#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#ifndef _MAIN_H_
#define _MAIN_H_

#define DEFAULT_NSTEPS 150000
#define DEFAULT_TIMESTEP 10.0   /* femto-second */
#define DEFAULT_CUTOFF 5.0
#define DEFAULT_SWITCH_DIST 4.0
#define DEFAULT_SWTICH_METHOD SM_C2
#define LENGTH_UNIT 3.405  /* angstrom */
#define MASS_UNIT 39.95 /* AMU */
#define ENERGY_UNIT (120.0*8.314472135196751e-07/0.0004184)  /* KCAL/MOL */
#define TIME_UNIT (sqrt(MASS_UNIT*LENGTH_UNIT*LENGTH_UNIT/(120.0*8.314472135196751e-07)))  /* value = 2.1546e3 femto second */


enum {  /* swithing function continuity */
  SM_DC=0, SM_C0, SM_C1, SM_C2, SM_MAX_SWITCH_METHOD
}; 

const char *SWITH_METHOD_NAME[ SM_MAX_SWITCH_METHOD ];

typedef struct Data {

  /* SIMULATION PARAMETERS */
  double dt;         /* timestep */
  int natoms;        /* number of atoms in the system */
  int n, nsteps;     /* n is the current iteration, nsteps the total number */
  double pe, ke, energy; /* potential kinetic and total energy */

  /* PER ATOMS PARAMETERS */
  double *pos;       /* atom positions */
  double *vel;       /* atom velocities */
  double *f;         /* forces on each atom */
  double *mass;      /* atom masses */

  /* OUTPUT FILE PARAMETERS - 3 files are created by this program */
  FILE *sim_out;    /* energy, position, & velocity: <filename>.sim */
  
  int switch_method;
  double cutoff, switch_distance;
  double LJs, LJs_p, LJs_pp; /* potential & derivatives at switch distance */
  double systemsize;  /* periodic boundary conditon */

  const char *outfile;
} Data;

int initialize(Data *data);
int cleanup(Data *data);

void applyPBC(Data *data);

#endif /* _MAIN_H_ */