/* Program to read a binary file of restaurant menu items to make a check
   for a customer.

   Input:  Binary file "anx17-02.bin" containing one menu_item structure
           (see below) per line in the input file.
           Terminal entry of menu item numbers until EOF.
           Warning: no check for illegal terminal input.
   Output: A file "prntfile" containing a check showing listed item names,
           descriptions, and prices, and a bill total.

This program illustrates the use of the fseek() function to locate a record
in a file of many identical entries.

*/

typedef struct {
    char name[31];              /* item name */
    char description[51];       /* item description */
    int  price;                 /* price in cents */
} menu_item;

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>              /* for tolower() */
#include "lst10-7.c"            /* for file_open function */

void display_instructions_and_headings(FILE *printfile);
void process_order(FILE *infile, FILE *printfile);

main() {
    FILE *infile, *printfile;

    infile = file_open("anx17-02.bin", "rb");   /* open file for binary input */
    printfile = file_open("prntfile", "w");     /* for printer output */

    display_instructions_and_headings(printfile);

    process_order(infile, printfile);

    fclose(infile);
    fclose(printfile);
    printf("Order complete - see file \"prntfile\"\n");
}

void process_order(FILE *infile, FILE *printfile) {
    menu_item item;
    int status;
    long cost=0;  /* Total order cost: long as order may exceed $327.67 */
    long item_cost; /* cost of one item in cents */
    int item_no, quantity;
    char answer;

    /* Now process a customer order.  Ask the number of the menu items,
       and for each one, look up the entry in the infile.  Item 1 will
       be at the start of this file, so it will have offset zero from the
       start.  That is, each entry is offset by its item number minus 1
       from the start.  To locate an item, this offset must be multiplied
       by the length of each item, that is, the sizeof a menu_item.
       The order will be complete when zero is entered for an item number.
    */

    while (
        printf("Enter an item number and quantity, or EOF when finished: ")
        ,                /*  <<<--- a comma operator */
        status = scanf("%d %d", &item_no, &quantity)
        ,
        status == 2 && item_no > 0
    ) {
        status = fseek(infile, (sizeof item) * (long)(item_no - 1), SEEK_SET);

        /* Status is 0 if fseek succeeded.  Now test that and try to input
           an item from the seek'd position.
        */

        if (status != 0 || fread(&item, sizeof item, 1, infile) != 1) {
            fprintf(stderr, "Cannot locate item in file.\n");
        } else {
            /* Here we have an item - process it. */

            printf("Order for %d %s. Correct (Y/N)? ", quantity, item.name);
            scanf(" %c", &answer);
            answer = tolower(answer);       /* Turn capitals to lower case. */

            if (answer == 'y') {
                printf("Adding item to order.\n");
                item_cost = (long)item.price * quantity;
                cost += item_cost;
                fprintf(
                    printfile, "%3d     %-20.20s %-40.40s %6.2f\n",
                    quantity, item.name, item.description,
                    (float)item_cost / 100   /* cost in dollars */
                );
            } else {
                printf("Item cancelled.\n");
            }
        }
    }

    /* Now finalise the order */
    fprintf(printfile, "\nTotal:%70.2f\n\f", (float)cost / 100);
}

void display_instructions_and_headings(FILE *printfile) {
    /* Outputs instructions to the user and prints the order heading */
    fprintf(
        printfile,
        "\t\tRestaurant Order\n\n"
        "Number\tName\t\t     Description\t\t\t\tCost\n\n"
    );
    printf(
        "Restaurant Menu Selector\n"
        "Enter the number of a menu item and then the quantity.\n"
        "Repeat for all menu items, then enter EOF\n\n"
    );
}