// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.CompilerServices;

namespace System.Collections.ObjectModel
{
    /// <summary>
    /// Read-only wrapper around an ObservableCollection.
    /// </summary>
    [Serializable]
    [DebuggerTypeProxy(typeof(CollectionDebugView<>))]
    [DebuggerDisplay("Count = {Count}")]
    [TypeForwardedFrom("WindowsBase, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
    public class ReadOnlyObservableCollection<T> : ReadOnlyCollection<T>, INotifyCollectionChanged, INotifyPropertyChanged
    {
        /// <summary>
        /// Initializes a new instance of ReadOnlyObservableCollection that
        /// wraps the given ObservableCollection.
        /// </summary>
        public ReadOnlyObservableCollection(ObservableCollection<T> list) : base(list)
        {
            ((INotifyCollectionChanged)Items).CollectionChanged += new NotifyCollectionChangedEventHandler(HandleCollectionChanged);
            ((INotifyPropertyChanged)Items).PropertyChanged += new PropertyChangedEventHandler(HandlePropertyChanged);
        }

        /// <summary>Gets an empty <see cref="ReadOnlyObservableCollection{T}"/>.</summary>
        /// <value>An empty <see cref="ReadOnlyObservableCollection{T}"/>.</value>
        /// <remarks>The returned instance is immutable and will always be empty.</remarks>
        public static new ReadOnlyObservableCollection<T> Empty { get; } = new ReadOnlyObservableCollection<T>(new ObservableCollection<T>());

        /// <summary>
        /// CollectionChanged event (per <see cref="INotifyCollectionChanged" />).
        /// </summary>
        event NotifyCollectionChangedEventHandler? INotifyCollectionChanged.CollectionChanged
        {
            add => CollectionChanged += value;
            remove => CollectionChanged -= value;
        }

        /// <summary>
        /// Occurs when the collection changes, either by adding or removing an item.
        /// </summary>
        /// <remarks>
        /// see <seealso cref="INotifyCollectionChanged"/>
        /// </remarks>
        [field: NonSerialized]
        protected virtual event NotifyCollectionChangedEventHandler? CollectionChanged;

        /// <summary>
        /// raise CollectionChanged event to any listeners
        /// </summary>
        protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
        {
            CollectionChanged?.Invoke(this, args);
        }

        /// <summary>
        /// PropertyChanged event (per <see cref="INotifyPropertyChanged" />).
        /// </summary>
        event PropertyChangedEventHandler? INotifyPropertyChanged.PropertyChanged
        {
            add => PropertyChanged += value;
            remove => PropertyChanged -= value;
        }

        /// <summary>
        /// Occurs when a property changes.
        /// </summary>
        /// <remarks>
        /// see <seealso cref="INotifyPropertyChanged"/>
        /// </remarks>
        [field: NonSerialized]
        protected virtual event PropertyChangedEventHandler? PropertyChanged;

        /// <summary>
        /// raise PropertyChanged event to any listeners
        /// </summary>
        protected virtual void OnPropertyChanged(PropertyChangedEventArgs args)
        {
            PropertyChanged?.Invoke(this, args);
        }

        private void HandleCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
        {
            OnCollectionChanged(e);
        }

        private void HandlePropertyChanged(object? sender, PropertyChangedEventArgs e)
        {
            OnPropertyChanged(e);
        }
    }
}