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

void printMenu();
char* getStr();
char* changeFamilyName(char* husbandFullName, char* wifeFullName, int option);
void strcpyByIndex(char* destination, char* source, int start, int size);

void main() {
    printf("Enter the husband's full name: ");
    char* husbandFullName = getStr();
    if (!husbandFullName)
        return;

    printf("Enter the wife's full name: ");
    char* wifeFullName = getStr();
    if (!wifeFullName)
        return;

    printMenu();
    int option;
    printf("Enter your decision: ");
    scanf("%d", &option);

    char* newName = changeFamilyName(husbandFullName, wifeFullName, option);
    if (!newName)
        return;

    printf("\nBefore the visit:\n%s\n%s\n\n", husbandFullName, wifeFullName);

    switch (option) {
    case 1:
        free(husbandFullName);
        husbandFullName = newName;
        break;
    case 2:
        free(husbandFullName);
        husbandFullName = newName;
        break;
    case 3:
        free(wifeFullName);
        wifeFullName = newName;
        break;
    case 4:
        free(wifeFullName);
        wifeFullName = newName;
        break;
    }

    printf("After the visit:\n%s\n%s\n\n", husbandFullName, wifeFullName);

    // allocated "newName" is also freed by using these
    free(husbandFullName);
    free(wifeFullName);
}

void printMenu() {
    printf("Please select one of the folowing options [1-5]: \n");
    printf("1 - Change first partner's last name to second partner's last name.\n");
    printf("2 - Add second partner's last name to first partner's full name.\n");
    printf("3 - Change second partner's last name to first partner's last name.\n");
    printf("4 - Add first partner's last name to second partner's full name.\n");
    printf("5 – Decide Later.\n\n");
}

char* getStr() {
    char* str[51];
    gets_s(str, 50);

    char* allocatedStr = (char*)malloc((strlen(str) + 1) * sizeof(char));
    if (!allocatedStr) {
        printf("error. couldn't allocate the requsted memory.");
        return NULL;
    }

    strcpy(allocatedStr, str);

    return allocatedStr;
}

char* changeFamilyName(char* husbandFullName, char* wifeFullName, int option) {
    if (!(option <= 5 && option >= 1)) {
        printf("error: option must be 1-5");
        return NULL;
    }

    if (!*husbandFullName || !*wifeFullName) { // string are known to be initialized, checking if the first char isn't null
        printf("error: empty string.");
        return NULL;
    }

    char* husbandFirstName;
    char* husbandLastName;
    char* wifeFirstName;
    char* wifeLastName;

    int husbandFirstNameSize;
    int husbandLastNameSize;
    int wifeFirstNameSize;
    int wifeLastNameSize;

    int i;
    for (i = 0; *(husbandFullName + i) != ' '; i++); // husband's first name
    husbandFirstNameSize = i;
    i++;
    husbandFirstName = (char*)malloc(i * sizeof(char));

    for (i = 0; *(husbandFullName + i); i++); // husband's last name
    husbandLastNameSize = i;
    husbandLastName = (char*)malloc((i + 1) * sizeof(char));

    for (i = 0; *(wifeFullName + i) != ' '; i++); // wife's first name
    wifeFirstNameSize = i;
    i++;
    wifeFirstName = (char*)malloc(i * sizeof(char));

    for (i = 0; *(wifeFullName + i); i++); // wife's last name
    wifeLastNameSize = i;
    wifeLastName = (char*)malloc((i + 1) * sizeof(char));

    if (!husbandFirstName || !husbandLastName || !wifeFirstName || !wifeLastName) {
        printf("error: couldnt allocate the requested memory.");
        return NULL;
    }

    strcpyByIndex(husbandFirstName, husbandFullName, 0, husbandFirstNameSize);
    strcpyByIndex(husbandLastName, husbandFullName, husbandFirstNameSize + 1, husbandLastNameSize);
    strcpyByIndex(wifeFirstName, wifeFullName, 0, wifeFirstNameSize);
    strcpyByIndex(wifeLastName, wifeFullName, wifeFirstNameSize + 1, wifeLastNameSize);

    char* newFullName = NULL;

    switch (option) {
    case 1:
        newFullName = (char*)malloc((husbandFirstNameSize + wifeLastNameSize + 2) * sizeof(char));
        if (!newFullName) {
            printf("error: couldnt allocate the requested memory.");
            return NULL;
        }

        strcpy(newFullName, husbandFirstName);
        strcat(newFullName, " ");
        strcat(newFullName, wifeLastName);
        break;
    case 2:
        newFullName = (char*)malloc((strlen(husbandFullName) + wifeLastNameSize + 2) * sizeof(char));
        if (!newFullName) {
            printf("error: couldnt allocate the requested memory.");
            return NULL;
        }

        strcpy(newFullName, husbandFullName);
        strcat(newFullName, " ");
        strcat(newFullName, wifeLastName);
        break;
    case 3:
        newFullName = (char*)malloc((wifeFirstNameSize + husbandLastNameSize + 2) * sizeof(char));
        if (!newFullName) {
            printf("error: couldnt allocate the requested memory.");
            return NULL;
        }

        strcpy(newFullName, wifeFirstName);
        strcat(newFullName, " ");
        strcat(newFullName, husbandLastName);
        break;
    case 4:
        newFullName = (char*)malloc((strlen(wifeFullName) + husbandLastNameSize + 2) * sizeof(char));
        if (!newFullName) {
            printf("error: couldnt allocate the requested memory.");
            return NULL;
        }

        strcpy(newFullName, wifeFullName);
        strcat(newFullName, " ");
        strcat(newFullName, husbandLastName);
        break;
    case 5:
        printf("\ndecide later chosen\n");
        break;
    default:
        printf("error: option must be between 1 and 5");
        return NULL;
    }

    free(husbandFirstName);
    free(husbandLastName);
    free(wifeFirstName);
    free(wifeLastName);

    return newFullName;
}


void strcpyByIndex(char* destination, char* source, int start, int size) {
    int i;
    for (i = start; i < size + start; i++) {
        *(destination + i - start) = *(source + i);
    }
    *(destination + i - start) = 0;
}