/*
    Copyright (C) 2014-2019 de4dot@gmail.com

    This file is part of dnSpy

    dnSpy is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    dnSpy is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with dnSpy.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.Threading.Tasks;

namespace dnSpy.Contracts.Debugger.DotNet.Evaluation {
	/// <summary>
	/// Invokes code on another thread.
	/// </summary>
	public abstract class DbgDotNetDispatcher {
		/// <summary>
		/// Throws if the current thread isn't the dispatcher thread
		/// </summary>
		public void VerifyAccess() {
			if (!CheckAccess())
				throw new InvalidOperationException("Wrong dispatcher thread");
		}

		/// <summary>
		/// Checks whether the current thread is the dispatcher thread
		/// </summary>
		/// <returns></returns>
		public abstract bool CheckAccess();

		/// <summary>
		/// Executes code asynchronously on the dispatcher thread. This method returns immediately even if
		/// it happens to be called on the dispatcher thread.
		/// </summary>
		/// <param name="callback">Code to execute</param>
		public abstract void BeginInvoke(Action callback);

		/// <summary>
		/// Executes code asynchronously on the dispatcher thread. This method returns immediately even if
		/// it happens to be called on the dispatcher thread.
		/// </summary>
		/// <param name="callback">Code to execute</param>
		/// <returns></returns>
		public bool TryBeginInvoke(Action callback) {
			try {
				BeginInvoke(callback);
				return true;
			}
			catch (TaskCanceledException) {
				return false;
			}
		}

		/// <summary>
		/// Executes code on the dispatcher thread
		/// </summary>
		/// <typeparam name="T">Return type</typeparam>
		/// <param name="callback">Code to execute</param>
		/// <returns></returns>
		public abstract T Invoke<T>(Func<T> callback);

		/// <summary>
		/// Executes code on the dispatcher thread
		/// </summary>
		/// <typeparam name="T">Return type</typeparam>
		/// <param name="callback">Code to execute</param>
		/// <param name="result">Result if successful</param>
		/// <returns></returns>
		public bool TryInvoke<T>(Func<T> callback, out T result) {
			try {
				result = Invoke(callback);
				return true;
			}
			catch (TaskCanceledException) {
				result = default!;
				return false;
			}
		}

		/// <summary>
		/// Executes code on the dispatcher thread
		/// </summary>
		/// <param name="callback">Code to execute</param>
		public void Invoke(Action callback) => Invoke<object?>(() => { callback(); return null; });

		/// <summary>
		/// Executes code on the dispatcher thread
		/// </summary>
		/// <param name="callback">Code to execute</param>
		/// <returns></returns>
		public bool TryInvoke(Action callback) => TryInvoke<object?>(() => { callback(); return null; }, out _);
	}
}