#include <limits.h>

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <unistd.h>

#include <errno.h>

/* Needed for execve */

extern char **environ;

int main( int argc,

          char** argv )

{

  char *fullname;   /* 'fullname' is used to store the absolute path to the

                       tool being executed; it serves as a base to compute

                       the realname of that tool, and the directory holding

                       our runtime libraries */

  char *realname;   /* 'realname' is the real name of the tool, that is what

                       the wrapper is currently impersonating */

  char *basedir;    /* 'libdir' contains our runtime libraries */

  char *lastslash;  /* Temporary variables now */

  char *ldlibpath;

  size_t len;

  int execve_ret;

  /* In case we have a relative or absolute pathname (ie. contains a slash),

   * then realpath wll work. But if the tool was found in the PATH, realpath

   * won't work, and we'll have to search ourselves.

   * This if{}else{} block allocates memory for fullname. */

  if( strchr( argv[0], '/' ) ) {

    fullname = (char*) malloc( PATH_MAX * sizeof(char) );

    if( ! realpath( argv[0], fullname ) ) {

      perror( "tool wrapper" );

      exit( 1 );

    }

  } else {

    char *path;

    char *mypath;

    char *colon;

    char *testname;

    struct stat st;

    fullname = NULL;

    colon = mypath = path = strdup( getenv( "PATH" ) );

    while( colon ) {

      colon = strchr( mypath, ':' );

      if( colon ) {

        *colon = '\0';

      }

      testname = strdup( mypath );

      testname = (char*) realloc( testname,   strlen( testname )

                                            + strlen( argv[0] )

                                            + 2 * sizeof(char) );

      memset( testname + strlen( testname ),

              0,

              strlen( argv[0] ) + 2 * sizeof(char) );

      strcat( testname, "/" );

      strcat( testname, argv[0] );

      if( stat( testname, &st ) == 0 ) {

        /* OK, exists. Is it a regular file, or a

         * symlink, which the current user may execute? */

        if( S_ISREG( st.st_mode ) && ! access( testname, X_OK || R_OK ) ) {

          fullname = strdup( testname );

          break;

        }

      }

      free( testname );

      mypath = colon + 1;

    }

    free( path );

    if( ! fullname ) {

      fprintf( stderr, "tool wrapper: %s: command not found\n", argv[0] );

      exit( 1 );

    }

  }

  /* Duplicate my own name to add the 'dot' to tool name */

  realname = strdup( fullname );

  realname = (char*) realloc( realname, strlen( realname) + 2 * sizeof(char) );

  realname[ strlen( realname ) + 1 ] = '\0';

  /* Add the dot after the last '/' */

  lastslash = strrchr( realname, '/' );

  memmove( lastslash + 1, lastslash, strlen( lastslash ) );

  *( lastslash + 1 ) = '.';

  /* Compute the basedir of the tool */

  basedir = strdup( fullname );

  lastslash = strrchr( basedir, '/' );

  *lastslash = '\0';

  lastslash = strrchr( basedir, '/' );

  *lastslash = '\0';

  /* Append '/lib' */

  len = strlen( basedir );

  basedir = (char*) realloc( basedir, len + 5 );

  *( basedir + len ) = '\0';

  strcat( basedir, "/lib" );

  /* Now add the directory with our runtime libraries to the

     front of the library search path, LD_LIBRARY_PATH */

  ldlibpath = getenv( "LD_LIBRARY_PATH" );

  if( ldlibpath ) {

    basedir = (char*) realloc( basedir,   strlen( basedir )

                                        + strlen( ldlibpath )

                                        + 2 * sizeof(char) );

    strcat( basedir, ":" );

    strcat( basedir, ldlibpath );

  }

  if( setenv( "LD_LIBRARY_PATH", basedir, 1 ) ) {

    errno = ENOMEM;

    perror( "tool wrapper" );

    exit( 1 );

  }

  /* Execute the real tool, now */

  execve_ret = execve( realname, argv, environ );

  /* In case something went wrong above, print a

     diagnostic message, and exit with error code 1 */

  perror( "tool wrapper" );

  return 1;

}