#include <stdio.h>


#define	BLKSIZ	512


char	ibuf[BLKSIZ];
int	blksiz = BLKSIZ;


int	dbgflg = 0;			/* Debug; print entry and value */


int	main(argc, argv)
	int	argc;
	char	*argv[];

{			char	*arg;
			char	*ofnm, *ifnm;
	register	FILE	*out, *in;
			int	ooffset, nblks;
			int	iwblks, inblks, ieblksz;
			int	olstblk, cblk, rdsz, wrsz;
			long	isize, osize;


	if ((argc < 5) || (argc > 6)) {
		printf("\ninsert {-d} <tfile> <sfile> <ooffset> <nblks>\n");
		exit(1);
		}

	argv++;
	argc--;
	

	for (;;) {
		arg = *argv;
		if (*arg++ != '-')
			break;

		argv++;
		argc--;

		switch (*arg) {

		  case 'd':	dbgflg++;
				printf("\n");
				break;

		  default:	printf("Bad flag: %c", *arg);
				exit(1);
		  }
		}


	ofnm = *argv++;
	argc--;
	
	out = fopen(ofnm, "r+b");
	if (out == NULL) {
		printf("Error opening output file: '%s'\n", ofnm);
		exit(1);
		}

	ifnm = *argv++;
	argc--;
	
	in = fopen(ifnm, "rb");
	if (in == NULL) {
		printf("Error opening input file: '%s'\n", ifnm);
		exit(1);
		}



	ooffset = atoi(*argv++);
	if (ooffset < 0) {
		printf("Bad offset: %d\n", ooffset);
		exit(1);
		}

	argc--;

	nblks = atoi(*argv++);
	if (nblks < 0) {
		printf("Bad size: %d\n", nblks);
		exit(1);
		}

	if (--argc > 0) {
		printf("Unneeded extra arg '%s'", *argv);
		exit(1);		
		}


	if (fseek(in, 0, SEEK_END) != 0) {
		printf("Xfer size seek failed\n");
		exit(1);
		}

	isize = ftell(in);
	iwblks = (isize / BLKSIZ);
	ieblksz = (isize % BLKSIZ);
	inblks = iwblks;
	
	if (ieblksz == 0)
		ieblksz = BLKSIZ;
	  else
		inblks++;


	if (nblks == 0)
		nblks = inblks;

	if (nblks > inblks) {
		printf("Block number/size too large\n");
		exit(1);
		}
	
	olstblk = (ooffset + nblks - 1);

	printf("\nStart/End Block: %d %d\n", ooffset, olstblk);
	printf("Size: %ld %d %d\n", isize, iwblks, ieblksz);


/*	// Strictly speaking, seek not needed with "a"

	if (fseek(out, 0, SEEK_END) != 0) {
		printf("Space size seek failed\n");
		exit(1);
		}

	osize = ftell(out);	*/


	if (fseek(in, 0, SEEK_SET) != 0) {
		printf("Read seek failed\n");
		exit(1);
		}

	if (fseek(out, (ooffset * BLKSIZ), SEEK_SET) != 0) {
		printf("Write seek failed\n");
		exit(1);
		}
	

	for (cblk = ooffset; (cblk <= olstblk); cblk++) {
		if (cblk == olstblk)
			blksiz = ieblksz;

		if ((rdsz = fread(&ibuf[0], sizeof(char), blksiz, in)) != blksiz) {
			printf("Read failed: block %d read %d\n", cblk, rdsz);
			exit(1);
			}

		if ((wrsz = fwrite(&ibuf[0], sizeof(char), blksiz, out)) != blksiz) {
			printf("Write failed: block %d write %d\n", cblk, wrsz);
			exit(1);
			}
		}


	fclose(in);
	fclose(out);

	printf("%d blocks read\n", (cblk - ooffset));
}