Umbraco-CMS/src/Umbraco.Core/Events/CancellableEventArgs.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace Umbraco.Core.Events
{
    /// <summary>
    /// Represents event data for events that support cancellation.
    /// </summary>
    public class CancellableEventArgs : EventArgs, IEquatable<CancellableEventArgs>
    {
        private bool _cancel;
        private IDictionary<string, object> _eventState;

        private static readonly ReadOnlyDictionary<string, object> EmptyAdditionalData = new ReadOnlyDictionary<string, object>(new Dictionary<string, object>());

        public CancellableEventArgs(bool canCancel, EventMessages messages, IDictionary<string, object> additionalData)
        {
            CanCancel = canCancel;
            Messages = messages;
            AdditionalData = new ReadOnlyDictionary<string, object>(additionalData);
        }

        public CancellableEventArgs(bool canCancel, EventMessages eventMessages)
        {
            if (eventMessages == null) throw new ArgumentNullException("eventMessages");
            CanCancel = canCancel;
            Messages = eventMessages;
            AdditionalData = EmptyAdditionalData;
        }

        public CancellableEventArgs(bool canCancel)
        {
            CanCancel = canCancel;
            //create a standalone messages
            Messages = new EventMessages();
            AdditionalData = EmptyAdditionalData;
        }

        public CancellableEventArgs(EventMessages eventMessages)
            : this(true, eventMessages)
        { }

        public CancellableEventArgs()
            : this(true)
        { }

        /// <summary>
        /// Flag to determine if this instance will support being cancellable
        /// </summary>
        public bool CanCancel { get; set; }

        /// <summary>
        /// If this instance supports cancellation, this gets/sets the cancel value
        /// </summary>
        public bool Cancel
        {
            get
            {
                if (CanCancel == false)
                {
                    throw new InvalidOperationException("This event argument class does not support canceling.");
                }
                return _cancel;
            }
            set
            {
                if (CanCancel == false)
                {
                    throw new InvalidOperationException("This event argument class does not support canceling.");
                }
                _cancel = value;
            }
        }

        /// <summary>
        /// if this instance supports cancellation, this will set Cancel to true with an affiliated cancellation message
        /// </summary>
        /// <param name="cancelationMessage"></param>
        public void CancelOperation(EventMessage cancelationMessage)
        {
            Cancel = true;
            cancelationMessage.IsDefaultEventMessage = true;
            Messages.Add(cancelationMessage);
        }

        /// <summary>
        /// Returns the EventMessages object which is used to add messages to the message collection for this event
        /// </summary>
        public EventMessages Messages { get; }

        /// <summary>
        /// In some cases raised evens might need to contain additional arbitrary readonly data which can be read by event subscribers
        /// </summary>
        /// <remarks>
        /// This allows for a bit of flexibility in our event raising - it's not pretty but we need to maintain backwards compatibility
        /// so we cannot change the strongly typed nature for some events.
        /// </remarks>
        public ReadOnlyDictionary<string, object> AdditionalData { get; set; }

        /// <summary>
        /// This can be used by event subscribers to store state in the event args so they easily deal with custom state data between a starting ("ing")
        /// event and an ending ("ed") event
        /// </summary>
        public IDictionary<string, object> EventState
        {
            get => _eventState ?? (_eventState = new Dictionary<string, object>());
            set => _eventState = value;
        }

        public bool Equals(CancellableEventArgs other)
        {
            if (ReferenceEquals(null, other)) return false;
            if (ReferenceEquals(this, other)) return true;
            return Equals(AdditionalData, other.AdditionalData);
        }

        public override bool Equals(object obj)
        {
            if (ReferenceEquals(null, obj)) return false;
            if (ReferenceEquals(this, obj)) return true;
            if (obj.GetType() != GetType()) return false;
            return Equals((CancellableEventArgs) obj);
        }

        public override int GetHashCode()
        {
            return AdditionalData != null ? AdditionalData.GetHashCode() : 0;
        }

        public static bool operator ==(CancellableEventArgs left, CancellableEventArgs right)
        {
            return Equals(left, right);
        }

        public static bool operator !=(CancellableEventArgs left, CancellableEventArgs right)
        {
            return Equals(left, right) == false;
        }
    }
}