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

typedef struct list_node list_node;
typedef list_node *linked_list;

struct list_node {
    int       data;
    list_node *next;
};

/*
 * return 1 iff list contains no elements, 0 otherwise
 */
int
empty(linked_list list) {
    return list == NULL;
}

/*
 * create a list_node and place the specified values in the fields
 */
linked_list
create_node(int data, linked_list next) {
    list_node *n;

    n = malloc(sizeof (list_node));
    if (n == NULL) {
        fprintf(stderr, "out of memory\n");
        exit(1);
    }
    n->data = data;
    n->next = next;
    return n;
}

/*
 * insert integer at front of list
 */
linked_list
insert(int value, linked_list list) {
    return create_node(value, list);
}

/*
 * return pointer to last node in list
 * NULL is returned if list is empty
 */
list_node *
last(linked_list list) {
    list_node *n = list;
    if (n == NULL)
        return NULL;
    while (n->next != NULL)
        n = n->next;
    return n;
}


/*
 * append integer to end of list
 */
linked_list
append(int value, linked_list list) {
    list_node *n;

    n =  create_node(value, NULL); /* will be last node in list */

    if (empty(list)) {
       return n;                  /* new node is now  head of the list */
    } else {
        last(list)->next = n;  /* append node to list */
        return list;
    }
}


/*
 * find previous node to first node containing specified int
 */
list_node *
find_previous(int i, linked_list list) {
    list_node *previous = NULL;
    list_node *x;
    
    for (x = list; x != NULL; x = x->next) {
        if (x->data == i)
            return previous;
        previous = x;
    }
    
    return NULL;
}

/*
 * delete first node containing specified int
 */
linked_list
delete(int i, linked_list list) {
    list_node *deleted = NULL;
    list_node *previous = find_previous(i, list);
    
    if (previous != NULL) {
    	deleted = previous->next;
        previous->next = previous->next->next;
    } else if (list != NULL && list->data == i) {
    	deleted = list;
        list = list->next;
    }
    if (deleted != NULL)
    	free(deleted);
    return list;
}

/*
 * print contents of list in Haskell syntax
 */
void
print_list(linked_list list) {
    list_node *n;
    
    printf("[");
    for (n = list; n != NULL; n = n->next) {
        printf("%d", n->data);
        if (n->next != NULL)
            printf(", ");
    }
    printf("]");
}

/*
 * return number of nodes in list
 */
int
length(linked_list list) {
	/* your code goes here */
	return 0;
}

/*
 * return nth node in list, counting from 0
 * 0 is returned and an error message printed
 * if the list doesn't have an nth node
 */
int
nth(int index, linked_list list) {
	/* your code goes here */
   return 0;
}

/*
 * reverse the nodes in list
 */
linked_list
reverse(linked_list list) {
	/* your code goes here */
	return NULL;
}

enum {
    MAX_LINE = 1024
};
/*
 * test the above functions
 */
int
main(int argc, char *argv[]) {
    linked_list list;
    int argument;
    char *s, *t;
    char line[MAX_LINE];
    char action[MAX_LINE];
    
    list = NULL;
    while (1) {
        printf("list = ");
        print_list(list);
        printf("\n");
        printf("> ");
        if (fgets(line, MAX_LINE, stdin) == NULL)
            break;
        
        for (s = line; isspace(*s); s++)
            ;
        
        t = action;
        while (isalpha(*s))
            *t++ = *s++;
        *t = '\0';
        
        argument = strtol(s, &s, 10);

        if (strcmp(action, "quit") == 0)
            break;
        else if (strcmp(action, "") == 0)
            continue;
        else if (strcmp(action, "insert") == 0)
            list = insert(argument, list);
        else if (strcmp(action, "append") == 0)
            list = append(argument, list);
        else if (strcmp(action, "delete") == 0)
            list = delete(argument, list);
        else if (strcmp(action, "length") == 0)
            printf("%d\n", length(list));
        else if (strcmp(action, "nth") == 0)
            printf("%d\n", nth(argument, list));
         else if (strcmp(action, "reverse") == 0)
            list = reverse(list);
       else
            printf("Unknown command: '%s'\n", action);
    }
    return 0;
}