/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
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 * This is part of the OpenMM molecular simulation toolkit.                   *
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 * Authors: Peter Eastman                                                     *
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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::setTemperature(double temp) {
    if (temp < 0)
        throw OpenMMException("Temperature cannot be negative");
    temperature = temp;
}

void VariableLangevinIntegrator::setFriction(double coeff) {
    if (coeff < 0)
        throw OpenMMException("Friction cannot be negative");
    friction = coeff;
}

void VariableLangevinIntegrator::setErrorTolerance(double tol) {
    if (tol <= 0)
        throw OpenMMException("Error tolerance must be positive");
    errorTol = tol;
}

void VariableLangevinIntegrator::setMaximumStepSize(double size) {
    if (size < 0)
        throw OpenMMException("Maximum step size cannot be negative");
    maxStepSize = size;
}

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

vector<string> VariableLangevinIntegrator::getKernelNames() {
    return {IntegrateVariableLangevinStepKernel::Name()};
}

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));
    }
}
