#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2019 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library 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
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.ComponentModel;
using System.Windows.Forms;

using Nuclex.Support;
using Nuclex.Support.Threading;

namespace Nuclex.Windows.Forms.ViewModels {

  /// <summary>View model that can execute tasks in a background thread</summary>
  public abstract class ThreadedViewModel : Observable, IDisposable {

    #region class ViewModelThreadRunner

    /// <summary>Thread runner for the threaded view model</summary>
    private class ViewModelThreadRunner : ThreadRunner {

      /// <summary>Initializes a new thread runner for the threaded view model</summary>
      public ViewModelThreadRunner(ThreadedViewModel viewModel) {
        this.viewModel = viewModel;
      }

      /// <summary>Reports an error</summary>
      /// <param name="exception">Error that will be reported</param>
      protected override void ReportError(Exception exception) {
        this.viewModel.reportErrorFromThread(exception);
      }

      /// <summary>Called when the status of the busy flag changes</summary>
      protected override void BusyChanged() {
        this.viewModel.OnIsBusyChanged();
      }

      /// <summary>View model the thread runner belongs to</summary>
      private ThreadedViewModel viewModel;

    }

    #endregion // class ViewModelThreadRunner

    /// <summary>Initializes a new view model for background processing</summary>
    /// <param name="uiContext">
    ///   UI dispatcher that can be used to run callbacks in the UI thread
    /// </param>
    protected ThreadedViewModel(ISynchronizeInvoke uiContext = null) {
      if(uiContext == null) {
        this.uiContext = getMainWindow();
      } else {
        this.uiContext = uiContext;
      }

      this.reportErrorDelegate = new Action<Exception>(ReportError);

      this.threadRunner = new ViewModelThreadRunner(this);
    }

    /// <summary>Immediately releases all resources owned by the instance</summary>
    public virtual void Dispose() {
      if(this.threadRunner != null) {
        this.threadRunner.Dispose();
        this.threadRunner = null;
      }
    }

    /// <summary>Whether the view model is currently busy executing a task</summary>
    public bool IsBusy {
      get { return this.threadRunner.IsBusy; }
    }

    /// <summary>Reports an error to the user</summary>
    /// <param name="exception">Error that will be reported</param>
    /// <remarks>
    ///   <para>
    ///     You can use this method as a default handling method for your own error reporting
    ///     (displaying the error to the user, logging it or whatever else is appropriate).
    ///   </para>
    ///   <para>
    ///     When <see cref="RunInBackground(System.Action)" /> is used, this method will also
    ///     be called in case an exception within the asynchronously running code goes unhandled.
    ///     This choice was made because, in the context of UI code, you would wrap any
    ///     operations that might fail in a try..catch pair anyway in order to inform
    ///     the user instead of aborting the entire application.
    ///   </para>
    /// </remarks>
    protected abstract void ReportError(Exception exception);

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    protected void RunInBackground(Action action) {
      this.threadRunner.RunInBackground(action);
    }

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    protected void RunInBackground(CancellableAction action) {
      this.threadRunner.RunInBackground(action);
    }

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    /// <param name="parameter1">Parameter that will be passed to the action</param>
    protected void RunInBackground<P1>(Action<P1> action, P1 parameter1) {
      this.threadRunner.RunInBackground(action, parameter1);
    }

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    /// <param name="parameter1">Parameter that will be passed to the action</param>
    protected void RunInBackground<P1>(CancellableAction<P1> action, P1 parameter1) {
      this.threadRunner.RunInBackground(action, parameter1);
    }

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    /// <param name="parameter1">First parameter that will be passed to the action</param>
    /// <param name="parameter2">Second parameter that will be passed to the action</param>
    protected void RunInBackground<P1, P2>(Action<P1, P2> action, P1 parameter1, P2 parameter2) {
      this.threadRunner.RunInBackground(action, parameter1, parameter2);
    }

    /// <summary>Executes the specified operation in the background</summary>
    /// <param name="action">Action that will be executed in the background</param>
    /// <param name="parameter1">First parameter that will be passed to the action</param>
    /// <param name="parameter2">Second parameter that will be passed to the action</param>
    protected void RunInBackground<P1, P2>(
      CancellableAction<P1, P2> action, P1 parameter1, P2 parameter2
    ) {
      this.threadRunner.RunInBackground(action, parameter1, parameter2);
    }

    /// <summary>Cancels the currently running background operation</summary>
    protected void CancelBackgroundOperation() {
      this.threadRunner.CancelBackgroundOperation();
    }

    /// <summary>Cancels all queued and the currently running background operation</summary>
    protected void CancelAllBackgroundOperations() {
      this.threadRunner.CancelAllBackgroundOperations();
    }

    /// <summary>Whether the background operation has been cancelled</summary>
    //[Obsolete("Please use a method accepting a cancellation token instead of using this")]
    protected bool IsBackgroundOperationCancelled {
      get { return this.threadRunner.IsBackgroundOperationCancelled; }
    }

    /// <summary>Throws an exception if the background operation was cancelled</summary>
    //[Obsolete("Please use a method accepting a cancellation token instead of using this")]
    protected void ThrowIfBackgroundOperationCancelled() {
      this.threadRunner.ThrowIfBackgroundOperationCancelled();
    }

    /// <summary>Executes the specified action in the UI thread</summary>
    /// <param name="action">Action that will be executed in the UI thread</param>
    protected void RunInUIThread(Action action) {
      this.uiContext.Invoke(action, EmptyObjectArray);
    }

    /// <summary>Executes the specified action in the UI thread</summary>
    /// <param name="action">Action that will be executed in the UI thread</param>
    /// <param name="parameter1">Parameter that will be passed to the action</param>
    protected void RunInUIThread<P1>(Action<P1> action, P1 parameter1) {
      this.uiContext.Invoke(action, new object[1] { parameter1 });
    }

    /// <summary>Executes the specified action in the UI thread</summary>
    /// <param name="action">Action that will be executed in the UI thread</param>
    /// <param name="parameter1">First parameter that will be passed to the action</param>
    /// <param name="parameter2">Second parameter that will be passed to the action</param>
    protected void RunInUIThread<P1, P2>(Action<P1, P2> action, P1 parameter1, P2 parameter2) {
      this.uiContext.Invoke(action, new object[2] { parameter1, parameter2 });
    }

    /// <summary>Called when the thread runner's busy flag changes</summary>
    protected virtual void OnIsBusyChanged() {
      OnPropertyChanged(nameof(IsBusy));
    }

    /// <summary>Reports an error that occurred in the runner's background thread</summary>
    /// <param name="exception">Exception that the thread has encountered</param>
    private void reportErrorFromThread(Exception exception) {
      this.uiContext.Invoke(this.reportErrorDelegate, new object[1] { exception });
    }

    /// <summary>Finds the application's main window</summary>
    /// <returns>Main window of the application</returns>
    private static Form getMainWindow() {
      IntPtr mainWindowHandle = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;

      // We can get two things: a list of all open windows and the handle of
      // the window that the process has registered as main window. Use the latter
      // to pick the correct window from the former.
      FormCollection openForms = Application.OpenForms;
      int openFormCount = openForms.Count;
      for(int index = 0; index < openFormCount; ++index) {
        if(openForms[index].IsHandleCreated) {
          if(openForms[index].Handle == mainWindowHandle) {
            return openForms[index];
          }
        }
      }

      // No matching main window found: use the first one in good faith or fail.
      if(openFormCount > 0) {
        return openForms[0];
      } else {
        return null;
      }
    }

    /// <summary>An array of zero objects</summary>
    private static readonly object[] EmptyObjectArray = new object[0];

    /// <summary>UI dispatcher of the thread in which the view runs</summary>
    private ISynchronizeInvoke uiContext;
    /// <summary>Delegate for the ReportError() method</summary>
    private Action<Exception> reportErrorDelegate;
    /// <summary>Thread runner that manages the view model's thread</summary>
    private ViewModelThreadRunner threadRunner;

  }

} // namespace Nuclex.Windows.Forms.ViewModels