/*********************************************************************/
/* pnmshift -  shift lines of a picture left or right by x xels      */
/* Frank Neumann, October 1993                                       */
/* V1.2 27.11.1999                                                   */
/*                                                                   */
/* version history:                                                  */
/* V1.0    11.10.1993  first version                                 */
/* V1.1    16.11.1993  Rewritten to be NetPBM.programming conforming */
/* V1.2    27.11.1999  Promoted from ppmshift to pnmshift.           */
/*********************************************************************/

#include <time.h>
#include "pnm.h"

/* global variables */
#ifdef AMIGA
static char *version = "$VER: pnmshift 1.2 (27.11.99)"; /* Amiga version identification */
#endif

/**************************/
/* start of main function */
/**************************/
int
main( int argc, char* argv[] )
{
	FILE* ifp;
	int argn, rows, cols, format, i = 0, j = 0;
	xel *srcrow, *destrow;
	xel *xP = NULL, *xP2 = NULL;
	xelval maxval;
	int shift, nowshift;
	char *usage = "shift [pnmfile]\n        shift: maximum number of xels to shift a line by\n";

	/* parse in 'default' parameters */
	pnm_init(&argc, argv);

	argn = 1;

	/* parse in shift number */
	if (argn == argc)
		pm_usage(usage);
	if (sscanf(argv[argn], "%d", &shift) != 1)
		pm_usage(usage);
	if (shift < 0)
		pm_error("shift factor must be 0 or more");
	++argn;

	/* parse in filename (if present, stdin otherwise) */
	if (argn != argc)
	{
		ifp = pm_openr(argv[argn]);
		++argn;
	}
	else
		ifp = stdin;

	if (argn != argc)
		pm_usage(usage);

	/* read first data from file */
	pnm_readpnminit(ifp, &cols, &rows, &maxval, &format);

	if (shift > cols)
	{
		shift = cols;
		pm_message("shift amount is larger than picture width - reset to %d", shift);
	}

	/* no error checking required here, pnmlib does it all for us */
	srcrow = pnm_allocrow(cols);

	/* allocate a row of xel data for the new xels */
	destrow = pnm_allocrow(cols);

	pnm_writepnminit(stdout, cols, rows, maxval, format, 0);

	/* get time of day to feed the random number generator */
	srandom( time( (time_t*) 0 ) );

	/** now do the shifting **/
	/* the range by which a line is shifted lays in the range from */
	/* -shift/2 .. +shift/2 xels; however, within this range it is */
	/* randomly chosen */
	for (i = 0; i < rows; i++)
	{
		if (shift != 0)
			nowshift = (random() % (shift+1)) - ((shift+1) / 2);
		else
			nowshift = 0;

		pnm_readpnmrow(ifp, srcrow, cols, maxval, format);

		xP = srcrow;
		xP2 = destrow;

		/* if the shift value is less than zero, we take the original xel line and */
		/* copy it into the destination line translated to the left by x xels. The */
		/* empty xels on the right end of the destination line are filled up with  */
		/* the xel that is the right-most in the original xel line.              */
		if (nowshift < 0)
		{
			xP+= abs(nowshift);
			for (j = 0; j < cols; j++)
			{
				*xP2 = *xP;
				xP2++;
				if (j < (cols+nowshift)-1)
					xP++;
			}
		}
		/* if the shift value is 0 or positive, the first <nowshift> xels of the */
		/* destination line are filled with the first xel from the source line,  */
		/* and the rest of the source line is copied to the dest line            */
		else
		{
			for (j = 0; j < cols; j++)
			{
				*xP2 = *xP;
				xP2++;
				if (j >= nowshift)
					xP++;
			}
		}

		/* write out one line of graphic data */
		pnm_writepnmrow(stdout, destrow, cols, maxval, format, 0);
	}

	pm_closer(ifp);
	pm_closew(stdout);
	pnm_freerow(srcrow);
	pnm_freerow(destrow);

	exit(0);
}