/* comet_elements.c     enters comet elements	*/
/* Based upon Earl Spillar's  comets.c          */
/* 95/11/24  R. Howell  -- Modified to correct prompts */
/*                         Also allows years > 1999    */

#include <math.h>
#include <stdio.h>

/* double cal_jd(int y,int m,double d); */
double cal_jd();


main()		/* Comets program */
{
	FILE *output_file;
	double transjul_date,q,omega,i;
	double epochjul_date,a,e,n,w,M=0.0,semdia=0.0,mag=0.0;
	char number[16], name[40],outfile[80],c='N';
	int		temp_day;		/* Temporarily holds day   of perihelion */
	double	temp_hr;		/* Temporarily holds hh.hh of perihelion */
	struct date{
		int year;
		int month;
		double day;
	}trans,epoch;


	printf("**** Enters Comet Orbit Elements ****\n");
	
		printf("Enter a number or ALTERNATE name for the comet: ");
		scanf("%15s",number);
		number[15] = 0;

		printf("Enter the name of the comet: ");
		scanf("%39s",name);
		name[39] = 0;			/* Make sure it is null terminated */
		
		printf("Enter the date of perihelion transit (yyyy mm dd hh.hh):");
		scanf("%d %d %d %lf", &trans.year, &trans.month, &temp_day, &temp_hr);
		trans.day = (double)temp_day + (temp_hr/24.);

		printf("Enter the distance at perihelion q: ");
		scanf("%lf",&q);
		
		printf("Enter the eccentricity e: ");
		scanf("%lf",&e);
		
		printf("Enter the argument of perihelion omega: ");
		scanf("%lf",&w);
		
		printf("Enter the longitude of ascending node Omega: ");
		scanf("%lf",&omega);
		
		printf("Enter the inclination i: ");
		scanf("%lf",&i);
		
		printf("Enter the daily motion n or 0.0 if unknown: ");
		scanf("%lf",&n);
		
		printf("Enter the equinox for the elements (yyyy mm dd): ");
		scanf("%d %d %lf",&epoch.year,&epoch.month,&epoch.day);

		transjul_date = (double) cal_jd(trans.year,
		trans.month,trans.day);

		epochjul_date = (double) cal_jd(epoch.year,
		epoch.month,epoch.day);
		a = q/(1-e);  /* convert perihelion to mean dist */

		printf("\nNumber:  %6s",number);
		printf("\nComet Name: %20s\n",name);
		printf("Date of Perihelion Transit (JD): %f\n",transjul_date);	
		printf("Mean Distance: %f\n",a); /* mean distance */
		printf("Eccentricity: %f\n",e);
		printf("Argument of Latitude: %f\n",w);
		printf("Longitude of Ascending Node: %f\n",omega);
		printf("Inclindation: %f\n",i);
		printf("Equinox (JD): %f\n",epochjul_date);
	

	printf("Enter name of output file: ");
	scanf("%s",outfile);
	output_file=fopen(outfile,"a");
	
	fprintf(output_file,"%6s %-20s %9.4f %10.5f %10.5f %10.5f %11.7f\n",
		number, name, transjul_date,i,omega,w,a);
	fprintf(output_file,"%10.5f %10.7f %10.7f %9.4f %7.3f %7.3f\n",
		n,e, M, epochjul_date,mag,semdia); 

}

double cal_jd(yyyy, m, d)   /* Conversion routine */
int yyyy;
int m;
double d;
{
	double B,jul_date;

	if (m <= 2){
		m = m + 12;
		yyyy = yyyy - 1;
	}
	
/*	yyyy = yyyy + 1900.0;	New version uses full year. */

	B = -15.0;	/* approximation only good between 1 March 1900 and */
				/* 28 February 2100                                  */
	
	jul_date = ((floor(365.25 * yyyy))+(floor(30.6001*(m+1)))+(B)+
	(1720996.5)+(d));
    
	return((double)jul_date);    
}