/*
 *                            COPYRIGHT (C) 2000 BY
 *                      COMPAQ COMPUTER CORPORATION, HOUSTON
 *                       TEXAS.  ALL RIGHTS RESERVED.
 *
 *    THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY BE USED AND COPIED
 *    ONLY IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND WITH THE INCLUSION
 *    OF THE ABOVE COPYRIGHT NOTICE.  THIS SOFTWARE OR ANY OTHER COPIES
 *    THEREOF MAY NOT BE PROVIDED OR OTHERWISE MADE AVAILABLE TO ANY OTHER
 *    PERSON.  NO TITLE TO AND OWNERSHIP OF THE SOFTWARE IS HEREBY TRANSFERRED.
 *
 *    THE INFORMATION IN THIS SOFTWARE IS SUBJECT TO CHANGE WITHOUT NOTICE AND
 *    SHOULD NOT BE CONSTRUED AS A COMMITMENT BY COMPAQ COMPUTER CORPORATION.
 *
 *    COMPAQ ASSUMES NO RESPONSIBILITY FOR THE USE OR RELIABILITY OF ITS
 *    SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY COMPAQ.
 *
 *    NO RESPONSIBILITY IS ASSUMED FOR THE USE OR RELIABILITY OF SOFTWARE
 *    ON EQUIPMENT THAT IS NOT SUPPLIED BY COMPAQ COMPUTER CORPORATION.
 *
 *    SUPPORT FOR THIS SOFTWARE IS NOT COVERED UNDER ANY COMPAQ SOFTWARE
 *    PRODUCT SUPPORT CONTRACT, BUT MAY BE PROVIDED UNDER THE TERMS OF THE
 *    CONSULTING AGREEMENT UNDER WHICH THIS SOFTWARE WAS DEVELOPED.
 *
 */
/*
 *    This code shows a way to simulate the UNIX 'ls' command (no
 *    options) using opendir, readdir and closedir. These functions are
 *    available starting from OpenVMS V7.0.
 *    
 *    
 *    PROGRAM NOTES:
 *    
 *    Before activating the program, perform the following:
 *    
 *    VMS information:
 *    ---------------
 *    
 *         $ cc/define=(COLUMNS=x) ls
 *         with 0<x<=4
 *         $ link ls
 *    
 *    Foreign symbol definition:
 *    
 *         $ ls :== $disk:[directory]ls.exe
 *    
 *    Tru64 UNIX information:
 *    ----------------------
 *    
 *         % cc -o ls -DCOLUMNS=x -lcurses ls.c
 *         with 0<x<=4
 *    
 *    Both systems:
 *    ------------
 *    The syntax for activating the program:
 *    
 *         ($) (%) ls [directory]
 *    
 *    The directory is optional and defaults to the current directory
 *    
 *         (. in unix-style)
 *    
 *    On OpenVMS, if the directory name is entered in VMS format, the file
 *    names display is in VMS format; if the directory name is entered in
 *    Unix-format, the file names display is in Unix-style format.
 *    
 */
#define _BSD44_CURSES
#include <sys/types.h>
#include <dirent.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <curses.h>

#pragma message fatal errormessage
#ifndef COLUMNS
#define COLUMNS 4
#elif (COLUMNS <= 0)
#error COLUMNS must be greater than 0.
#elif (COLUMNS > 4)
#undef COLUMNS
#define COLUMNS 4
#endif

#define MAX_PATH 256
#define DEFAULT_SCREEN_WIDTH 80

int main(int argc, char **argv){
 DIR *ThisDir;
 struct dirent *DirEntry;
 char *filenames;
 char *DirName = ".";
 int i,NumberSpaces;
 char *cp;
 unsigned int columns, MaxCol;
 char ColumnsDetermined;

 /*
  * if no argument given, default it to the current directory.
  */
 if (argc == 2)
     DirName = argv[1];

 /*
  * Init curses. The fact that _BSD44_CURSES is defined will prevent
  * a clear screen caused by initscr(). We need it so that COLS is
  * defined to the proper screen width.
  */
 initscr();

 /*
  * Compute MaxCol. For a screen width of 80, we should divide into COLUMNS.
  * COLS is a predefined variable within curses.
  */
 MaxCol = (COLUMNS * COLS) / DEFAULT_SCREEN_WIDTH;

 /*
  * Allocate space for filenames.
  */
 filenames = calloc(sizeof(char),COLS+1);

 /*
  * Open the directory stream.
  */
 ThisDir = opendir(DirName);
 if (!ThisDir){
     perror("opendir error");
     exit(-1);
 }
 /*
  * Loop on each entry until DirEntry is equal to NULL.
  */
 while((DirEntry = readdir(ThisDir)) != NULL){

       /*
        * Determine the column number for this file.
        */
       columns = 1;
       ColumnsDetermined = 0;
       while (!ColumnsDetermined){
              if (strlen(DirEntry->d_name) <
                        columns*COLS/MaxCol)
                  ColumnsDetermined++;
              else
                  columns++;
       }

       /*
        * Make some chanity check. This will abort if asumption is false.
        */
       assert(columns <= MaxCol);

       /*
        * determine the number of spaces.
        */
       NumberSpaces = 0;
       for(i=0; i< columns;i++)
           NumberSpaces += COLS/MaxCol;

       /*
        * If the number of spaces does not fit into the line,
        * print out the line.
        */
       if (strlen(filenames) + NumberSpaces > COLS){
           printf("%s\r\n",filenames);
           filenames[0] = '\0';
       }

       /*
        * Adjust the number of spaces.
        */
       NumberSpaces -= strlen(DirEntry->d_name);

       /*
        * Add entry to line.
        */
       strcat(filenames,DirEntry->d_name);

       /*
        * Padd the line with the computed number of spaces.
        */
       cp=filenames + strlen(filenames);
       for (i=0;i<NumberSpaces ;i++)
            *cp++ = ' ';
       *cp = '\0';
 }

 /*
  * Display the last line and close the directory stream.
  */
 printf ("%s\r\n",filenames);

 /*
  * Close Directory stream.
  */
 closedir(ThisDir);

 /*
  * Finally return to shell.
  */
 return 1;
}