// EventQueue.cpp : definition of the EventQueue class functions

#include <cstdlib>
#include <cassert>

#include "EventQueue.h"
#include "Aircraft.h"
#include "Event.h"

EventQueue::EventQueue () {
	length = 0;
	front = NULL;
	rear = NULL;
}


// = true if the queue is empty
bool EventQueue::isEmpty () const {
	return (length == 0);
}


// Inserts the event pointed to by 'e' into the queue
// *** at present enqueue is implemented using just 'front'.You ***
// *** have to implement enqueue using both 'front' and 'rear'  ***
// *** In other words, you should not traverse the entire queue ***
// *** like a linked list to insert an event at the end of the  ***
// *** linked list. Instead YOU SHOULD KEEP A REAR POINTER AND  ***
// *** USE THAT                                                 ***                                        
void EventQueue::enqueue (Event *e) {
	assert (e != NULL);

	QueueNode *temp, *newNode;
	temp = front;

	newNode = new QueueNode;// create the new node that will be added to the queue
	newNode->e = e;
	newNode->next = NULL;

	// if the queue is empty
	if (temp == NULL) {
		front = newNode;
		length = 1;			// queue was intially empty, so new length is 1
		return;
	}

	// if the queue is not empty, the go till the end of the queue to insert the element
	while (temp->next != NULL) {
		temp = temp->next;
	}
	temp->next = newNode;
	length = length + 1;	// update the length of the queue
	return;

}


// The usual dequeue function for a queue. It returns NULL if the queue is empty
// *** implement this using 'front' and 'rear' ***
Event* EventQueue::dequeue () {
	if (isEmpty ())
		return NULL;		// return NULL if the queue is empty

	QueueNode *temp = front;
	front = front->next;	// remove the first element of the queue		
	length = length - 1;	// update the length of the queue

	Event *event = temp->e;
	delete temp;			// release the memory used up by the node just dequeued
	temp = NULL;

	return event;

}


// = returns the length of the queue
int EventQueue::getLength () const {
	return length;
}


// = returns the i-th (counted from front) event from the queue
// If i is less than one or greater than the length, it returns NULL
Event* EventQueue::getIthEvent (int i) {
	if (i < 1 || i > length)
		return NULL;

	int count = 1;
	QueueNode *temp = front;
	while (count < i) {
		temp = temp->next;
		count++;
	}

	return temp->e;
}


// the destructor, which invokes a helper function, deleteQueue 
EventQueue::~EventQueue () {
	deleteQueue (front);
}


// a helper function used by the destructor. It deletes all the nodes in the queue
void EventQueue::deleteQueue (QueueNode *n) {
    if (n != NULL) {
		deleteQueue (n->next);
		delete n->e;	// delete the event contained in the node
		delete n;		// delete the node itself
	}
}