/* filestuff.c
 * Authors: Pete Broadwell
 *          Josh Vickery
 * this program contains functions for reading a list from a file, 
 * and for printing a list to a file or to an output stream. 
 */

#include "ll_defs.h"

/* read a list from a file, return a pointer to a linked list 
/* this fuction is called from within the main interactive loop 
 * of fun_with_lists and requires that it be passed the name of
 * the file to be opened.
 */

llist *readfile(char *file) {
  /* variable declarations */
  FILE *fd;
  char buf[256];
  int len; 
  node *current_node;
  llist *current_list;
  
  /* try to open the file, exit on failure */
  fd=fopen(file, "r");
  if (fd == NULL) {
    printf("Filename does not exist.\n");
    exit(1);
  }
  
  /* read the first line of the buffer into a new node */
  if (fgets(buf, sizeof(buf), fd) == NULL)
    printf("Unable to read from file.\n");
  len=strlen(buf);
  buf[len-1]='\0'; 
  current_node=(node *) create_n(buf);
  
  /* create a new linked list, with this node as the first, last and cursor */
  current_list=(llist *) create_l(current_node);

  /* add the remaining lines in the file to the list */
  while (fgets(buf, sizeof(buf), fd) != NULL) {
    len=strlen(buf);
    buf[len-1]='\0'; 
    current_node=(node *) create_n(buf);  
    current_list=(llist *)add_to_end(current_list, current_node);
  }

  return(current_list);
}

/* write a list to a file or the screen, take a file pointer and llist 
 * pointer.  Since this can take standard out, the file must be open 
 * This function is called from the main loop of fun_with_lists
 */

writefile(FILE *fp, llist *clist) {

  /* this line checks, among other things, that we're not trying to print
   * a list on which all elments have been deleted (because in this
   * implementation, such a list still contains one element, which is
   * NULL, but you obviously can't print that out.
   */
  if ((clist!=NULL) && ((clist->first!=NULL) && (clist->last!=NULL))) {
    
    /* move the cursor to the front of the list */ 
    clist->current=(node *)tofront(clist);
    /* step through the list and print each element */
    while (clist->current != clist->last) {
      fprintf(fp, "%s\n", clist->current->contents); 
      clist->current = (node *)advance_cursor(clist);  
    }
    
    fprintf(fp, "%s\n", clist->current->contents);
    
    clist->current=(node *)tofront(clist);
    
  }
}