#ifndef OPENMM_PERIODICTORSIONFORCE_H_
#define OPENMM_PERIODICTORSIONFORCE_H_

/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit.                   *
 * See https://openmm.org/development.                                        *
 *                                                                            *
 * Portions copyright (c) 2008-2024 Stanford University and the Authors.      *
 * Authors: Peter Eastman                                                     *
 * Contributors:                                                              *
 *                                                                            *
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 * copy of this software and associated documentation files (the "Software"), *
 * to deal in the Software without restriction, including without limitation  *
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 * and/or sell copies of the Software, and to permit persons to whom the      *
 * Software is furnished to do so, subject to the following conditions:       *
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 * The above copyright notice and this permission notice shall be included in *
 * all copies or substantial portions of the Software.                        *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
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 * -------------------------------------------------------------------------- */

#include "Force.h"
#include "Vec3.h"
#include <map>
#include <vector>
#include "internal/windowsExport.h"

namespace OpenMM {

/**
 * This class implements an interaction between groups of four particles that varies periodically with the torsion angle
 * between them.  To use it, create a PeriodicTorsionForce object then call addTorsion() once for each torsion.  After
 * a torsion has been added, you can modify its force field parameters by calling setTorsionParameters().  This will
 * have no effect on Contexts that already exist unless you call updateParametersInContext().
 */

class OPENMM_EXPORT PeriodicTorsionForce : public Force {
public:
    /**
     * Create a PeriodicTorsionForce.
     */
    PeriodicTorsionForce();
    /**
     * Get the number of periodic torsion terms in the potential function
     */
    int getNumTorsions() const;
    /**
     * Add a periodic torsion term to the force field.
     *
     * @param particle1    the index of the first particle forming the torsion
     * @param particle2    the index of the second particle forming the torsion
     * @param particle3    the index of the third particle forming the torsion
     * @param particle4    the index of the fourth particle forming the torsion
     * @param periodicity  the periodicity of the torsion
     * @param phase        the phase offset of the torsion, measured in radians
     * @param k            the force constant for the torsion
     * @return the index of the torsion that was added
     */
    int addTorsion(int particle1, int particle2, int particle3, int particle4, int periodicity, double phase, double k);
    /**
     * Get the force field parameters for a periodic torsion term.
     *
     * @param index             the index of the torsion for which to get parameters
     * @param[out] particle1    the index of the first particle forming the torsion
     * @param[out] particle2    the index of the second particle forming the torsion
     * @param[out] particle3    the index of the third particle forming the torsion
     * @param[out] particle4    the index of the fourth particle forming the torsion
     * @param[out] periodicity  the periodicity of the torsion
     * @param[out] phase        the phase offset of the torsion, measured in radians
     * @param[out] k            the force constant for the torsion
     */
    void getTorsionParameters(int index, int& particle1, int& particle2, int& particle3, int& particle4, int& periodicity, double& phase, double& k) const;
    /**
     * Set the force field parameters for a periodic torsion term.
     *
     * @param index        the index of the torsion for which to set parameters
     * @param particle1    the index of the first particle forming the torsion
     * @param particle2    the index of the second particle forming the torsion
     * @param particle3    the index of the third particle forming the torsion
     * @param particle4    the index of the fourth particle forming the torsion
     * @param periodicity  the periodicity of the torsion
     * @param phase        the phase offset of the torsion, measured in radians
     * @param k            the force constant for the torsion
     */
    void setTorsionParameters(int index, int particle1, int particle2, int particle3, int particle4, int periodicity, double phase, double k);
    /**
     * Update the per-torsion parameters in a Context to match those stored in this Force object.  This method provides
     * an efficient method to update certain parameters in an existing Context without needing to reinitialize it.
     * Simply call setTorsionParameters() to modify this object's parameters, then call updateParametersInContext()
     * to copy them over to the Context.
     *
     * The only information this method updates is the values of per-torsion parameters.  The set of particles involved
     * in a torsion cannot be changed, nor can new torsions be added.
     */
    void updateParametersInContext(Context& context);
    /**
     * Set whether this force should apply periodic boundary conditions when calculating displacements.
     * Usually this is not appropriate for bonded forces, but there are situations when it can be useful.
     */
    void setUsesPeriodicBoundaryConditions(bool periodic);
    /**
     * Returns whether or not this force makes use of periodic boundary
     * conditions.
     *
     * @returns true if force uses PBC and false otherwise
     */
    bool usesPeriodicBoundaryConditions() const;
protected:
    ForceImpl* createImpl() const;
private:
    class PeriodicTorsionInfo;
    std::vector<PeriodicTorsionInfo> periodicTorsions;
    bool usePeriodic;
    mutable int numContexts, firstChangedTorsion, lastChangedTorsion;
};

/**
 * This is an internal class used to record information about a torsion.
 * @private
 */
class PeriodicTorsionForce::PeriodicTorsionInfo {
public:
    int particle1, particle2, particle3, particle4, periodicity;
    double phase, k;
    PeriodicTorsionInfo() {
        particle1 = particle2 = particle3 = particle4 = -1;
        periodicity = 1;
        phase = k = 0.0;
    }
    PeriodicTorsionInfo(int particle1, int particle2, int particle3, int particle4, int periodicity, double phase, double k) :
        particle1(particle1), particle2(particle2), particle3(particle3), particle4(particle4), periodicity(periodicity), phase(phase), k(k) {
    }
};

} // namespace OpenMM

#endif /*OPENMM_PERIODICTORSIONFORCE_H_*/
