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

int main(int argc, char* argv[])
/* program to split 4-column file when slope of first column changes sign */
/* writes files <yourfile>.0, <yourfile>.1, etc. */
{
	FILE* inFile;
	FILE* outFile;
	int nFile, nRead, goodLines, i;
	double c1, c2, c3, c4, c5;
	double p1, p2, p3, p4;
	double pp1, pp2, pp3, pp4;
	double dum, pp, cp;
	char outName[100];
	char line[100];
	
	/* check command line argument count */
	if (argc != 2)
	{
		printf("Split [filename]\n");
		exit(1);
	}
	
	/* open input file */
	inFile=fopen(argv[1],"r");
	
	/* check for open error */
	if (inFile == NULL)
	{
		printf("Error opening input file='%s'\n", argv[1]);
		exit(1);
	}
	
	printf("Opened input file '%s'\n", argv[1]);
	
	/* name of first output file */
	nFile=0;
	sprintf(outName,"%s.%i", argv[1], nFile);
	
	/* open first output file */
	outFile=fopen(outName,"w");

	/* check for open error */
	if (outFile == NULL)
	{
		printf("Error opening output file='%s'\n", outName);
		exit(1);
	}
	
	/* init good lines */
	goodLines = 0;

	/* loop over lines */
	for (i=1; i<10000; i++)
	{
		/* read line of input file into string array */
		fgets(line, 99, inFile);
		
		/* check for end of file */
		if (feof(inFile))
		{
			printf("end of input file at line=%i\n", i);
			break;
		}
		
		/* skip line if first character is # */
		if (line[0] == '#')
		{
			printf("%3i: %s", i, line);
			printf("line=%i skipped\n", i);
			continue;
		}
		/* read string to count variables */
		nRead=sscanf(line,"%lf %lf %lf %lf %lf", &dum, &dum, &dum, &dum, &dum);

		/* check how many were read */
		if (nRead <= 0)
		{
			printf("%3i: %s", i, line);
			printf("line=%i skipped\n", i);
			continue;
		}
		if (nRead != 4)
		{
			printf("%3i: %s", i, line);
			printf("Error parsing line=%i, expected 4 numbers, found %i\n", i, nRead);
			printf("error exit\n");
			exit(1);
		}
		/* increment good line counter */
		goodLines++;

		/* shift previous values */
		pp1 = p1;
		pp2 = p2;
		pp3 = p3;
		pp4 = p4;
		p1 = c1;
		p2 = c2;
		p3 = c3;
		p4 = c4;

		/* read string into character variables */
		nRead=sscanf(line,"%lf %lf %lf %lf %lf", &c1, &c2, &c3, &c4, &c5);

		/* check that buffers are up to date */
		if (goodLines > 2)
		{
			/* write the data from 2 lines ago */
			fprintf(outFile,"%f \t %f \t %f \t %f\n", pp1, pp2, pp3, pp4);

			/* calculate differences */
			cp = c1 - p1;
			pp = p1 - pp1;

			/* check if slope changed sign */
			if ((pp > 0 && cp <= 0) || (pp < 0 && cp >= 0) )
			{
				/* close present file */
				fclose(outFile);
				printf("line=%i, closed output file '%s'\n", i, outName);
			
				/* name of next output file */
				nFile++;
				sprintf(outName,"%s.%i", argv[1], nFile);
			
				/* open next output file */
				outFile=fopen(outName,"w");

				/* check for open error */
				if (outFile == NULL)
				{
					printf("Error opening output file'%s'\n", outName);
					exit(1);
				}

				/* arrange to skip ambiguous data */
				goodLines = 1;
			}
		}
	}

	/* close present file */
	fclose(outFile);
	printf("line=%i, closed output file '%s'\n", i, outName);
	
	return 0;
}