fCraft.BuildingCommands.UndoHandler C# (CSharp) Method

        private static void UndoHandler( Player player, Command cmd )
        {
            World playerWorld = player.World;
            if ( playerWorld == null )
                PlayerOpException.ThrowNoWorld( player );
            if ( cmd.HasNext ) {
                player.Message( "Undo command takes no parameters. Did you mean to do &H/UndoPlayer&S or &H/UndoArea&S?" );
                return;
            }

            string msg = "Undo: ";
            UndoState undoState = player.UndoPop();
            if ( undoState == null ) {
                player.MessageNow( "There is currently nothing to undo." );
                return;
            }

            // Cancel the last DrawOp, if still in progress
            if ( undoState.Op != null && !undoState.Op.IsDone && !undoState.Op.IsCancelled ) {
                undoState.Op.Cancel();
                msg += String.Format( "Cancelled {0} (was {1}% done). ",
                                     undoState.Op.Description,
                                     undoState.Op.PercentDone );
            }

            // Check if command was too massive.
            if ( undoState.IsTooLargeToUndo ) {
                if ( undoState.Op != null ) {
                    player.MessageNow( "Cannot undo {0}: too massive.", undoState.Op.Description );
                } else {
                    player.MessageNow( "Cannot undo: too massive." );
                }
                return;
            }

            // no need to set player.drawingInProgress here because this is done on the user thread
            Logger.Log( LogType.UserActivity,
                        "Player {0} initiated /Undo affecting {1} blocks (on world {2})",
                        player.Name,
                        undoState.Buffer.Count,
                        playerWorld.Name );

            msg += String.Format( "Restoring {0} blocks. Type &H/Redo&S to reverse.",
                                  undoState.Buffer.Count );
            player.MessageNow( msg );

            var op = new UndoDrawOperation( player, undoState, false );
            op.Prepare( new Vector3I[0] );
            op.Begin();
        }