using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;

namespace System.Application.Serialization
{
	[DebuggerDisplay("Value={Value}, Key={Key}, Default={Default}")]
	public abstract class SerializablePropertyBase<T> : INotifyPropertyChanged
	{
		private T _value;
		private bool _cached;

		public string Key { get; }

		public ISerializationProvider Provider { get; }

		public bool AutoSave { get; set; }

		public T Default { get; }

		public virtual T Value
		{
			get
			{
				if (this._cached) return this._value;

				if (!this.Provider.IsLoaded)
				{
					this.Provider.Load();
				}

				object obj;
				if (this.Provider.TryGetValue(this.Key, out obj))
				{
					this._value = this.DeserializeCore(obj);
					this._cached = true;
				}
				else
				{
					this._value = this.Default;
				}

				return this._cached ? this._value : this.Default;
			}
			set
			{
				if (this._cached && Equals(this._value, value)) return;

				if (!this.Provider.IsLoaded)
				{
					this.Provider.Load();
				}

				var old = this._value;
				this._value = value;
				this._cached = true;
				this.Provider.SetValue(this.Key, this.SerializeCore(value));
				this.OnValueChanged(old, value);

				if (this.AutoSave) this.Provider.Save();
			}
		}

		protected SerializablePropertyBase(string key, ISerializationProvider provider) : this(key, provider, default(T)) { }

		protected SerializablePropertyBase(string key, ISerializationProvider provider, T defaultValue)
		{
			if (key == null) throw new ArgumentNullException(nameof(key));
			if (provider == null) throw new ArgumentNullException(nameof(provider));

			this.Key = key;
			this.Provider = provider;
			this.Default = defaultValue;

			this.Provider.Reloaded += (sender, args) =>
			{
				if (this._cached)
				{
					this._cached = false;

					var oldValue = this._value;
					var newValue = this.Value;
					if (!Equals(oldValue, newValue))
					{
						this.OnValueChanged(oldValue, newValue);
					}
				}
				else
				{
					var oldValue = default(T);
					var newValue = this.Value;
					this.OnValueChanged(oldValue, newValue);
				}
			};
		}


		protected virtual object SerializeCore(T value)
		{
			return value;
		}

		protected virtual T DeserializeCore(object value)
		{
			return (T)value;
		}


		public virtual IDisposable Subscribe(Action<T> listener)
		{
			listener(this.Value);
			return new ValueChangedEventListener(this, listener);
		}

		public virtual void Reset()
		{
			if (!this.Provider.IsLoaded)
			{
				this.Provider.Load();
			}

			object old;
			if (this.Provider.TryGetValue(this.Key, out old))
			{
				if (this.Provider.RemoveValue(this.Key))
				{
					this._value = default(T);
					this._cached = false;
					this.OnValueChanged(this.DeserializeCore(old), this.Default);

					if (this.AutoSave) this.Provider.Save();
				}
			}
		}

		private class ValueChangedEventListener : IDisposable
		{
			private readonly Action<T> _listener;
			private readonly SerializablePropertyBase<T> _source;

			public ValueChangedEventListener(SerializablePropertyBase<T> property, Action<T> listener)
			{
				this._listener = listener;
				this._source = property;
				this._source.ValueChanged += this.HandleValueChanged;
			}

			private void HandleValueChanged(object sender, ValueChangedEventArgs<T> args)
			{
				this._listener(args.NewValue);
			}

			public void Dispose()
			{
				this._source.ValueChanged -= this.HandleValueChanged;
			}
		}


		public static implicit operator T(SerializablePropertyBase<T> property)
		{
			return property.Value;
		}


		#region events

		public event EventHandler<ValueChangedEventArgs<T>> ValueChanged;

		protected virtual void OnValueChanged(T oldValue, T newValue)
		{
			this.ValueChanged?.Invoke(this, new ValueChangedEventArgs<T>(oldValue, newValue));
		}

		private readonly Dictionary<PropertyChangedEventHandler, EventHandler<ValueChangedEventArgs<T>>> _handlers
			= new Dictionary<PropertyChangedEventHandler, EventHandler<ValueChangedEventArgs<T>>>();

		event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
		{
			add { this.ValueChanged += (this._handlers[value] = (sender, args) => value(sender, new PropertyChangedEventArgs(nameof(this.Value)))); }
			remove
			{
				EventHandler<ValueChangedEventArgs<T>> handler;
				if (this._handlers.TryGetValue(value, out handler))
				{
					this.ValueChanged -= handler;
					this._handlers.Remove(value);
				}
			}
		}

		#endregion
	}
}