#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>

int link_file(char *, char *);

int force = 0; /* -f flag */
int do_symlink = 0; /* -s flag */
int follow_link = 0; /* -L/-P flag */

int main(int argc, char * argv[]) {
  int file_start = 1;
  int source_count = 0;
  char * path_dir;
  char * ln_name;

  if(argc < 3) {
    fprintf(stderr, "%s: missing file operand\n", argv[0]);
    exit(1);
  }

  if(strcmp(argv[file_start], "-L") == 0) {
    follow_link = AT_SYMLINK_FOLLOW;
    file_start++;
  }
  else if(strcmp(argv[file_start], "-P") == 0) {
    follow_link = 0;
    file_start++;
  }

  if(strcmp(argv[file_start], "-f") == 0) {
    force = 1;
    file_start++;
  }
  else if(strcmp(argv[file_start], "-s") == 0) {
    do_symlink = 1;
    file_start++;
  }
  else if(strcmp(argv[file_start], "-fs") == 0
	  || strcmp(argv[file_start], "-sf") == 0) {
    force = 1;
    do_symlink = 1;
    file_start++;
  }

  if(strcmp(argv[file_start], "-L") == 0) {
    follow_link = AT_SYMLINK_FOLLOW;
    file_start++;
  }
  else if(strcmp(argv[file_start], "-P") == 0) {
    follow_link = 0;
    file_start++;
  }

  if((argc - file_start) < 2) {
    fprintf(stderr, "%s: missing file operand\n", argv[0]);
    exit(1);
  }

  source_count = argc - (file_start + 1);

  if(source_count == 1) {
    int ret = link_file(argv[file_start], argv[file_start+1]);
    if(ret == 1) {
      fprintf(stderr, "%s: failed to create link '%s': File exists\n",
	    argv[0], argv[file_start + 1]);
      exit(1);
    }
    return 0;
  }
  else {
    path_dir = argv[argc - 1];
    for(int i = file_start; i < (argc - 1); i++) {
      int length = strlen(path_dir);
      length += strlen(argv[i]);
      ln_name = calloc(length + 2, sizeof(*ln_name));
      strcpy(ln_name, path_dir);
      strcat(ln_name, "/");
      strcat(ln_name, argv[i]);
      int ret = link_file(argv[i], ln_name);
      if(ret == 1) {
	fprintf(stderr, "%s: failed to create link '%s': File exists\n",
		argv[0], ln_name);
        exit(1);
      }
      free(ln_name);
    }
  }
}

int link_file(char * source, char * dest) {
  struct stat buf;
  lstat(source, &buf);
  if(strcmp(source, dest) == 0 && !force) {
    return 1;
  }
  else if(access(dest, F_OK) != -1 && !force) {
    return 1;
  }
  else if(access(dest, F_OK) != -1 && force) {
    unlink(dest);
  }

  if(do_symlink) {
    return symlink(source, dest);
  }
  else if(S_ISLNK(buf.st_mode)) {
    return linkat(AT_FDCWD, source, AT_FDCWD, dest, follow_link);
  }
  else {
    return link(source, dest);
  }
}