using System;
using System.Threading;

namespace Plugin
{
    /// <summary>
    /// Result of a query to the engine. Allows to wait until the result is available.
    /// </summary>
    /// <typeparam name="T">Type of data inside the result.</typeparam>
    public interface IQueryResult<T>
    {
        /// <summary>
        /// Waits for the result, returns true if the timeout didn't expire.
        /// </summary>
        bool Join(out T result, int millisecondsTimeout = QueryResult<T>.DefaultTimeout);

        /// <summary>
        /// Triggered when the query is filled.
        /// </summary>
        event Action<T> Done;
    }

    /// <summary>
    /// Result of a query to the engine. Allows to wait until the result is available.
    /// </summary>
    /// <typeparam name="T">Type of data inside the result.</typeparam>
    public class QueryResult<T> : IQueryResult<T>
    {
        public const int DefaultTimeout = 2500;

        private readonly AbstractPlugin _plugin;
        private readonly ManualResetEvent _waitHandle = new ManualResetEvent(false);
        private T _content;

        public QueryResult(AbstractPlugin plugin)
        {
            _plugin = plugin;
        }

        public T Content
        {
            get { return _content; }
            set
            {
                _content = value;
                _waitHandle.Set();
                OnDone();
            }
        }

        public bool Join(out T result, int millisecondsTimeout = DefaultTimeout)
        {
            if (_waitHandle.WaitOne(millisecondsTimeout))
            {
                result = _content;
                return true;
            }
            result = _content;
            _plugin.ReportTimeoutFailure();
            return false;
        }

        /// <summary>
        /// Separated in a backend and the interface so we can trigger the event right away if already filled.
        /// </summary>
        private event Action<T> DoneBackend;

        /// <summary>
        /// Triggered when the query is filled.
        /// </summary>
        public event Action<T> Done
        {
            add
            {
                DoneBackend += value;

                // When already set, we trigger the event right now.
                if (_waitHandle.WaitOne(0))
                {
                    OnDone();
                }
            }
            remove { DoneBackend -= value; }
        }

        protected virtual void OnDone()
        {
            var done = DoneBackend;
            if (done != null)
            {
                done(Content);
            }
        }
    }
}