/* 
* Code example for CP264 Data Structures II
* circular array queue, modified from textbook example
* HBF 
*/
#include <stdio.h>

#define MAX 10
void enqueue(int queue[], int *front, int *rear, int val);
int dequeue(int queue[], int *front, int *rear);
int peek(int queue[], int front, int rear);
int display(int queue[], int front, int rear);

int main() {
  int queue[MAX];
  int front = -1, rear = -1;
  
  int i, n=10, val;
  printf("\nEnqueue:\n");
  for (i=0; i<n; i++) {
    enqueue(queue, &front, &rear, i);
  }
  
  printf("\nDisplay all:\n");
  display(queue, front, rear);
  
  val = peek(queue, front, rear);
  printf("\nPeek value: %d", val);

  val = dequeue(queue, &front, &rear);
  printf("\nDequeue value: %d", val);

  val = dequeue(queue, &front, &rear);
  printf("\nDequeue value: %d", val);
  
  printf("\nEnqueue value: %d\n", 20);
  enqueue(queue, &front, &rear, 20);
  printf("\nEnqueue value: %d\n", 30);
  enqueue(queue, &front, &rear, 30);
  printf("\nDisplay all:\n");
  display(queue, front, rear);
  return 0;
}

void enqueue(int queue[], int *front, int *rear, int val) {
  if ((*front == 0 && *rear == MAX - 1) || (*rear == *front -1)  )
    printf("\n OVERFLOW");
  else if (*front == -1 && *rear == -1) {
    *front = 0;
    *rear = 0;
    queue[*rear] = val;
    
  } else if (*rear == MAX - 1 && *front != 0) {
    *rear = 0;
    queue[*rear] = val;
  } else {
    *rear = *rear + 1;
    queue[*rear] = val;
  }
}

int dequeue(int queue[], int *front, int *rear) {
  int val = -1;
  if ((*front == -1 && *rear == -1) || *front == *rear) {
    printf("\n UNDERFLOW");
    return -1;
  }
  val = queue[*front];
  if (*front == *rear) {
    *front = -1;
    *rear = -1;
  } else {
    if (*front == MAX - 1)
      *front = 0;
    else
      *front = *front + 1;
  }
  return val;
}

int peek(int queue[], int front, int rear) {
  if ((front == -1 && rear == -1) || front == rear) {
    printf("\n QUEUE IS EMPTY");
    return -1;
  } else {
    return queue[front];
  }
}

int display(int queue[], int front, int rear) {
  int i;
  if (front == -1 && rear ==-1 )
    printf("\nQUEUE IS EMPTY");
  else {
    if (front < rear) {
      for (i = front; i <= rear; i++)
        printf("%d ", queue[i]);
    } else {
      for (i = front; i < MAX; i++)
        printf("%d ", queue[i]);
      for (i = 0; i <= rear; i++)
        printf("%d ", queue[i]);
    }
  }
}

/*
Enqueue:

Display all:
0 1 2 3 4 5 6 7 8 9
Peek value: 0
Dequeue value: 0
Dequeue value: 1
Enqueue value: 20

Enqueue value: 30

Display all:
2 3 4 5 6 7 8 9 20 30 
*/