		  _data[i].a = 0;
		  _data[i].b = 0;
		  _data[i].c = (y(i+1) - y(i)) / (x(i+1) - x(i));
		  _data[i].d = y(i);
		}
		  break;
		}
	  case CUBIC:
		{
		  ublas::matrix<double> A(size(), size());
		  for (size_t yv(0); yv <= e; ++yv)
		for (size_t xv(0); xv <= e; ++xv)
		  A(xv,yv) = 0;

		  for (size_t i(1); i < e; ++i)
		{
		  A(i-1,i) = h(i-1);
		  A(i,i) = 2 * (h(i-1) + h(i));
		  A(i+1,i) = h(i);
		}

		  ublas::vector<double> C(size());
		  for (size_t xv(0); xv <= e; ++xv)
		C(xv) = 0;

		  for (size_t i(1); i < e; ++i)
		C(i) = 6 *
		  ((y(i+1) - y(i)) / h(i)
		   - (y(i) - y(i-1)) / h(i-1));

		  //Boundary conditions
		  switch(_BCLow)
		{
		case FIXED_1ST_DERIV_BC:
		  C(0) = 6 * ((y(1) - y(0)) / h(0) - _BCLowVal);
		  A(0,0) = 2 * h(0);
		  A(1,0) = h(0);
		  break;
		case FIXED_2ND_DERIV_BC:
		  C(0) = _BCLowVal;
		  A(0,0) = 1;
		  break;
		case PARABOLIC_RUNOUT_BC:
		  C(0) = 0; A(0,0) = 1; A(1,0) = -1;
		  break;
		}

		  switch(_BCHigh)
		{
		case FIXED_1ST_DERIV_BC:
		  C(e) = 6 * (_BCHighVal - (y(e) - y(e-1)) / h(e-1));
		  A(e,e) = 2 * h(e - 1);
		  A(e-1,e) = h(e - 1);
		  break;
		case FIXED_2ND_DERIV_BC:
		  C(e) = _BCHighVal;
		  A(e,e) = 1;
		  break;
		case PARABOLIC_RUNOUT_BC:
		  C(e) = 0; A(e,e) = 1; A(e-1,e) = -1;
		  break;
		}

		  ublas::matrix<double> AInv(size(), size());
		  InvertMatrix(A,AInv);

		  _ddy = ublas::prod(C, AInv);

		  _data.resize(size()-1);
		  for (size_t i(0); i < e; ++i)
		{
		  _data[i].x = x(i);
		  _data[i].a = (_ddy(i+1) - _ddy(i)) / (6 * h(i));
		  _data[i].b = _ddy(i) / 2;
		  _data[i].c = (y(i+1) - y(i)) / h(i) - _ddy(i+1) * h(i) / 6 - _ddy(i) * h(i) / 3;
		  _data[i].d = y(i);
		}
		}
	  }
	_valid = true;
  }
};