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

namespace ln.collections
{
	public class Cache<TKey, TValue>
	{
		public TimeSpan DefaultLifeTime { get; set; }
		private readonly Dictionary<TKey, Entry> _cache = new Dictionary<TKey, Entry>();

		public Cache(TimeSpan defaultLifeTime)
		{
			DefaultLifeTime = defaultLifeTime;
		}

		public Cache()
			: this(TimeSpan.FromMinutes(10))
		{
		}

		public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
		{
			lock (this)
			{
				foreach (var cacheEntry in _cache)
				{
					if (cacheEntry.Value.IsValid)
						array[arrayIndex++] = new KeyValuePair<TKey, TValue>(cacheEntry.Key, cacheEntry.Value.Value);
				}
			}
		}

		public int Count {
			get
			{
				lock (this) { return _cache.Count; }
			}
		}

		public bool IsReadOnly => false;
		public void Clear() { lock (this) _cache.Clear(); }
		public void Cleanup()
		{
			lock (this)
			{
				foreach (var key in _cache.Keys.ToArray())
				{
					if (!_cache[key].IsValid)
						_cache.Remove(key);
				}
			}
		}

		public bool Contains(KeyValuePair<TKey, TValue> item) { lock (this) return TryGetValue(item.Key, out TValue value) && object.Equals(item.Value, value); }
		public void Add(KeyValuePair<TKey, TValue> item) => Add(item.Key, item.Value);

		public bool Remove(KeyValuePair<TKey, TValue> item)
		{
			lock (this)
			{
				if (_cache.TryGetValue(item.Key, out Entry entry) && object.Equals(item.Value, entry.Value))
				{
					_cache.Remove(item.Key);
					return entry.IsValid;
				}

				return false;
			}
		}


		public void Add(TKey key, TValue value)
		{
			lock (this)
			{
				_cache.Add(key, new Entry(this, value));
			}
		}

		public bool ContainsKey(TKey key)
		{
			lock (this) return _cache.ContainsKey(key) && _cache[key].IsValid;
		}
		public bool Remove(TKey key)
		{
			lock (this) return _cache.Remove(key);
		}

		public bool TryGetValue(TKey key, out TValue value)
		{
			lock (this)
			{
				if (_cache.TryGetValue(key, out Entry entry))
				{
					if (entry.IsValid)
					{
						value = entry.Value;
						return true;
					}
					else
					{
						_cache.Remove(key);
					}
				}
			}
			
			value = default(TValue);
			return false;
		}

		public TValue this[TKey key]
		{
			get
			{
				lock (this)
				{
					if (TryGetValue(key, out TValue value))
						return value;
				}

				throw new KeyNotFoundException();
			}
			set
			{
				lock (this)
				{
					if (_cache.TryGetValue(key, out Entry entry))
						entry.Reset(value);
					else
						_cache.Add(key, new Entry(this, value));
				}
			}
		}

		public bool ReValidate(TKey key)
		{
			lock (this)
			{
				if (_cache.TryGetValue(key, out Entry entry))
				{
					if (entry.IsValid)
					{
						entry.UpdateTimestamp();
						return true;
					}
					else
					{
						_cache.Remove(key);
					}
				}

				return false;
			}
		}

		public TValue GetOrCreate(TKey key, Func<TKey, TValue> factory)
		{
			lock (this)
			{
				if (!TryGetValue(key, out TValue value))
				{
					value = factory(key);
					Add(key, value);
				}
				return value;
			}
		}
		
		class Entry
		{
			private Cache<TKey, TValue> _cache;
			public DateTime TimeOut { get; private set; }
			public TValue Value { get; private set; }

			public Entry(Cache<TKey,TValue> cache, TValue value)
			{
				_cache = cache;
				Value = value;
				UpdateTimestamp();
			}

			public void UpdateTimestamp() => UpdateTimestamp(_cache.DefaultLifeTime);
			public void UpdateTimestamp(TimeSpan lifeTime) => TimeOut = DateTime.Now + lifeTime;
			public bool IsValid => TimeOut > DateTime.Now;

			public void Reset(TValue newValue)
			{
				Value = newValue;
				UpdateTimestamp();
			}
		}
		
	}

	public abstract class KeyedCache<TKey, TValue> : Cache<TKey, TValue>
	{
		protected KeyedCache()
		{
		}
		protected KeyedCache(TimeSpan defaultTimeOut)
		:base(defaultTimeOut)
		{
		}
		
		protected abstract TKey GetKey(TValue value);

		public void Add(TValue value) => Add(GetKey(value), value);
		public bool RemoveValue(TValue value)
		{
			TKey key = GetKey(value);
			lock (this)
			{
				if (TryGetValue(key, out TValue cachedValue) && object.Equals(cachedValue, value))
				{
					return Remove(key);
				}
			}

			return false;
		}

	}
}