/*----------------------------------------------------------------------------
                                 libopt
------------------------------------------------------------------------------
  This is a program to convert link library filepaths to linker options
  that select them.  E.g. ../pbm/libpbm.so becomes -L../pbm -lpbm   .

  Each argument is a library filepath.  The option string to identify
  all of those library filepaths goes to Standard Output.

  If an argument doesn't make sense as a library filespec, it is
  copied verbatim, blank delimited, to the output string.
  
  There is no newline or null character or anything after the output.
------------------------------------------------------------------------------
  Why would you want to use this?  

  On some systems, the -L/-l output of this program has exactly the
  same effect as the filepath input when used in the arguments to a
  link command.  A GNU/Linux system, for example.  On others (Solaris,
  for example), if you include /tmp/lib/libpbm.so in the link as a
  link object, the executable gets built in such a way that the system
  accesses the shared library /tmp/lib/libpbm.so at run time.  On the
  other hand, if you instead put the options -L/tmp/lib -lpbm on the
  link command, the executable gets built so that the system accesses
  libpbm.so in its actual installed directory at runtime (that
  location might be determined by a --rpath linker option or a
  LD_LIBRARY_PATH environment variable at run time).

  In a make file, it is nice to use the same variable as the
  dependency of rule that builds an executable and as the thing that
  the rule's command uses to identify its input.  Here is an example
  of using libopt for that:

     PBMLIB=../pbm/libpbm.so
     ...
     pbmmake: pbmmake.o $(PBMLIB)
             ld -o pbmmake pbmmake.o `libopt $(PBMLIB)` --rpath=/lib/netpbm

  Caveat: "-L../pbm -lpbm" is NOT exactly the same as "libpbm.so" on any
  system.  All of the -l libraries are searched for in all of the -L
  directories.  So you just might get a different library with the -L/-l
  version than if you specify the library file explicitly.

-----------------------------------------------------------------------------*/
#define _BSD_SOURCE 1
    /* Make sure strdup() is in stdio.h */

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

typedef unsigned char bool;
#define true (1)
#define false (0)

static void
parse_filename(const char * const filename,
               char ** const libname_p,
               bool * const valid_library_p) {
/*----------------------------------------------------------------------------
   Extract the library name component of the filename 'filename'.  This
   is just a filename, not a whole pathname.

   Return it in newly malloc'ed storage pointed to by '*libname_p'.
   
   E.g. for "libxyz.so", return "xyz".

   return *valid_library == true iff 'filename' validly names a library
   that can be expressed in a -l linker option.
-----------------------------------------------------------------------------*/
    char *lastdot;  
    /* Pointer to last period in 'filename'.  Null if none */
    
    /* We accept any period-delimited suffix as a library type suffix.
           It's probably .so or .a, but is could be .kalamazoo for all we
           care.  
        */
    lastdot = strrchr(filename, '.');
    if (lastdot == NULL) {
        /* This filename doesn't have any suffix, so we don't understand
           it as a library filename.
           */
        *valid_library_p = false;
    } else {
        if (strncmp(filename, "lib", 3) != 0) {
            /* This filename doesn't start with "lib", so we can't express
               it as a -l option.
            */
            *valid_library_p = false;
        } else {
            /* Extract everything between "lib" and "." as 
                   the library name 
                */
            *libname_p = strdup(filename+3);
            (*libname_p)[lastdot - filename - 3] = '\0';
        
            if (strlen(*libname_p) == 0)
                *valid_library_p = false;
            else
                *valid_library_p = true;
        }
    }
}   



static void
parse_filepath(const char * const filepath,
               char ** const directory_p, char ** const filename_p) {
/*----------------------------------------------------------------------------
   Extract the directory and filename components of the filepath 
   'filepath' and return them in newly malloc'ed storage pointed to by
   '*directory_p' and '*filename_p'.
-----------------------------------------------------------------------------*/
    char *lastslash; /* Pointer to last slash in 'filepath', or null if none */

    lastslash = strrchr(filepath, '/');

    if (lastslash == NULL) {
        /* There's no directory component; the filename starts at the
           beginning of the filepath 
        */
        *filename_p = strdup(filepath);
        *directory_p = strdup("");
    } else {
        /* Split the string at the slash we just found, into filename and 
           directory 
           */
        *filename_p = strdup(lastslash+1);
        *directory_p = strdup(filepath);
        (*directory_p)[lastslash - filepath] = '\0';
    }
}



int
main(int argc, char **argv) {

    unsigned int arg;  /* Index into argv[] of argument we're processing */

    for (arg = 1; arg < argc; arg++) {
        const char *filepath;  /* The argument we're processing */
        bool valid_library;  
          /* Our argument is a valid library filepath that can be converted to
             -l/-L notation.
          */
        char *directory;
          /* Directory component of 'filepath' */
        char *filename;
          /* Filename component of 'filepath' */
        char *libname;
          /* Library name component of 'filename'.  e.g. xyz in libxyz.so */

        filepath = argv[arg];

        parse_filepath(filepath, &directory, &filename);

        parse_filename(filename, &libname, &valid_library);

        if (valid_library) {
            if (strlen(directory) == 0)
                fprintf(stdout, "-L. -l%s ", libname);
            else
                fprintf(stdout, "-L%s -l%s ", directory, libname);
        } else
            fprintf(stdout, "%s ", filepath);
    
        free(directory); free(filename); free(libname);
    }
    return 0;
}