package com.limelight.nvstream.av;

import java.util.Iterator;
import java.util.LinkedList;

import com.limelight.LimeLog;

public class RtpReorderQueue {
	private final int maxSize;
	private final int maxQueueTime;
	private final LinkedList<RtpQueueEntry> queue;
	
	private short nextRtpSequenceNumber;
	
	private long oldestQueuedTime;
	private RtpQueueEntry oldestQueuedEntry;
	
	public enum RtpQueueStatus {
		HANDLE_IMMEDIATELY,
		QUEUED_NOTHING_READY,
		QUEUED_PACKETS_READY,
		REJECTED
	};
	
	public RtpReorderQueue() {
		this.maxSize = 16;
		this.maxQueueTime = 40;
		this.queue = new LinkedList<RtpQueueEntry>();
		
		this.oldestQueuedTime = Long.MAX_VALUE;
		this.nextRtpSequenceNumber = Short.MAX_VALUE;
	}
	
	public RtpReorderQueue(int maxSize, int maxQueueTime) {
		this.maxSize = maxSize;
		this.maxQueueTime = maxQueueTime;
		this.queue = new LinkedList<RtpQueueEntry>();
		
		this.oldestQueuedTime = Long.MAX_VALUE;
		this.nextRtpSequenceNumber = Short.MAX_VALUE;
	}
	
	private boolean queuePacket(boolean head, RtpPacketFields packet) {
		short seq = packet.getRtpSequenceNumber();
		
		if (nextRtpSequenceNumber != Short.MAX_VALUE) {
			// Don't queue packets we're already ahead of
			if (SequenceHelper.isBeforeSigned(seq, nextRtpSequenceNumber, false)) {
				return false;
			}
			
			// Don't queue duplicates either
			for (RtpQueueEntry existingEntry : queue) {
				if (existingEntry.sequenceNumber == seq) {
					return false;
				}
			}
		}
		
		RtpQueueEntry entry = new RtpQueueEntry();
		entry.packet = packet;
		entry.queueTime = System.currentTimeMillis();
		entry.sequenceNumber = seq;
		
		if (oldestQueuedTime == Long.MAX_VALUE) {
			oldestQueuedTime = entry.queueTime;
			oldestQueuedEntry = entry;
		}
		
		if (head) {
			queue.addFirst(entry);
		}
		else {
			queue.addLast(entry);
		}
		
		return true;
	}
	
	private void updateOldestQueued() {
		oldestQueuedTime = Long.MAX_VALUE;
		oldestQueuedEntry = null;
		for (RtpQueueEntry entry : queue) {
			if (entry.queueTime < oldestQueuedTime) {
				oldestQueuedEntry = entry;
				oldestQueuedTime = entry.queueTime;
			}
		}
	}
	
	private RtpQueueEntry getEntryByLowestSeq() {
		if (queue.isEmpty()) {
			return null;
		}
		
		RtpQueueEntry lowestSeqEntry = queue.getFirst();
		short nextSeq = lowestSeqEntry.sequenceNumber;
		
		for (RtpQueueEntry entry : queue) {
			if (SequenceHelper.isBeforeSigned(entry.sequenceNumber, nextSeq, true)) {
				lowestSeqEntry = entry;
				nextSeq = entry.sequenceNumber;
			}
		}
		
		if (nextSeq != Short.MAX_VALUE) {
			nextRtpSequenceNumber = nextSeq;
		}
		
		return lowestSeqEntry;
	}
	
	private RtpQueueEntry validateQueueConstraints() {
		if (queue.isEmpty()) {
			return null;
		}
		
		boolean needsUpdate = false;
		
		// Check that the queue's time constraint is satisfied
		if (System.currentTimeMillis() - oldestQueuedTime > maxQueueTime) {
			LimeLog.info("Discarding RTP packet queued for too long");
			queue.remove(oldestQueuedEntry);
			needsUpdate = true;
		}
		
		// Check that the queue's size constraint is satisfied
		if (queue.size() == maxSize) {
			LimeLog.info("Discarding RTP packet after queue overgrowth");
			queue.remove(oldestQueuedEntry);
			needsUpdate = true;
		}
		
		if (needsUpdate) {
			// Recalculate the oldest entry if needed
			updateOldestQueued();
			
			// Return the lowest seq queued
			return getEntryByLowestSeq();
		}
		else {
			return null;
		}
	}
	
	public RtpQueueStatus addPacket(RtpPacketFields packet) {
		if (nextRtpSequenceNumber != Short.MAX_VALUE &&
			SequenceHelper.isBeforeSigned(packet.getRtpSequenceNumber(), nextRtpSequenceNumber, false)) {
			// Reject packets behind our current sequence number
			return RtpQueueStatus.REJECTED;
		}
		
		if (queue.isEmpty()) {
			// Return immediately for an exact match with an empty queue
			if (nextRtpSequenceNumber == Short.MAX_VALUE ||
				packet.getRtpSequenceNumber() == nextRtpSequenceNumber) {
				nextRtpSequenceNumber = (short) (packet.getRtpSequenceNumber() + 1);
				return RtpQueueStatus.HANDLE_IMMEDIATELY;
			}
			else {				
				// Queue is empty currently so we'll put this packet on there
				if (queuePacket(false, packet)) {
					return RtpQueueStatus.QUEUED_NOTHING_READY;
				}
				else {
					return RtpQueueStatus.REJECTED;
				}
			}
		}
		else {
			// Validate that the queue remains within our contraints
			RtpQueueEntry lowestEntry = validateQueueConstraints();
			
			// If the queue is now empty after validating queue constraints,
			// this packet can be returned immediately
			if (lowestEntry == null && queue.isEmpty()) {
				nextRtpSequenceNumber = (short) (packet.getRtpSequenceNumber() + 1);
				return RtpQueueStatus.HANDLE_IMMEDIATELY;
			}
			
			// Queue has data inside, so we need to see where this packet fits
			if (packet.getRtpSequenceNumber() == nextRtpSequenceNumber) {
				// It fits in a hole where we need a packet, now we have some ready
				if (queuePacket(true, packet)) {
					return RtpQueueStatus.QUEUED_PACKETS_READY;
				}
				else {
					return RtpQueueStatus.REJECTED;
				}
			}
			else {
				if (queuePacket(false, packet)) {
					// Constraint validation may have changed the oldest packet to one that
					// matches the next sequence number 
					return (lowestEntry != null) ? RtpQueueStatus.QUEUED_PACKETS_READY :
						RtpQueueStatus.QUEUED_NOTHING_READY;
				}
				else {
					return RtpQueueStatus.REJECTED;
				}
			}
		}
	}
	
	public RtpPacketFields getQueuedPacket() {
		RtpQueueEntry queuedEntry = null;
		
		// Find the matching entry
		Iterator<RtpQueueEntry> i = queue.iterator();
		while (i.hasNext()) {
			RtpQueueEntry entry = i.next();
			if (entry.sequenceNumber == nextRtpSequenceNumber) {
				nextRtpSequenceNumber++;
				queuedEntry = entry;
				i.remove();
				break;
			}
		}
		
		// Bail if we found nothing
		if (queuedEntry == null) {
			// Update the oldest queued packet time
			updateOldestQueued();
			
			return null;
		}
		
		// We don't update the oldest queued entry here, because we know
		// the caller will call again until it receives null
		
		return queuedEntry.packet;
	}
	
	private class RtpQueueEntry {
		public RtpPacketFields packet;
		
		public short sequenceNumber;
		public long queueTime;
	}
}