using System;
using NUnit.Framework;

namespace Developpez.Dotnet.Tests
{
    [TestFixture]
    public class WeakEventTests
    {
        [Test]
        public void Test_AddHandlerAndRaise()
        {
            bool eventRaised = false;

            // Register a handler for Foo on a new object
            var bar = new Bar(() => eventRaised = true);
            Foo += bar.OnFoo;

            // Raise the event
            OnFoo();

            Assert.IsTrue(eventRaised);
        }

        [Test]
        public void Test_RemoveHandler()
        {
            bool eventRaised = false;

            // Register a handler for Foo on a new object
            var bar = new Bar(() => eventRaised = true);
            Foo += bar.OnFoo;

            // Raise the event
            OnFoo();

            Assert.IsTrue(eventRaised);

            // Unregister the handler
            Foo -= bar.OnFoo;

            // Raise the event again
            eventRaised = false;
            OnFoo();

            Assert.IsFalse(eventRaised);
        }

        [Test]
        public void Test_DontPreventGarbageCollection()
        {
            bool eventRaised = false;
            
            // Register a handler for Foo on a new object
            var bar = new Bar(() => eventRaised = true);
            Foo += bar.OnFoo;
            
            // Raise the event
            OnFoo();

            // We still have a reference to bar, so it hasn't been
            // collected and the handler should be called.
            Assert.IsTrue(eventRaised);

            // Drop the reference to bar and force a GC cycle
            bar = null;
            GC.Collect();

            // Raise the event again
            eventRaised = false;
            OnFoo();

            // We don't have a reference to bar anymore, so it should have
            // been collected, and the handler shouldn't be called.
            Assert.IsFalse(eventRaised);
        }

        #region Dummy event and handler class

        private WeakEvent<EventHandler> _fooEvent = new WeakEvent<EventHandler>();
        public event EventHandler Foo
        {
            add { _fooEvent.AddHandler(value); }
            remove { _fooEvent.RemoveHandler(value); }
        }

        protected virtual void OnFoo()
        {
            _fooEvent.Raise(this, EventArgs.Empty);
        }

        class Bar
        {
            private Action _action;
            public Bar(Action action)
            {
                _action = action;
            }

            public void OnFoo(object sender, EventArgs e)
            {
                _action();
            }
        }

        #endregion
    }
}