/*
 * Author  : Amit Dutta <amitdutta4255@gmail.com>
 * Date    : 08 Feb 2026
 * Repo    : https://github.com/notamitgamer/bsc
 * License : MIT License (See the LICENSE file for details)
 */

/* Update Master file (Roll, Name) using Transaction file (Roll, Code Add/Delete). Both files are sorted by Roll.
*/
/* Let Us C, Chap- 19 (File Input/Output), Qn No.: B(i) */

/* This file is auto-generated by a bot. */
/* This code is not compiled; it is for reference only. */


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

struct student {
    int roll;
    char name[30];
};

struct trans {
    int roll;
    char code; // 'A' for Add, 'D' for Delete
    char name[30]; // Only needed for Add
};

void create_files();

int main()
{
    FILE *fm, *ft, *fn;
    struct student m;
    struct trans t;
    int has_m, has_t;

    create_files();

    fm = fopen("MASTER.DAT", "rb");
    ft = fopen("TRANS_ROLL.DAT", "rb");
    fn = fopen("NEW_MASTER.DAT", "wb");

    if (!fm || !ft || !fn) exit(1);

    has_m = fread(&m, sizeof(struct student), 1, fm);
    has_t = fread(&t, sizeof(struct trans), 1, ft);

    printf("Merging Master and Transaction files...\n");

    while (has_m && has_t)
    {
        if (m.roll < t.roll)
        {
            // No transaction for this master record, keep it
            fwrite(&m, sizeof(struct student), 1, fn);
            has_m = fread(&m, sizeof(struct student), 1, fm);
        }
        else if (m.roll == t.roll)
        {
            // Transaction affects this record
            if (t.code == 'D')
            {
                printf("Deleting Roll %d\n", m.roll);
                // Skip writing 'm' to file (Deleting)
                has_m = fread(&m, sizeof(struct student), 1, fm);
            }
            else
            {
                // Logic error: Can't ADD if ID exists. Maybe Update?
                // Assuming replace or skip. Let's skip T and keep M for now.
                has_m = fread(&m, sizeof(struct student), 1, fm);
            }
            has_t = fread(&t, sizeof(struct trans), 1, ft);
        }
        else // m.roll > t.roll
        {
            // Transaction ID is new
            if (t.code == 'A')
            {
                struct student new_s;
                new_s.roll = t.roll;
                strcpy(new_s.name, t.name);
                fwrite(&new_s, sizeof(struct student), 1, fn);
                printf("Adding Roll %d\n", new_s.roll);
            }
            has_t = fread(&t, sizeof(struct trans), 1, ft);
        }
    }

    // Process remaining Master
    while (has_m)
    {
        fwrite(&m, sizeof(struct student), 1, fn);
        has_m = fread(&m, sizeof(struct student), 1, fm);
    }

    // Process remaining Transactions (Only Adds)
    while (has_t)
    {
        if (t.code == 'A')
        {
            struct student new_s = {t.roll, ""};
            strcpy(new_s.name, t.name);
            fwrite(&new_s, sizeof(struct student), 1, fn);
            printf("Adding Roll %d\n", new_s.roll);
        }
        has_t = fread(&t, sizeof(struct trans), 1, ft);
    }

    fclose(fm); fclose(ft); fclose(fn);
    return 0;
}

void create_files()
{
    struct student m[] = {{10, "A"}, {20, "B"}, {30, "C"}};
    struct trans t[] = {{15, 'A', "NewGuy"}, {20, 'D', ""}, {40, 'A', "LastGuy"}};
    
    FILE *f1 = fopen("MASTER.DAT", "wb");
    fwrite(m, sizeof(struct student), 3, f1);
    fclose(f1);

    FILE *f2 = fopen("TRANS_ROLL.DAT", "wb");
    fwrite(t, sizeof(struct trans), 3, f2);
    fclose(f2);
}