/****************************************
*  Computer Algebra System SINGULAR     *
****************************************/
/* $id:$ */

/* find_exec.c -- Find a program, given an argv[0]
   Copyright (C) 1996 Free Software Foundation, Inc.
   Copyright (C) 1990 by W. Wilson Ho.
   This file is part of the GNU Dld Library. */

/* Adapted for use with Singular by obachman@mathematik.uni-kl.de  4/98*/

#include "mod2.h"

#if ! defined(MSDOS) && ! defined(__MWERKS__)

#include <unistd.h> /* always defiend */
#include <stdlib.h>
#include <string.h>

#if !defined(ESINGULAR) && !defined(TSINGULAR)
#include "mmemory.h"
#endif


#ifndef MAXPATHLEN
#define MAXPATHLEN 1024
#endif

/* Do not return copies of sth, but simply the strings
   -- we make copies later */
#define copy_of(string) mstrdup(string)

/* ABSOLUTE_FILENAME_P (fname): True if fname is an absolute filename */
#ifdef atarist
#define ABSOLUTE_FILENAME_P(fname)        ((fname[0] == '/') || \
        (fname[0] && (fname[1] == ':')))
#else
#define ABSOLUTE_FILENAME_P(fname)        (fname[0] == '/')
#endif /* atarist */

/* Return the absolute name of the program named NAME.  This function
   searches the directories in the PATH environment variable if PROG
   has no directory components. */
#ifndef HAVE_READLINK
char * find_executable (const char *name)
#else
char * find_executable_link (const char *name)
#endif
{
  char *search;
  char *p;
#ifdef WINNT
  char *extra = NULL;
#endif
  char tbuf[MAXPATHLEN];

  if (ABSOLUTE_FILENAME_P(name))
  {
      /* If we can execute the named file then return it. */
      if (! access (name, X_OK))
        return copy_of (name);
  }
  else
  {
    if (((name[0] == '.') && (name[1] == '/')) ||
        ((name[0] == '.') && (name[1] == '.') && (name[2] == '/')) ||
        strchr(name, '/') != NULL)
    {

#ifdef HAVE_GETCWD
      getcwd (tbuf, MAXPATHLEN);
#else
# ifdef HAVE_GETWD
      getwd (tbuf);
# endif
#endif
      strcat (tbuf, "/");
      strcat (tbuf, name);
      if (! access(name, X_OK))
        return copy_of (tbuf);
    }

    search = getenv("PATH");
/* for winnt under msdos, cwd is implictly in the path */
#ifdef WINNT
    p = getenv("SHELL");
    if (p == NULL || strlen(p) < 2)
    {
      /* we are under msdos display */
      extra = (char*) AllocL((search != NULL ? strlen(search) : 0) + 3);
      strcpy(extra, ".:");
      if (search != NULL) strcat(extra, search);
      search = extra;
    }
#endif
    p = search;

    if (p != NULL)
    {
      while (1)
      {
        char *next;
        next = tbuf;

        /* Copy directory name into [tbuf]. */
        /* This is somewhat tricky: empty names mean cwd, w.r.t. some
           shell spec */
        while (*p && *p != ':')
          *next ++ = *p ++;
        *next = '\0';

        if ((tbuf[0] == '.' && tbuf[1] == '\0') || tbuf[0] == '\0') {
#ifdef HAVE_GETCWD
          getcwd (tbuf, MAXPATHLEN);
#else
# ifdef HAVE_GETWD
          getwd (tbuf);
# endif
#endif
        }

        if (tbuf[strlen(tbuf)-1] != '/') strcat(tbuf, "/");
        strcat (tbuf, name);
        
        /* If we can execute the named file, then return it. */
        if (! access (tbuf, X_OK))
        {
#ifdef WINNT
          if (extra != NULL)
            FreeL(extra);
#endif
          return copy_of (tbuf);
        }

        if (*p != '\0')
        {
          p ++;
        }
        else
        {
          break;
        }

      }
    }
  }

  return NULL;
}

#ifdef HAVE_READLINK

/* similar to readlink, but dont' mess up absolute pathnames */
int my_readlink(const char* name, char* buf, size_t bufsize)
{
  char buf2[MAXPATHLEN];
  int ret;
  
  if ((ret = readlink(name, buf2, bufsize)) > 0)
  {
    buf2[ret] = 0;
    if (*name == '/' && *buf2 != '/')
    {
      char* last = strrchr(name, '/');
      int i = 0;
      while (&(name[i]) != last)
      {
        buf[i] = name[i];
        i++;
      }
      buf[i] = '/';
      i++;
      strcpy(&(buf[i]), buf2);
      return i + ret;
    }
    else
    {
      strcpy(buf, buf2);
    }
  }
  return ret;
}

#define MAX_LINK_LEVEL 10
/* similar to readlink (cf. man readlink), except that symbolic links are 
   followed up to MAX_LINK_LEVEL
*/

int full_readlink(const char* name, char* buf, size_t bufsize)
{
  int ret;
  
  if ((ret=my_readlink(name, buf, bufsize)) > 0)
  {
    char buf2[MAXPATHLEN];
    int ret2, i = 0;
    
    do
    {
      buf[ret] = '\0';
      if ((ret2 = my_readlink(buf, buf2, MAXPATHLEN)) > 0)
      {
        i++;
        buf2[ret2] = '\0';
        strcpy(buf, buf2);
        ret = ret2;
      }
      else
      {
        return ret;
      }
    }
    while (i<MAX_LINK_LEVEL);
  }
  return -1;
}
  
  
char * find_executable (const char *name)
{
  char * link = find_executable_link(name);
  char buf[MAXPATHLEN];
  int ret;

  if (link == NULL && (ret=full_readlink(name, buf, MAXPATHLEN)) > 0)
  {
    buf[ret] ='\0';
    link = find_executable_link(buf);
  }
  if (link != NULL && (ret=full_readlink(link, buf, MAXPATHLEN)) > 0)
  {
    char *p = strrchr(link, '/');
    char *executable;


    if(p!=NULL) *(p+1)='\0';
    buf[ret]='\0';

    if (buf[0] != '/')
    {
      executable = (char*) AllocL(strlen(link) + ret + 1);
      strcpy(executable, link);
      strcat(executable, buf);
    }
    else
    {
      executable = copy_of(buf);
    }

    FreeL(link);
    return executable;
  }

  return link;
}
#endif /* HAVE_READLINK */

#else

char* find_executable (const char *name)
{
  return NULL;
}

#endif /* #if ! defined(MSDOS) && ! defined(__MWERKS__) && defined(HAVE_SYS_TYPES_H) && defined(HAVE_PWD_H)&&defined(HAVE_SYS_PARAM_H) */