CodeTreeBuilderAsync.cs

using SteveCadwallader.CodeMaid.Model.CodeItems;
using System;
using System.ComponentModel;

namespace SteveCadwallader.CodeMaid.Model.CodeTree
{
    /// <summary>
    /// A helper class for performing code tree building in an asynchronous context.
    /// </summary>
    internal class CodeTreeBuilderAsync
    {
        #region Fields

        private readonly BackgroundWorker _bw;
        private readonly Action<SnapshotCodeItems> _callback;
        private CodeTreeRequest _pendingRequest;

        #endregion Fields

        #region Constructors

        /// <summary>
        /// Initializes a new instance of the <see cref="CodeTreeBuilderAsync" /> class.
        /// </summary>
        /// <param name="callback">The callback for results.</param>
        internal CodeTreeBuilderAsync(Action<SnapshotCodeItems> callback)
        {
            _bw = new BackgroundWorker { WorkerSupportsCancellation = true };
            _bw.DoWork += OnDoWork;
            _bw.RunWorkerCompleted += OnRunWorkerCompleted;

            _callback = callback;
        }

        #endregion Constructors

        #region Internal Methods

        /// <summary>
        /// Builds a code tree asynchronously from the specified request.
        /// </summary>
        /// <param name="request">The request.</param>
        internal void RetrieveCodeTreeAsync(CodeTreeRequest request)
        {
            if (_bw.IsBusy)
            {
                _pendingRequest = request;
                _bw.CancelAsync();
            }
            else
            {
                _pendingRequest = null;
                _bw.RunWorkerAsync(request);
            }
        }

        #endregion Internal Methods

        #region Private Methods

        /// <summary>
        /// Called when the background worker should perform its work.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">
        /// The <see cref="System.ComponentModel.DoWorkEventArgs" /> instance containing the event data.
        /// </param>
        private static void OnDoWork(object sender, DoWorkEventArgs e)
        {
            if (!(e.Argument is CodeTreeRequest request) || request.RawCodeItems == null)
            {
                return;
            }

            var codeItems = CodeTreeBuilder.RetrieveCodeTree(request);

            if (!e.Cancel)
            {
                e.Result = new SnapshotCodeItems(request.Document, codeItems);
            }
        }

        /// <summary>
        /// Called when the background worker has completed.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">
        /// The <see cref="System.ComponentModel.RunWorkerCompletedEventArgs" /> instance containing
        /// the event data.
        /// </param>
        private void OnRunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (_pendingRequest != null)
            {
                RetrieveCodeTreeAsync(_pendingRequest);
            }
            else if (e.Error == null)
            {
                if (e.Result is SnapshotCodeItems snapshot)
                {
                    _callback(snapshot);
                }
            }
        }

        #endregion Private Methods
    }
}