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

  struct product {
     unsigned long long id;
     char name[51];
     double price;
     int quantity;
     int day;
     int month;
     int year;
  };

  struct products {
      struct product val;
      struct products *next;
  };
  int comparedate(int day1, int month1, int year1, int day2, int month2, int year2);
  struct products* find_by_id(struct products*, unsigned long long id);
  int isUniqueID(struct products *products, unsigned long long id);
  void delete_by_id(struct products*, unsigned long long id);
  int change_quantity_of_product(struct products*);
  int print_all_expired_products(struct products*);
  int print_product_with_id(struct products*);
  int add_new_product(struct products*);
  int load_products(struct products*);
  int save_products(struct products*);
  int showproducts(struct products*);
  void free_list(struct products*);

  int main()
   {
    int option = 0,exit_flag = 1;
    struct products *products = NULL;
    //products = malloc(sizeof(struct products));
  // if (products == NULL)
    //{
    //   printf("Memory allocation error");
    //  return 1;
   // }
   // products->next;
    if (load_products(products) == 1)
    {
      printf("Memory allocation error");
      return 1;
    }

       while(exit_flag)
    {
        system("@cls||clear");
    printf(" *****************/MENU\\*****************\n");
    printf("*                                        *\n");
    printf("*   1.Add new item in the warehouse      *\n");
    printf("*   2.Change the quantity                *\n");
    printf("*   3.Display the expired items          *\n");
    printf("*   4.Display information for item       *\n");
    printf("*   5.Show products in the warehouse     *\n");
    printf("*   6.Exit                               *\n");
    printf("*                                        *\n");
    printf("******************************************\n");
        printf("Insert option: ");
        if (scanf("%d", &option) == EOF)
        {
            break;
        }
         fflush(stdin);
        switch (option) {
            case 1:
                if (add_new_product(products)) {
                    return -1;
                }
                break;
            case 2:
                if (change_quantity_of_product(products)) {
                    return -1;
                }
                break;
            case 3:
                if (print_all_expired_products(products)) {
                    return -1;
                }
                break;
            case 4:
                if (print_product_with_id(products)) {
                    return -1;
                }
                break;
              case 5:
                if (showproducts(products)) {
                    return ;
                }
                break;
            case 6:
                exit_flag = 0;
                break;
            default:
                break;
        }
        fflush(stdin);

      system("pause");
    }

   if (save_products(products))
    {
        return 1;
    }
    free_list(products);
    return 0;
 }
    void free_list(struct products *products)
    {
        struct products *curr_item=products;
        while(products!=NULL)
        {
            products=products->next;
            free(curr_item);
            curr_item=products;
        }
    }

    int comparedate(int day1, int month1, int year1, int day2, int month2, int year2)
{
    if(year2>year1)
    {
        return 1;
    }
    else if(year2==year1 && month2>month1)
    {
        return 1;
    }
    else if(year2==year1 && month2==month1 && day2>=day1)
    {
        return 1;
    }
    return 0;
}
int print_all_expired_products(struct products *products)
  {
     if(products==NULL)
    {
        printf("List is empty!\n");
        return;
    }
    struct products* current_product;

    int day,month,year;
    printf("Enter date(DD/MM/YYYY): ");
    scanf("%d/%d/%d",&day,&month,&year);
    //struct products *iterate_products = products->next;
    for(current_product=products;current_product!=NULL;current_product=current_product->next)
    {
        if(comparedate(current_product->val.day,current_product->val.month,current_product->val.year,day,month,year))
        {
            printf("id: %llu\n", current_product->val.id);
            printf("name: %s\n", current_product->val.name);
            printf("price: %.2f\n",current_product->val.price);
            printf("quantity: %d\n", current_product->val.quantity);
            //printf("date: %s\n", iterate_products->val.date);
        }
    }
        //iterate_products = iterate_products->next;

    return 0;
  }
   int isUniqueID(struct products *products, unsigned long long id)
  {
    while(products)
    {
        if(products->val.id == id)
        {
            printf("ID already exist!\n");
            return 0;
        }
    products = products->next;
        }
  return 1;
 }

   int load_products(struct products *products)
   {
      FILE *fp;
      if ((fp = fopen("data", "rb")) == NULL)
        {
          printf("The file cannot be opened");
          exit(1);
        }

      struct products *prev_products = products;
      struct products *curr_products = NULL;
      while (1)
      {
          struct product product;
          if (fread(&product, sizeof(struct product), 1, fp) != 1)
           {
              if (feof(fp))
              {
                  break;
              }
             printf("reading error");
             break;
           }

        curr_products = malloc(sizeof(struct products));
        if (curr_products == NULL)
        {
            printf("Memory allocation error");
            return 1;
        }
        curr_products->val = product;
        curr_products->next = NULL;

        prev_products->next = curr_products;
        prev_products = curr_products;
    }
      fclose(fp);
      return 0;
  }
int showproducts(struct products* products)
{
    if(products==NULL)
    {
        printf("List is empty!\n");
        return 1;
    }
    struct products* current_product;
    for(current_product=products;current_product!=NULL;current_product=current_product->next)
    {
            printf("id: %llu\n", current_product->val.id);
            printf("name: %s\n", current_product->val.name);
            printf("price: %.2f\n", current_product->val.price);
            printf("quantity: %d\n", current_product->val.quantity);
            printf("date: %d.%d.%d\n", current_product->val.day,current_product->val.month,current_product->val.year);
    }
    return 0;
}
    int save_products(struct products *products)
    {
      FILE *fp  = NULL;
      if ((fp = fopen("data", "ab")) == NULL)
      {
        printf("The file cannot be opened");
       return 2;
      }
       while (1)
      {
         products = products->next;
         if (products == NULL)
         {
            break;
         }

        if (fwrite(&products->val, sizeof(struct product), 1, fp) != 1)
        {
            printf("writening error");
            break;
        }
     }
     fclose(fp);
     return 0;
    }

    struct products* find_by_id(struct products *products,unsigned long long id)
  {
    struct products *iterate_products = products->next;
    while(1)
    {
        if (iterate_products == NULL)
        {
            printf("The warehouse is empty.");
            exit(212);
        }
        if (iterate_products->val.id == id)
        {
            return iterate_products;
        }
       iterate_products = iterate_products->next;
    }
    return NULL;
  }

   void delete_by_id(struct products *products, unsigned long long id)
  {
      struct products *prev_products = products;
      struct products *iterate_products = products->next;
      while(1)
      {
        if (iterate_products == NULL)
        {
            printf("The warehouse is empty.");
            break;
        }
        if (iterate_products->val.id == id)
        {
            prev_products->next = iterate_products->next;
            break;
        }
        iterate_products = iterate_products->next;
        prev_products = prev_products->next;
      }
  }



int add_new_product(struct products *products)
{
   struct product product;
   unsigned long long id=0;
   do{
        printf("Insert id: ");
        fflush(stdin);
        scanf("%llu", &product.id);
    }while(!(isUniqueID(products, product.id)) || product.id > 999999999999|| product.id<100000000000);

    printf("Insert name: ");
    scanf("%50s",product.name);
    printf("Insert price: ");
    scanf("%lf", &product.price);
    printf("Insert quantity: ");
    scanf("%d", &product.quantity);;
    printf("Insert date /in dd.mm.yyyy format/: ");
    scanf("%d/%d/%d",&product.day,&product.month,&product.year);
    if(product.month<1 || product.month>12 || product.day<1 || product.day>31 || product.year<0)
    {
        printf("The date is incorrect.");
        return 1;
    }

    struct products *last_products = products;
    while(last_products->next)
    {
        last_products = last_products->next;
    }

    struct products *next_products = NULL;
    next_products = malloc(sizeof(struct products));
    if (next_products==NULL)
    {
        printf("Memory allocation error.");
        return 1;
    }
    next_products->val = product;
    next_products->next = NULL;
    last_products->next = next_products;
    return 0;
}

int print_product_with_id(struct products *products)
 {
    unsigned long long id=0;
    printf("Insert id: ");
    scanf("%llu", &id);

    struct products *products_with_id = find_by_id(products, id);
    if (products_with_id == NULL)
        printf("Missing product!\n");
    else
    {
        printf("id: %llu\n", products_with_id->val.id);
        printf("name: %s\n", products_with_id->val.name);
        printf("price: %.2f\n", products_with_id->val.price);
        printf("quantity: %d\n", products_with_id->val.quantity);
        printf("date: %.2d/%.2d/%.4d;\n", products_with_id->val.day,products_with_id->val.month,products_with_id->val.year);
    }
    return 0;
   }

   int change_quantity_of_product(struct products *products)
{
    unsigned long long id=0;int quantity=0;
    printf("Insert id: ");
    scanf(" %llu", &id);
    printf("Insert quantity to change[(+)for adding and (-)for subtraction]:");
    scanf("%d", &quantity);
    struct products *products_with_id = find_by_id(products, id);
    if (products_with_id == NULL)
    printf("Missing product!\n");
    else
    {
       int new_quantity = products_with_id->val.quantity + quantity;
       if (new_quantity < 0)
             printf("Quantity to change is bigger than product quantity!\n");
       else if (new_quantity > 0)
               products_with_id->val.quantity = new_quantity;
       else if (new_quantity == 0)
               delete_by_id(products, id);
    }
 return 0;
}