using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Threading;

namespace InABox.Core
{
    public class ObservableDictionary<TKey, TValue> :
        ICollection<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>,
        INotifyCollectionChanged, INotifyPropertyChanged
    {
        private readonly SynchronizationContext _context;
        private readonly ConcurrentDictionary<TKey, TValue> _dictionary;

        /// <summary>
        ///     Initializes an instance of the ObservableConcurrentDictionary class.
        /// </summary>
        public ObservableDictionary()
        {
            _context = AsyncOperationManager.SynchronizationContext;
            _dictionary = new ConcurrentDictionary<TKey, TValue>();
        }

        /// <summary>Event raised when the collection changes.</summary>
        public event NotifyCollectionChangedEventHandler CollectionChanged;

        /// <summary>Event raised when a property on the collection changes.</summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        ///     Notifies observers of CollectionChanged or PropertyChanged of an update to the dictionary.
        /// </summary>
        private void NotifyObserversOfChange()
        {
            var collectionHandler = CollectionChanged;
            var propertyHandler = PropertyChanged;
            if (collectionHandler != null || propertyHandler != null)
                _context.Post(s =>
                {
                    if (collectionHandler != null) collectionHandler(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
                    if (propertyHandler != null)
                    {
                        propertyHandler(this, new PropertyChangedEventArgs("Count"));
                        propertyHandler(this, new PropertyChangedEventArgs("Keys"));
                        propertyHandler(this, new PropertyChangedEventArgs("Values"));
                    }
                }, null);
        }

        /// <summary>Attempts to add an item to the dictionary, notifying observers of any changes.</summary>
        /// <param name="item">The item to be added.</param>
        /// <returns>Whether the add was successful.</returns>
        private bool TryAddWithNotification(KeyValuePair<TKey, TValue> item)
        {
            return TryAddWithNotification(item.Key, item.Value);
        }

        /// <summary>Attempts to add an item to the dictionary, notifying observers of any changes.</summary>
        /// <param name="key">The key of the item to be added.</param>
        /// <param name="value">The value of the item to be added.</param>
        /// <returns>Whether the add was successful.</returns>
        private bool TryAddWithNotification(TKey key, TValue value)
        {
            var result = _dictionary.TryAdd(key, value);
            if (result) NotifyObserversOfChange();
            return result;
        }

        /// <summary>Attempts to remove an item from the dictionary, notifying observers of any changes.</summary>
        /// <param name="key">The key of the item to be removed.</param>
        /// <param name="value">The value of the item removed.</param>
        /// <returns>Whether the removal was successful.</returns>
        private bool TryRemoveWithNotification(TKey key, out TValue value)
        {
            var result = _dictionary.TryRemove(key, out value);
            if (result) NotifyObserversOfChange();
            return result;
        }

        /// <summary>Attempts to add or update an item in the dictionary, notifying observers of any changes.</summary>
        /// <param name="key">The key of the item to be updated.</param>
        /// <param name="value">The new value to set for the item.</param>
        /// <returns>Whether the update was successful.</returns>
        private void UpdateWithNotification(TKey key, TValue value)
        {
            _dictionary[key] = value;
            NotifyObserversOfChange();
        }

        #region ICollection<KeyValuePair<TKey,TValue>> Members

        void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
        {
            TryAddWithNotification(item);
        }

        void ICollection<KeyValuePair<TKey, TValue>>.Clear()
        {
            ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Clear();
            NotifyObserversOfChange();
        }

        bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item)
        {
            return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Contains(item);
        }

        void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
        {
            ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).CopyTo(array, arrayIndex);
        }

        int ICollection<KeyValuePair<TKey, TValue>>.Count => ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Count;

        bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly => ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).IsReadOnly;

        bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
        {
            TValue temp;
            return TryRemoveWithNotification(item.Key, out temp);
        }

        #endregion

        #region IEnumerable<KeyValuePair<TKey,TValue>> Members

        IEnumerator<KeyValuePair<TKey, TValue>> IEnumerable<KeyValuePair<TKey, TValue>>.GetEnumerator()
        {
            return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).GetEnumerator();
        }

        #endregion

        #region IDictionary<TKey,TValue> Members

        public void Add(TKey key, TValue value)
        {
            TryAddWithNotification(key, value);
        }

        public bool ContainsKey(TKey key)
        {
            return _dictionary.ContainsKey(key);
        }

        public ICollection<TKey> Keys => _dictionary.Keys;

        public bool Remove(TKey key)
        {
            TValue temp;
            return TryRemoveWithNotification(key, out temp);
        }

        public bool TryGetValue(TKey key, out TValue value)
        {
            return _dictionary.TryGetValue(key, out value);
        }

        public ICollection<TValue> Values => _dictionary.Values;

        public TValue this[TKey key]
        {
            get => _dictionary[key];
            set => UpdateWithNotification(key, value);
        }

        #endregion
    }
}