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

#define STRING_SIZE 250

/* data types */
typedef struct list_node_struct {
   char node_string[STRING_SIZE]; /* string held in this node */
   struct list_node_struct *next; /* pointer to next node */
} list_node;

typedef list_node *string_list;

/* function headers */
string_list create_list();
int add_string(string_list *l, char *s);
void print_list(string_list l);
int search_string(string_list l, char *s);
int delete_string(string_list *l, char *s);
void clean_list(string_list *l);
void encrypt_string(char *s, int k);
void encrypt_list(string_list l, int k);

/* main command parser */
int main() {

  char buffer[2*STRING_SIZE], command[2*STRING_SIZE], string[2*STRING_SIZE];
  char *word;
  string_list sl = create_list();
  int offset;

  while(1) {
    printf("Enter a command: ");
    fgets(buffer,sizeof(buffer),stdin);
    word = strtok(buffer," \t\n");
    strcpy(command, word);
    word = strtok(NULL,"\n");
    if( word != NULL )
      strcpy(string, word);

    if (strcmp(command,"end") == 0) {

      clean_list(&sl);
      printf("Thanks, it's been fun.\n");
      return 0;

    } else if (strcmp(command,"print") == 0) {

      print_list(sl);

    } else if (strcmp(command,"add") == 0) {

      if (add_string(&sl,string))
	printf("Add successful!\n\n");
      else
	printf("Add unsuccessful.\n\n");

    } else if (strcmp(command,"delete") == 0) {

      if (delete_string(&sl,string))
	printf("Delete successful!\n\n");
      else
	printf("Delete unsuccessful.\n\n");

    } else if (strcmp(command,"search") == 0) {

      printf("The string '%s' is ", string);
      if (!search_string(sl,string)) printf("not ");
      printf("in the list.\n\n");

    } else if (strcmp(command,"encrypt") == 0) {

      offset = atoi(string);
      if (offset <= 0) {
	printf("Encryption unsuccessful.\n\n"); 
      } else {
	encrypt_list(sl,offset);
	printf("Encryption successful!\n\n");
      }

    } else if (strcmp(command,"clean") == 0) {

      clean_list(&sl);
      printf("List has been cleaned.\n\n");

    } else {

      printf("Couldn't understand your command.\n\n");

    }
  } 
}


/* Your functions should go here */