// Source: https://github.com/PrismLibrary/Prism/blob/7f0b1680bbe754da790274f80851265f808d9bbf

#region Copyright .NET Foundation, Licensed under the MIT License (MIT)
// The MIT License (MIT)
//
// Copyright(c).NET Foundation
//
// All rights reserved. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following conditions: 
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#endregion

#if !FEATURE_CONDITIONALWEAKTABLE_ENUMERATOR

using System;
using System.Collections.Generic;
using System.Threading;

namespace Lucene.Net.Util.Events
{
    /// <summary>
    /// Implements <see cref="IEventAggregator"/>.
    /// </summary>
    internal class EventAggregator : IEventAggregator
    {
        private readonly Dictionary<Type, EventBase> events = new Dictionary<Type, EventBase>();
        // Captures the sync context for the UI thread when constructed on the UI thread 
        // in a platform agnostic way so it can be used for UI thread dispatching
        private readonly SynchronizationContext syncContext = SynchronizationContext.Current;

        /// <summary>
        /// Gets the single instance of the event managed by this EventAggregator. Multiple calls to this method with the same <typeparamref name="TEventType"/> returns the same event instance.
        /// </summary>
        /// <typeparam name="TEventType">The type of event to get. This must inherit from <see cref="EventBase"/>.</typeparam>
        /// <returns>A singleton instance of an event object of type <typeparamref name="TEventType"/>.</returns>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1004:GenericMethodsShouldProvideTypeParameter")]
        public TEventType GetEvent<TEventType>() where TEventType : EventBase, new()
        {
            lock (events)
            {
                EventBase existingEvent = null;

                if (!events.TryGetValue(typeof(TEventType), out existingEvent))
                {
                    TEventType newEvent = new TEventType();
                    newEvent.SynchronizationContext = syncContext;
                    events[typeof(TEventType)] = newEvent;

                    return newEvent;
                }
                else
                {
                    return (TEventType)existingEvent;
                }
            }
        }
    }
}

#endif
