// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT License.
// See the LICENSE file in the project root for more information. 

using System.Collections.Generic;

namespace System.Reactive
{
    /// <summary>
    /// Represents a .NET event invocation consisting of the weakly typed object that raised the event and the data that was generated by the event.
    /// </summary>
    /// <typeparam name="TEventArgs">The type of the event data generated by the event.</typeparam>
    public class EventPattern<TEventArgs> : EventPattern<object, TEventArgs>
    {
        /// <summary>
        /// Creates a new data representation instance of a .NET event invocation with the given sender and event data.
        /// </summary>
        /// <param name="sender">The sender object that raised the event.</param>
        /// <param name="e">The event data that was generated by the event.</param>
#pragma warning disable CA2109 // (Consider making non-public.) This has long been part of the public API so we couldn't change this even if we wanted to.
        public EventPattern(object? sender, TEventArgs e)
#pragma warning restore CA2109
            : base(sender, e)
        {
        }
    }

    /// <summary>
    /// Represents a .NET event invocation consisting of the strongly typed object that raised the event and the data that was generated by the event.
    /// </summary>
    /// <typeparam name="TSender">The type of the sender that raised the event.</typeparam>
    /// <typeparam name="TEventArgs">The type of the event data generated by the event.</typeparam>
    public class EventPattern<TSender, TEventArgs> : IEquatable<EventPattern<TSender, TEventArgs>>, IEventPattern<TSender, TEventArgs>
    {
        /// <summary>
        /// Creates a new data representation instance of a .NET event invocation with the given sender and event data.
        /// </summary>
        /// <param name="sender">The sender object that raised the event.</param>
        /// <param name="e">The event data that was generated by the event.</param>
        public EventPattern(TSender? sender, TEventArgs e)
        {
            Sender = sender;
            EventArgs = e;
        }

        /// <summary>
        /// Gets the sender object that raised the event.
        /// </summary>
        public TSender? Sender { get; }

        /// <summary>
        /// Gets the event data that was generated by the event.
        /// </summary>
        public TEventArgs EventArgs { get; }

        /// <summary>
        /// Deconstructs the event pattern value into a sender and event data.
        /// </summary>
        /// <param name="sender">The sender object that raised the event.</param>
        /// <param name="e">The event data that was generated by the event.</param>
        public void Deconstruct(out TSender? sender, out TEventArgs e) => (sender, e) = (Sender, EventArgs);

        /// <summary>
        /// Determines whether the current <see cref="EventPattern{TSender, TEventArgs}"/> object represents the same event as a specified <see cref="EventPattern{TSender, TEventArgs}"/> object.
        /// </summary>
        /// <param name="other">An object to compare to the current <see cref="EventPattern{TSender, TEventArgs}"/> object.</param>
        /// <returns><c>true</c> if both <see cref="EventPattern{TSender, TEventArgs}"/> objects represent the same event; otherwise, <c>false</c>.</returns>
        public bool Equals(EventPattern<TSender, TEventArgs>? other)
        {
            if (other is null)
            {
                return false;
            }

            if (ReferenceEquals(this, other))
            {
                return true;
            }

            return EqualityComparer<TSender?>.Default.Equals(Sender, other.Sender) && EqualityComparer<TEventArgs>.Default.Equals(EventArgs, other.EventArgs);
        }

        /// <summary>
        /// Determines whether the specified System.Object is equal to the current <see cref="EventPattern{TSender, TEventArgs}"/>.
        /// </summary>
        /// <param name="obj">The System.Object to compare with the current <see cref="EventPattern{TSender, TEventArgs}"/>.</param>
        /// <returns><c>true</c> if the specified System.Object is equal to the current <see cref="EventPattern{TSender, TEventArgs}"/>; otherwise, <c>false</c>.</returns>
        public override bool Equals(object? obj) => Equals(obj as EventPattern<TSender, TEventArgs>);

        /// <summary>
        /// Returns the hash code for the current <see cref="EventPattern{TSender, TEventArgs}"/> instance.
        /// </summary>
        /// <returns>A hash code for the current <see cref="EventPattern{TSender, TEventArgs}"/> instance.</returns>
        public override int GetHashCode()
        {
            var x = Sender?.GetHashCode() ?? 0;
            var y = EventArgs?.GetHashCode() ?? 0;
            return (x << 5) + (x ^ y);
        }

        /// <summary>
        /// Determines whether two specified <see cref="EventPattern{TSender, TEventArgs}"/> objects represent the same event.
        /// </summary>
        /// <param name="first">The first <see cref="EventPattern{TSender, TEventArgs}"/> to compare, or <c>null</c>.</param>
        /// <param name="second">The second <see cref="EventPattern{TSender, TEventArgs}"/> to compare, or <c>null</c>.</param>
        /// <returns><c>true</c> if both <see cref="EventPattern{TSender, TEventArgs}"/> objects represent the same event; otherwise, <c>false</c>.</returns>
        public static bool operator ==(EventPattern<TSender, TEventArgs> first, EventPattern<TSender, TEventArgs> second) => Equals(first, second);

        /// <summary>
        /// Determines whether two specified <see cref="EventPattern{TSender, TEventArgs}"/> objects represent a different event.
        /// </summary>
        /// <param name="first">The first <see cref="EventPattern{TSender, TEventArgs}"/> to compare, or <c>null</c>.</param>
        /// <param name="second">The second <see cref="EventPattern{TSender, TEventArgs}"/> to compare, or <c>null</c>.</param>
        /// <returns><c>true</c> if both <see cref="EventPattern{TSender, TEventArgs}"/> objects don't represent the same event; otherwise, <c>false</c>.</returns>
        public static bool operator !=(EventPattern<TSender, TEventArgs> first, EventPattern<TSender, TEventArgs> second) => !Equals(first, second);
    }
}
