/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit originating from   *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org.               *
 *                                                                            *
 * Portions copyright (c) 2008-2020 Stanford University and the Authors.      *
 * Authors: Peter Eastman                                                     *
 * Contributors:                                                              *
 *                                                                            *
 * Permission is hereby granted, free of charge, to any person obtaining a    *
 * copy of this software and associated documentation files (the "Software"), *
 * to deal in the Software without restriction, including without limitation  *
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
 * 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 "openmm/VariableLangevinIntegrator.h"
#include "openmm/Context.h"
#include "openmm/OpenMMException.h"
#include "openmm/internal/ContextImpl.h"
#include "openmm/kernels.h"
#include <limits>
#include <string>


using namespace OpenMM;
using std::string;
using std::vector;

VariableLangevinIntegrator::VariableLangevinIntegrator(double temperature, double frictionCoeff, double errorTol) {
    setTemperature(temperature);
    setFriction(frictionCoeff);
    setErrorTolerance(errorTol);
    setMaximumStepSize(0.0);
    setConstraintTolerance(1e-5);
    setRandomNumberSeed(0);
    setStepSize(0.0);
}

void VariableLangevinIntegrator::initialize(ContextImpl& contextRef) {
    if (owner != NULL && &contextRef.getOwner() != owner)
        throw OpenMMException("This Integrator is already bound to a context");
    context = &contextRef;
    owner = &contextRef.getOwner();
    kernel = context->getPlatform().createKernel(IntegrateVariableLangevinStepKernel::Name(), contextRef);
    kernel.getAs<IntegrateVariableLangevinStepKernel>().initialize(contextRef.getSystem(), *this);
}

void VariableLangevinIntegrator::cleanup() {
    kernel = Kernel();
}

vector<string> VariableLangevinIntegrator::getKernelNames() {
    std::vector<std::string> names;
    names.push_back(IntegrateVariableLangevinStepKernel::Name());
    return names;
}

double VariableLangevinIntegrator::computeKineticEnergy() {
    return kernel.getAs<IntegrateVariableLangevinStepKernel>().computeKineticEnergy(*context, *this);
}

void VariableLangevinIntegrator::step(int steps) {
    if (context == NULL)
        throw OpenMMException("This Integrator is not bound to a context!");  
    for (int i = 0; i < steps; ++i) {
        context->updateContextState();
        context->calcForcesAndEnergy(true, false, getIntegrationForceGroups());
        setStepSize(kernel.getAs<IntegrateVariableLangevinStepKernel>().execute(*context, *this, std::numeric_limits<double>::infinity()));
    }
}

void VariableLangevinIntegrator::stepTo(double time) {
    if (context == NULL)
        throw OpenMMException("This Integrator is not bound to a context!");
    while (time > context->getTime()) {
        context->updateContextState();
        context->calcForcesAndEnergy(true, false, getIntegrationForceGroups());
        setStepSize(kernel.getAs<IntegrateVariableLangevinStepKernel>().execute(*context, *this, time));
    }
}
