// broken_inventory.c
//
// Written by YOUR-NAME (YOUR-ZID)
// on TODAYS-DATE
//
// Manages a simple game inventory as a linked list of items.
// The game keeps crashing! Find and fix the bugs below.

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

#define MAX_NAME_LENGTH 20

struct item {
    char name[MAX_NAME_LENGTH];
    int quantity;
    struct item *next;
};

struct item *create_item(char *name, int quantity);
struct item *append_item(struct item *inventory, char *name, int quantity);
struct item *use_item(struct item *inventory, char *name);
void print_inventory(struct item *inventory);
void free_inventory(struct item *inventory);

// -----------------------------------------------------------------------------
//////////////// DO NOT CHANGE THE MAIN FUNCTION ///////////////////////////
int main(void) {
    struct item *inventory = NULL;

    inventory = append_item(inventory, "Potion", 3);
    inventory = append_item(inventory, "Sword", 1);

    printf("== Starting inventory ==\n");
    print_inventory(inventory);

    printf("\nUsing the Potion.\n");
    inventory = use_item(inventory, "Potion");
    print_inventory(inventory);

    printf("\nUsing the Sword.\n");
    inventory = use_item(inventory, "Sword");
    print_inventory(inventory);

    free_inventory(inventory);
    return 0;
}

// ---------------------------------------------------------------------------
// BUGGY FUNCTIONS - FIX THESE
// ---------------------------------------------------------------------------

// Creates a new item and returns a pointer to it. 
struct item *create_item(char *name, int quantity) {
    struct item new_item;
    strcpy(new_item.name, name);
    new_item.quantity = quantity;
    new_item.next = NULL;
    return &new_item;
}

// Adds a new item to the inventory and returns the updated head of
// the inventory list.
struct item *append_item(struct item *inventory, char *name, int quantity) {
    struct item *new_item = create_item(name, quantity);

    struct item *current = inventory;
    while (current->next != NULL) {
        current = current->next;
    }
    current->next = new_item;

    return inventory;
}

// Decreases the quantity of the item with the given name by 1.
// If the quantity reaches 0, the item is removed from the inventory.
struct item *use_item(struct item *inventory, char *name) {
    struct item *current = inventory;
    struct item *prev = NULL;

    while (current != NULL && strcmp(current->name, name) != 0) {
        prev = current;
        current = current->next;
    }

    current->quantity--;
    if (current->quantity <= 0) {
        free(current);
        if (prev == NULL) {
            inventory = current->next;
        } else {
            prev->next = current->next;
        }
    }
    
    return inventory;
}

// Free all items in the inventory.
void free_inventory(struct item *inventory) {
    free(inventory);
}

// ---------------------------------------------------------------------------
// PROVIDED FUNCTIONS - DO NOT CHANGE THESE
// ---------------------------------------------------------------------------

void print_inventory(struct item *inventory) {
    printf("====== Inventory ======\n");
    struct item *current = inventory;
    if (current == NULL) {
        printf("    (empty)\n");
        return;
    }
    while (current != NULL) {
        printf("    %s x%d\n", current->name, current->quantity);
        current = current->next;
    }
}