#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <malloc.h>

// structure definition
struct node {
    char name[50];
    int age;
    int student_no;
    char nationality[50];
    struct node *next;
};
typedef struct node *NODE_T;

// function declarations
void enter_new_data();
void remove_existing_data();
void display_all_data();
void remove_existing_data();
void show_options();
NODE_T getnode();
void freenode(NODE_T p);
void free_buffer();
void continue_f(char message[100]);

// global variables
char ch;

// create linked-list's main holder variable
NODE_T students,conductor;

int main(){

    // iniatilize students linked-list by NULL
    students = NULL;

    // show the options that user has
    show_options();

    return 1;
}

// this function will list options that user can apply
void show_options(){

    system("cls"); // clear screen

    int opt,opt_bool=0;

    printf("%s\n\n%s\n%s\n%s\n%s\n\n","The Options You Have","1. Add New Student's Record","2. Delete An Existing Student's Record","3. Display The List Of Students","4. Exit");


    while(opt_bool != 1){
        printf("Operation:  ");
        scanf("%d",&opt);

        if(opt == 1 || opt == 2 || opt == 3 || opt == 4){
            opt_bool = 1;
        }

    }

    // check the operation and go to the operation
    if(opt == 1){ // adding record
        enter_new_data();
    } else if(opt == 2){ // removing record
        remove_existing_data();
    } else if(opt == 3){ // displaying records
        display_all_data();
    } else if(opt == 4){ // exit the program
        exit(0);
    }
}

// enter new student data into linked-list
void enter_new_data(){

    system("cls"); // clear screen

    // get a new node
    NODE_T p = getnode();

    printf("You are entering a new student's record\n");

    // take student's name
    printf("Student's Name: ");
    scanf("%s",p->name);
    free_buffer();

    // take student's age
    printf("Student's Age: ");
    scanf("%d",&p->age);
    free_buffer();

    // take student's number
    printf("Student's Number: ");
    scanf("%d",&p->student_no);
    free_buffer();

    // take student's nationality
    printf("Student's Nationality: ");
    scanf("%s",p->nationality);
    free_buffer();

    // set p->next next value of last node of linked-list, which is equal to 0
    p->next = 0;

    conductor = students; // assign linked-list to the conductor to traverse

    // if there is no any node yet, add node p as first node
    if(conductor == NULL) {
        students = p; // since this will be first node of the linked-list we are assigning it to the students
    } else {

        // reach the last node
        while (conductor->next != 0)
        {
            conductor = conductor->next;
        }

        conductor->next = p; // append the node p to the linked list
    conductor = conductor->next;
    }


    continue_f("Adding new record is done."); // ask press any key to continue

    show_options(); // show options

}

// to display all data of linked list
void display_all_data(){

    system("cls"); // clear screen

    printf("The Student Records\n\n");

    printf("%20s%10s%20s%20s","STUDENT'S NAME","AGE","STUDENT'S NUMBER","NATIONALITY"); // captions

    conductor = students; // assign linked-list to the conductor to traverse

    if (conductor != NULL ) { /* Makes sure there is a place to start */
        // traverse untill last node
        do {

            printf("\n%20s%10d%20d%20s",conductor->name,conductor->age,conductor->student_no,conductor->nationality); // record

            conductor = conductor->next;
        } while (conductor != NULL);
    } else {
        printf("\n\n There is not any record yet."); // print that we don't have ant record yet
    }

    continue_f("Listing records is done."); // ask press any key to continue

    show_options(); // show options
}

// to display all data of linked list
void remove_existing_data(){

    system("cls"); // clear screen

    printf("The Student Deletion\n\n");

    conductor = students; // assign linked-list to the conductor to traverse

    if (conductor != NULL ) { /* Makes sure there is a place to start */

        int std_num;
        NODE_T p,prev = conductor;

        printf("Type student number of student who you want to delete from the list.\nStudent number: ");
        scanf("%d",&std_num); // assign entered number into std_num variable
        free_buffer();

        // check if first node is one we are looking for
        if(conductor->student_no == std_num) {

            students = conductor->next; // assign current node into prev struct pointer in order to reach previous node

        } else {

            // traverse untill last node
            while (conductor != NULL) {

                // if the current node is student we are looking for break the loop
                if(conductor->student_no == std_num){

                    break;
                }

                prev = conductor; // assign current node into prev struct pointer in order to reach previous node

                conductor = conductor->next; // jump to the next node
            }

            // if the std_num match any record
            if(conductor != NULL)
                prev->next = conductor->next; // change the previous node's next pointer to next pointer value of the node that we are goşng to remove

        }

        // if record is found
        if(conductor != NULL) {

            printf("\n1 record is deleted.\n\n");
            printf(" Name: %s\n Age: %d\n Student Numer: %d\n Nationality: %s",conductor->name,conductor->age,conductor->student_no,conductor->nationality); // print the record

            freenode(conductor); // free the node removed from the linked-list
        } else {
            // if there is not record matc with entered student number
            printf("\n Student not found.");
        }
    } else {
        printf(" There is not any record to delete yet."); // print that we don't have ant record yet
    }

    continue_f("Deleting operation is done."); // ask press any key to continue

    show_options(); // show options
}

// create new node
NODE_T getnode(void){
    NODE_T p;
    p = (struct node *) malloc(sizeof(struct node));
    return p;
}

// set free a node
void freenode(NODE_T p){
    free(p);
}

// clear the buffer if there are any extra data in it
void free_buffer(){
    while (getchar() != '\n') { }
}

void continue_f(char message[100]){
    printf("\n\n%s\nPress any key to continue...",message);
    getch(); // wait for pushing any key from user
}