using Sarand.Net.Standard.Base.App;
using System;
using System.Collections.Generic;
using System.Text;

namespace Sarand.Net.Standard.Base.Core
{
	//=======================================================================
	/// <summary>
	/// Dictionary with items queued as if in FIFO list.
	/// </summary>
	/// <typeparam name="K">Type of key</typeparam>
	/// <typeparam name="V">Type of value</typeparam>
	public class SacsQueueDictionary<K, V>
	{
		//-------------------------------------------------------------------
		// Data memners.
		private readonly Queue<K> queue = new Queue<K>();
		private readonly Dictionary<K, V> dictionary = new Dictionary<K, V>();

		//-------------------------------------------------------------------
		// Properties.
		public int Count { get { lock (dictionary) return queue.Count; } }

		//-------------------------------------------------------------------
		/// <summary>
		/// Is the KLey defined in the queue dictionary.
		/// </summary>
		/// <param name="key"></param>
		/// <returns>True if found, else false.</returns>
		public bool HasValue(K key)
		{
			lock (dictionary)
			{
				return dictionary.ContainsKey(key);
			}
		}

		//-------------------------------------------------------------------
		/// <summary>
		/// Retrieve the value determined by the key.
		/// </summary>
		/// <param name="key"></param>
		/// <returns>Corresponding value if present, else default value.</returns>
		public V GetValue(K key)
		{
			V value = default(V);
			lock (dictionary)
			{
				dictionary.TryGetValue(key, out value);
			}
			return value;
		}

		//-------------------------------------------------------------------
		public bool SetEntry(K key, V value)
		{
			if (key == null || value == null) return false;
			lock (dictionary)
			{
				if (!dictionary.ContainsKey(key))
				{
					// New Key - Add to queue before setting value in dictionary.
					queue.Enqueue(key);
				}
				// Value is set or reset in dictionary whetehr previously exists or not.
				dictionary[key] = value;
			}
			if (SacsSystem.DebugMode) Validate();
			return true;
		}

		//-------------------------------------------------------------------
		/// <summary>
		/// Remove the top n entries from the queue dictionary.
		/// </summary>
		/// <param name="maxEntries"></param>
		/// <returns></returns>
		public List<KeyValuePair<K, V>> RemoveTopEntries(int maxEntries)
		{
			List<KeyValuePair<K, V>> entries = new List<KeyValuePair<K, V>>();
			lock (dictionary)
			{
				while (queue.Count > 0 && entries.Count < maxEntries)
				{
					K key = queue.Dequeue();
					V value = dictionary[key];
					entries.Add(new KeyValuePair<K, V>(key, value));
					dictionary.Remove(key);
				}
			}
			if (SacsSystem.DebugMode) Validate();
			return entries;
		}

		//-------------------------------------------------------------------
		// Internal utilities.
		//-------------------------------------------------------------------
		private void Validate()
		{
			lock (dictionary)
			{
				if (queue.Count != dictionary.Count)
					throw new NotSupportedException("SacsQueueDictionary.Validate Inconsistent entry counts. Quete: " + queue.Count + ". Dictionary: " + dictionary.Count);
			}
		}

		//-------------------------------------------------------------------
	}
	//=======================================================================
}