/* Code by Kowsik Nandagopan D. CSE S3 */
/* Use txt file to input IN to insert, DEL to pop element, DIS to display whole queue*/
/* Header file declaration */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Funtion Declaration */
void inv_stk();
void insert(int);
void inv_stk_A();
void display();

/* Node structure to implement the STACK data structure */
struct Node{
    int data;
    struct Node* next;
};

/* Two Global STACK data structures A and B */
struct Node* STACK_A_TOP = NULL;
struct Node* STACK_B_TOP = NULL;

/* Invert funtion to invert the STACK A to STACK B to get the last elemennt in the STACK A */
void inv_stk(){
    struct Node* temp_A = STACK_A_TOP;
    STACK_B_TOP = NULL;
    struct Node* temp_B = STACK_B_TOP;
    while (temp_A != NULL){
        struct Node* node = (struct Node*) malloc(sizeof(struct Node));
        node->data = temp_A->data;

        if (STACK_B_TOP == NULL){
            node->next = NULL;
            STACK_B_TOP = node;
        } else {
            node->next = STACK_B_TOP;
            STACK_B_TOP = node;
        }
        temp_A = temp_A->next;
    }
}


/* Inset operation on the STACK A to push the newely added elements to the QUEUE. Inserting to the TOP of STACK A */
void insert(int x){
    struct Node* temp = (struct Node*) malloc(sizeof(struct Node));
    temp->data = x;
    if (STACK_A_TOP == NULL){
        temp->next = NULL;
        STACK_A_TOP = temp;
    } else {
        temp->next = STACK_A_TOP;
        STACK_A_TOP = temp;
    }
    inv_stk();
}


/* Inverting back the STACK B back to STACK A as the first element in the STACK B is deleted that is the last element of STACK A */
void inv_stk_A(){
    struct Node* temp = STACK_B_TOP;

    while (temp != NULL){
        insert(temp->data);
        temp = temp->next;
    }
}


/* To display the QUEUE that is the STACK B after inverting the STACK A */
void display(){
    STACK_A_TOP = NULL;
    struct Node* temp = STACK_B_TOP;
    while (temp != NULL){
        printf("%d ", temp->data);
        temp = temp->next;
    }
}

void pop_element(){
    int x;
    if (STACK_B_TOP == NULL) printf("Queue is empty");
    else {
        x = STACK_B_TOP->data;
        struct Node* temp;
        temp = STACK_B_TOP;
        STACK_B_TOP = STACK_B_TOP->next;
        free(temp);
        // Invert the stack B back to A
        inv_stk_A();
        printf("%d", x);
    }
}


void main(int argc, char* argv[]){
    char c[1000];
    int i=0, d;
    /* Reading input form a text file based on the command line argument */
    FILE* f= fopen(argv[1], "r");
    if (!f) printf("NO file named %s", argv[1]);
    else {
        while (fscanf(f, "%s %d\n", c, &d) >= 1)
            /* Insert operation */
            if (strcmp(c, "IN") == 0){
                // printf("IN %d", d);
                insert(d);
                // printf("\n");
            /*Pop Operation*/
            } else if (strcmp(c, "DEL") == 0){
                // printf("POP");
                pop_element();
                printf("\n");
            /* Display whole QUEUE*/
            } else if (strcmp(c, "DIS") == 0){
                // printf("DIS\n");
                display();
                printf("\n");
            }
    }
}