@echo off
REM PathSubs.bat - Compact the PATH statement by using SUBST for the paths in
REM                the list.  Also allow to add or delete a path.  See the
REM                Instructions() function for a description of how to use

subst | cenvi %0.bat %1 %2 %3 %4 %5 %6 %7 %8 %9
GOTO CENVI_EXIT

Instructions()
{
   printf("\a\n")
   printf("PathSubs - Keep the PATH environment variable as short as possible buy using\n")
   printf("           DOS's SUBST command to replace PATH directories with drive letters.\n")
   printf("\n")
   printf("SYNTAX:  PathSubs [ < + | - > d:\\path ]\n")
   printf("\n")
   printf("Where:  +        Add a path to the PATH variable, if not already there.\n")
   printf("        -        Remove a path from the PATH variable, if it is there.\n")
   printf("        d:\\path  The FULL directory to add or remove from PATH.\n")
   printf("\n")
   printf("The following table shows examples of the SUBST command.\n");
   printf("\n")
   printf("PathSubs            Compacts the current path using drive substitutions\n")
   printf("PathSubs + D:\\UTL   Add D:\UTL to the current PATH\n")
   printf("PathSubs - D:\\UTL   Remove D:\UTL from the current PATH\n")
   printf("\n")
}

// The following code uses the path structure which has the elements:
//   Count      : number of directories in the path
//   path[Count].Dir   : array of Count strings, each containing a full directory
//   path[Count].Drive : drive letter substituted here, else 0 for not subst
// and also the Subs structure which has the elements
//   Count        : number of drives Substituted
//   sub[Count].Drive : array of Count drive letters substituted for Dir
//   sub[Count].Dir   : array of Count strings for the path of each substituted driev

main(ArgCount,ArgStrings)
{
   // Decide what to do from input
   if ( ArgCount == 3 ) {
      Command = ArgStrings[1]
      CommandPath = ArgStrings[2]
      if ( Command[1] != 0  || ( Command[0] != '+'  &&  Command[0] != '-' ) ) {
         // Invalid input, so just show how to use and quit
         Instructions()
         return(1)
      }
   } else if ( ArgCount != 1 ) {
      // Invalid input, so just show how to use and quit
      Instructions()
      return(1)
   }
   // Build lists of substituted drives and of paths
   Subs = BuildSubsArray()
   Paths = SeparatePATHIntoDirs(Subs)
   // implement new command based on input arguments
   if ( ArgCount == 3 ) {
      if ( Command[0] == '+' )
         AddPath(CommandPath,Paths)
      else
         RemovePath(CommandPath,Paths,Subs)
   }
   CompactPaths(Paths,Subs)
   ShowCurrentPath(Paths)
   return(0)
}

ShowCurrentPath(p)
{
   printf("PATH=")
   for ( i = 0, count = 0; i < p.Count; i++ ) {
      if ( p.path[i].Dir != NULL ) {
         if ( count++ ) printf(";")
         printf("%s",p.path[i].Dir)
      }
   }
   printf("\n")
}

AddPath(Dir,p)
{
   // First check if this directory is already in the path
   for ( i = 0; i < p.Count; i++ ) {
      if ( 0 == stricmp(Dir,p.path[i].Dir) ) {
         printf("Directory \"%s\" is already in the PATH\n",p.path[i].Dir)
         return
      }
   }
   // was not found above in the path, and so add to end of path list
   strcpy(p.path[p.Count].Dir,Dir)
   p.path[p.Count].Drive = 0  // assume it is not substituted
   p.Count++
}

RemovePath(Dir,p,s)
{
   // First check that this directory is already in the path
   for ( i = 0; i < p.Count; i++ ) {
      if ( 0 == stricmp(Dir,p.path[i].Dir) ) {
         break
      }
   }
   if ( i == p.Count )
      printf("Directory \"%s\" is not in the PATH\n",Dir)
   else {
      // remove this directory from the path, and remove its SUBST
      if ( (drive = toupper(p.path[i].Drive)) != 0 ) {
         // this path has a SUBSTITUTED drive, and so remove that subst drive
         for ( j = 0; j < s.Count; j++ ) {
            if ( s.sub[j].Drive == drive )
               break;
         }
         s.sub[j].Drive = 0;
         // use DOS's SUBST utility to un-substitute this drive
         system("SUBST %c: /D",drive)
      }
      // set path structure to know this path is no longer there
      p.path[i].Drive = 0;
      p.path[i].Dir = NULL
   }
}

BuildSubsArray()  // Subst output was piped to this program, and so use that output
                  // to build list of substituted drives and paths they point to.
                  // output line is of the form "G: is substituted for C:\OS2"
{
   for ( s.Count = 0; NULL != (line=gets()); s.Count++ ) {
      // first letter of SUBST is the drive letter
      s.sub[s.Count].Drive = toupper(line[0]);
      // last string before whitespace is the path
      for ( d = line + strlen(line); d[-1] != ' '; d-- ) ;
      strcpy(s.sub[s.Count].Dir,d)
   }
   return(s)
}


SeparatePATHIntoDirs(subs) // Separate the PATH environment variable into
                           // individual paths, return element Count to how many
                           // paths, and setting each Dir[] element to a path.
                           // any paths that fit into the subst array will be
                           // replaced by their full subst path
{
   Paths.Count = 0
   p = PATH
   while ( NULL != p  &&  0 != p[0] ) {
      if ( ';' == p[0] )
         p++   // skip semi-colons
      else {
         strcpy(NewDir,p)
         if ( NULL != (c = strchr(NewDir,';')) )
            c[0] = 0;
         // check if this is a "A:\" type path and if it is substituted
         Paths.path[Paths.Count].Drive = 0   // assume it is not substituted
         if ( 0 == strcmp(NewDir+1,":\\") ) {
            // loop through subst to see if this is one of those
            for ( i = 0; i < subs.Count; i++ ) {
               if ( toupper(NewDir[0]) == subs.sub[i].Drive ) {
                  // put in the real path for this substituted one
                  NewDir = subs.sub[i].Dir
                  Paths.path[Paths.Count].Drive = subs.sub[i].Drive
                  break
               }
            }
         }
         strcpy(Paths.path[Paths.Count++].Dir,NewDir)
         p = strchr(p,';')
      }
   }
   return(Paths)
}

CompactPaths(p,s) // this writes the PATH statement in compacted form, substituting
                  // all drives for a path whenever it can.  It assumes that it will
                  // Subst on any drive letter that isn't used already.
{
   TempPath[0] = '\0'  // restart directories from scratch
   SubstDir = "A:\\" // template for what a subdir looks like
   for ( i = 0; i < p.Count; i++ ) {
      if ( p.path[i].Dir != NULL ) {
         if ( p.path[i].Drive != 0 ) {
            // this path already has a drive letter substituted, and so keep it
            SubstDir[0] = p.path[i].Drive
            strcat(TempPath,SubstDir)
         } else if ( strlen(p.path[i].dir) <= 3 ) {
            // path can't get any shorter by substituting, and so keep it as it is
               strcat(TempPath,p.path[i].Dir)
         } else {
            // get the next drive letter for substituting
            drive = NextFreeDrive()
            if ( drive != 0 ) {
               // create a new SUBST drive for this path
               system("SUBST %c: %s",drive,p.path[i].Dir)
               SubstDir[0] = p.path[i].Drive = drive
               strcat(TempPath,SubstDir)
               // add this new drive to list of substituted drives
               strcpy(s.sub[s.Count].Dir,p.path[i].Dir)
               s.sub[s.Count].Drive = drive
               s.Count++
            } else {
               // there are no more available free drives, and so simply add this dir
               strcat(TempPath,p.path[i].Dir)
            }
         }
         strcat(TempPath,";")
      }
   }
   // remove the final semi-colon
   TempPath[strlen(TempPath)-1] = 0
   PATH=TempPath
}

NextSubstDrive = 'D'    // this global is incremented for each drive to test

NextFreeDrive() // return a character for the next available free drive letter
                // or '\0' if no drive available. Check if a drive is available
                // by seeing if there's a current path for that drive
{
   CurDir = "C:."  // this string, with drive letter substituted tested for curdir
   while ( NextSubstDrive <= 'Z' ) {
      CurDir[0] = NextSubstDrive++
      if ( NULL == FullPath(CurDir) ) {
         return( NextSubstDrive - 1 )
      }
   }
   // no free drive was found; indicate by returning 0
   return '\0'
}

:CENVI_EXIT