using System;
using System.Collections.Generic;
using System.Linq;

namespace GameAnalyticsSDK.Net.Threading
{
	internal class PriorityQueue<TPriority, TItem>
	{
		readonly SortedDictionary<TPriority, Queue<TItem>> _subqueues;

		public PriorityQueue(IComparer<TPriority> priorityComparer)
		{
			_subqueues = new SortedDictionary<TPriority, Queue<TItem>>(priorityComparer);
		}

		public PriorityQueue() : this(Comparer<TPriority>.Default) { }

		public void Enqueue(TPriority priority, TItem item)
		{
			if (!_subqueues.ContainsKey(priority))
			{
				AddQueueOfPriority(priority);
			}

			_subqueues[priority].Enqueue(item);
		}

		private void AddQueueOfPriority(TPriority priority)
		{
			_subqueues.Add(priority, new Queue<TItem>());
		}

		public TItem Peek()
		{
			if (HasItems)
				return _subqueues.First().Value.Peek();
			else
				throw new InvalidOperationException("The queue is empty");
		}

		public bool HasItems
		{
			get { return _subqueues.Any(); }
		}

		public TItem Dequeue()
		{
			if (_subqueues.Any())
				return DequeueFromHighPriorityQueue();
			else
				throw new InvalidOperationException("The queue is empty");
		}

		private TItem DequeueFromHighPriorityQueue()
		{
			KeyValuePair<TPriority, Queue<TItem>> first = _subqueues.First();
			TItem nextItem = first.Value.Dequeue();
			if (!first.Value.Any())
			{
				_subqueues.Remove(first.Key);
			}
			return nextItem;
		}

		public int Count
		{
			get { return _subqueues.Sum(q => q.Value.Count); }
		}
	}
}