HarmonicAngleForce

// ******************************************************************************
//
// Title:       Force Field X.
// Description: Force Field X - Software for Molecular Biophysics.
// Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
//
// This file is part of Force Field X.
//
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package ffx.openmm;

import com.sun.jna.ptr.DoubleByReference;
import com.sun.jna.ptr.IntByReference;

import java.nio.DoubleBuffer;
import java.nio.IntBuffer;

import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_Boolean.OpenMM_True;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_addAngle;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_create;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_destroy;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_getAngleParameters;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_getNumAngles;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_setAngleParameters;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_setUsesPeriodicBoundaryConditions;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_updateParametersInContext;
import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_HarmonicAngleForce_usesPeriodicBoundaryConditions;

/**
 * This class implements an interaction between groups of three particles that varies harmonically with the angle
 * between them.  To use it, create a HarmonicAngleForce object then call addAngle() once for each angle.  After
 * an angle has been added, you can modify its force field parameters by calling setAngleParameters().  This will
 * have no effect on Contexts that already exist unless you call updateParametersInContext().
 */
public class HarmonicAngleForce extends Force {

  /**
   * Create a new HarmonicAngleForce.
   */
  public HarmonicAngleForce() {
    super(OpenMM_HarmonicAngleForce_create());
  }

  /**
   * Add an angle term to the force field.
   *
   * @param particle1 The index of the first particle forming the angle.
   * @param particle2 The index of the second particle forming the angle.
   * @param particle3 The index of the third particle forming the angle.
   * @param angle     The equilibrium angle, measured in radians.
   * @param k         The harmonic force constant for the angle, measured in kJ/mol/radian&circ;2.
   * @return The index of the angle that was added.
   */
  public int addAngle(int particle1, int particle2, int particle3, double angle, double k) {
    return OpenMM_HarmonicAngleForce_addAngle(pointer, particle1, particle2, particle3, angle, k);
  }

  /**
   * Destroy the force.
   */
  @Override
  public void destroy() {
    if (pointer != null) {
      OpenMM_HarmonicAngleForce_destroy(pointer);
      pointer = null;
    }
  }

  /**
   * Get the force field parameters for an angle term.
   *
   * @param index     The index of the angle for which to get parameters.
   * @param particle1 The index of the first particle forming the angle (output).
   * @param particle2 The index of the second particle forming the angle (output).
   * @param particle3 The index of the third particle forming the angle (output).
   * @param angle     The equilibrium angle, measured in radians (output).
   * @param k         The harmonic force constant for the angle, measured in kJ/mol/radian&circ;2 (output).
   */
  public void getAngleParameters(int index, IntByReference particle1, IntByReference particle2,
                                 IntByReference particle3, DoubleByReference angle, DoubleByReference k) {
    OpenMM_HarmonicAngleForce_getAngleParameters(pointer, index, particle1, particle2, particle3, angle, k);
  }

  /**
   * Get the force field parameters for an angle term.
   *
   * @param index     The index of the angle for which to get parameters.
   * @param particle1 The index of the first particle forming the angle (output).
   * @param particle2 The index of the second particle forming the angle (output).
   * @param particle3 The index of the third particle forming the angle (output).
   * @param angle     The equilibrium angle, measured in radians (output).
   * @param k         The harmonic force constant for the angle, measured in kJ/mol/radian&circ;2 (output).
   */
  public void getAngleParameters(int index, IntBuffer particle1, IntBuffer particle2,
                                 IntBuffer particle3, DoubleBuffer angle, DoubleBuffer k) {
    OpenMM_HarmonicAngleForce_getAngleParameters(pointer, index, particle1, particle2, particle3, angle, k);
  }

  /**
   * Get the number of angles in the force.
   *
   * @return The number of angles.
   */
  public int getNumAngles() {
    return OpenMM_HarmonicAngleForce_getNumAngles(pointer);
  }

  /**
   * Set the force field parameters for an angle term.
   *
   * @param index     The index of the angle for which to set parameters.
   * @param particle1 The index of the first particle forming the angle.
   * @param particle2 The index of the second particle forming the angle.
   * @param particle3 The index of the third particle forming the angle.
   * @param angle     The equilibrium angle, measured in radians.
   * @param k         The harmonic force constant for the angle, measured in kJ/mol/radian&circ;2.
   */
  public void setAngleParameters(int index, int particle1, int particle2, int particle3, double angle, double k) {
    OpenMM_HarmonicAngleForce_setAngleParameters(pointer, index, particle1, particle2, particle3, angle, k);
  }

  /**
   * Set whether this force should apply periodic boundary conditions when calculating displacements.
   *
   * @param periodic If true, periodic boundary conditions will be applied.
   */
  public void setUsesPeriodicBoundaryConditions(boolean periodic) {
    OpenMM_HarmonicAngleForce_setUsesPeriodicBoundaryConditions(pointer, periodic ? 1 : 0);
  }

  /**
   * Update the parameters in the OpenMM Context.
   *
   * @param context The OpenMM Context.
   */
  public void updateParametersInContext(Context context) {
    if (context.hasContextPointer()) {
      OpenMM_HarmonicAngleForce_updateParametersInContext(pointer, context.getPointer());
    }
  }

  /**
   * Check if the force uses periodic boundary conditions.
   *
   * @return True if the force uses periodic boundary conditions.
   */
  @Override
  public boolean usesPeriodicBoundaryConditions() {
    int pbc = OpenMM_HarmonicAngleForce_usesPeriodicBoundaryConditions(pointer);
    return pbc == OpenMM_True;
  }
}