/*************************************************************************
 * RootPath -- Convert a pathname  argument  to  root  based  cannonical *
 *             form.													 *
 * Author:     Don A. Williams											 *
 *             CompuServ -												 *
 *             Genie     - DON-WILL										 *
 *																		 *
 * RootPath determines the current directory,  appends the path argument *
 * (which may affect which disk the current directory is  relative  to), *
 * and  qualifies  "."  and  ".." references.  The result is a complete, *
 * simple, path name with drive specifier.  							 *
 *																		 *
 * If the relative path the user specifies  does  not  include  a  drive *
 * spec., the default drive will be used as the base. (The default drive *
 * will never be changed.) 												 *
 *																		 *
 *     entry:  RelativePath -- pointer to the pathname to be expanded.   *
 *             FullPath -- must point to a working buffer, see warning.	 *
 *            															 *
 *     exit:   FullPath -- the full path which results.					 *
 *																		 *
 *     return: A pointer to FullPath if OK, NULL if an error occurs.
 *																		 *
 *     calls:  getcurdir getdisk										 *
 *																		 *
 *     warning: FullPath  must point to a working buffer large enough to *
 *              hold the longest possible relative  path  argument  plus *
 *              the longest possible current directory path.  			 *
 *																		 *
 * RootPath  was  modeled after the public domain file "rootpath.c" with *
 * fairly extensive "enhancement".  The major enhancement  is  provision *
 * for  relative  paths  such  as  "..\..\here"  which  MS-DOS  does NOT *
 * support.  I found that such  a  construct  would  be  very  handy  in *
 * several  of  my uses of UFIND so I added it.  Provision has also been *
 * made to handle either of the two element name  separator  characters; *
 * the '\' of MS-DOS or the '/' of Unix.  The MS-DOS facilities actually *
 * recognize  either  separator  at  the programmatic level but too many *
 * MS-DOS programs do NOT.												 *
 *																		 *
 ************************************************************************/

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int             GetCurrentDirectory(int Disk, char *CurDir);

 char           *
RootPath (char *CurDir, char *RelPath, char *FullPath) {
	char           *p, *p1, *p2;

	if (RelPath[0] == '\0') {
		FullPath[0] = '\0';
		return (NULL);
		}
	if (RelPath[1] == ':') {	/* Path contains drive	 */
		FullPath[0] = RelPath[0];
		FullPath[1] = RelPath[1];
		memmove(RelPath, RelPath + 2, strlen(RelPath) + 1);
		}
	else {
		FullPath[0] = CurDir[0];
		FullPath[1] = CurDir[1];
		}
	FullPath[2] = '\0';

	if (strlen(RelPath) == 2 && *(RelPath + 1) == ':') strcat(RelPath, "\\");
	if ((p = strchr("\\/", *RelPath)) != NULL) strcpy(FullPath + 2, RelPath);
	else {
		FullPath[2] = '\\';
		if (FullPath[0] != CurDir[0]) {
			if (GetCurrentDirectory((int) (toupper(*FullPath) - '@'), &FullPath[3]))
				return (NULL);
			}
		else {
			strcpy(FullPath, CurDir);
			FullPath[strlen(FullPath) - 1] = '\0';
			}
		p = RelPath;
		while (1) {
			p1 = strchr(p, '\\');
			if (!strncmp(p, "..", 2)) {
				if ((p2 = strrchr(FullPath, '\\')) != NULL) *p2 = '\0';
				p = p1 + 1;
				}
			else if (!strncmp(p, ".", 1)) {
				p = p1 + 1;
				break;
				};
			if (p1 == NULL) break;
			}
		if ((strlen(FullPath) > 3) || (strlen(FullPath) == 2))
			strcat(FullPath, "\\");
		strcat(FullPath, p);
		}

	while ((p = strchr(FullPath, '/')) != NULL) *p++ = '\\';

	if ((strlen(FullPath) == 3) && (FullPath[2] == '\\'))
		FullPath[2] = '\0';
	return (strlwr(FullPath));
	}