#include "ilist_destructive.h"
#include <stdlib.h>


// The ilist ADT is a pointer to this secret struct
struct ilist_ADT {
   struct ilist_ADT * rest;
   int first;
   int length;
};


// returns an empty ilist
ilist iempty(){
   return NULL;
}


// returns 1 if the ilist is empty, 0 if it is not
int iempty_huh(ilist il){
   if (il == iempty()) {
      return 1;
   }
   else return 0;
}


// reutrns the first element in an ilist
// ilist should not be empty
int ifirst(ilist il){
    return il->first;
}


// icons creates a new node
ilist icons(int in, ilist il) {
   ilist r = malloc(sizeof(struct ilist_ADT));
   r->first = in;
   r->rest = il;   
   return r;
}


// returns an ilist with a in added as the first element of the ilist
// references cease to be valid ilists
// does not promise not to mutate its arguments
ilist icons_destroy(int in, ilist il) {  
     if(iempty_huh(il)) {
             ilist newlist = malloc(sizeof(struct ilist_ADT));
             newlist->rest = iempty();
             newlist->length = 1;
             newlist->first = in;
             return newlist;
     }
    ilist newlist2 = malloc(sizeof(struct ilist_ADT));
    newlist2->length = il->length;
    newlist2->first = il->first;
    newlist2->rest = il->rest;
    il->length = ilength(il) + 1;
    il->rest = newlist2;
    il->first = in;
    return il;
}


// modifies il to remove the first element,
// and returns the modified ilist
// frees memory associated with the first element
ilist irest_destroy(ilist il){ 
   ilist temp = il->rest;
   if(iempty_huh(il) == 1) {
		free(il); return temp;
   }
   il->first = temp->first; 
   il->length = temp->length;  
   il->rest = temp->rest;
   free(temp);
   return il;
}


// returns a new copy of the ilist that continues to be a vild
// ilist with the same elemnts even when il is destroyed
ilist icopy(ilist il){
   if (il== NULL) return NULL;
   int length_temp = il->length;
   
   ilist head = malloc(sizeof(struct ilist_ADT ));
   head ->first = il ->first;
   head ->rest = NULL;
   ilist lstend = head; 
   
   for (ilist a = il ->rest; a != NULL; a = a->rest) {
      ilist tmp = malloc(sizeof(struct ilist_ADT ));
      tmp ->first = a->first;
      tmp ->rest = NULL;
      lstend ->rest = tmp;
      lstend = tmp;
   }
   
   head->length = length_temp;
   return head;
}


// returns the length of an ilist
int ilength(ilist il){
   if (il == NULL) {
      return 0;
   }
   else {
      return il->length;
   }
}


// free memory for entire ilist
void idelete(ilist il){
   while (il != NULL) { 
      ilist next = il->rest;
      free(il);
      il = next;
   }
}