/*
 * copy input file to backup file.  If in_name is /blah/blah/blah/file, then
 * backup file will be "file.BAK".  Then make the backup file the input and
 * original input file the output.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#ifdef __TURBOC__
#include <io.h>
#include <alloc.h>
#else
#include <errno.h>
extern *sys_errlist[];
#endif


extern char *ProgName;


#define WARN(msg,param) {\
		(void) fprintf(stderr, \
			"%s: Error %s \"%s\" - %s\n",\
			ProgName,msg,param,sys_errlist[errno]\
		);\
		++nerrs;\
}

#define FATAL(msg,param) {\
		WARN(msg,param);\
		if (BackFileName != (char *)0) {\
			if (unlink(BackFileName) != 0) \
				WARN("removing",BackFileName);\
			(void) free(BackFileName);\
		}\
		return nerrs;\
}


int ProcessFile(InputFileName,ProcessFunc)
char *InputFileName;
int (*ProcessFunc)();
{
	char *BackFileName = (char *)0;
	int nerrs = 0;
	FILE *fin;
	FILE *fout;

	if ((fin = fopen(InputFileName,"r")) == (FILE *)0)
		FATAL("opening",InputFileName);
	{
		static char BAK[] = ".BAK";
		int len = strlen(InputFileName) + sizeof(BAK);

		if ((BackFileName = malloc(len)) == (char *)0) {
			(void) fprintf(stderr,
					"%s: Cannot malloc %d bytes for %s%s\n",
					ProgName,len,InputFileName,BAK
			);
			return ++nerrs;
		}
		(void) sprintf(BackFileName,"%s%s",InputFileName,BAK);
		assert(1 + strlen(BackFileName) == len);
	}
	/* 
	**	copy InputFileName to backup file
	*/
	{
		int  bakchn;

		if ((bakchn = creat(BackFileName, 0600)) < 0)
			FATAL("create",BackFileName);
		
		{
			int n;
			char buff[BUFSIZ];

			while ((n = read(fileno(fin), buff, sizeof buff)) > 0) 
				if (write(bakchn, buff, n) != n) 
					FATAL("writing to",BackFileName);
			if (n < 0) 
				FATAL("reading from",InputFileName);
			if (close(bakchn) != 0) 
				WARN("closing",BackFileName);
			if (fclose(fin) != 0) 
				WARN("closing",InputFileName);
		}
	}
	/* 
	**	re-open backup file as the input file
	*/
	if ((fin = fopen(BackFileName, "r")) == (FILE *)0)
		FATAL("re-opening",BackFileName);
	/*
	**	now the original input file will be the output
	*/
	if ((fout = fopen(InputFileName, "w")) == (FILE *)0)
		FATAL("re-opening",InputFileName);
	if (ProcessFunc(fin,fout) != 0) {
		(void) fprintf(stderr,
			"%s: Could not process file \"%s\"\n",
			ProgName,InputFileName
		);
		if (rename(BackFileName,InputFileName) == 0) {
			(void) fprintf(stderr,
"%s: Cannot recover original contents of \"%s\"\n\
   Original contents should be in \"%s\"\n",
				ProgName,InputFileName,BackFileName
			);
			nerrs++;
		}
	} else {
		if (fclose(fin) != 0) 
			WARN("closing",BackFileName);
		if (fclose(fout) != 0) 
			WARN("closing",InputFileName);
	}
	free(BackFileName);
	return nerrs;
}