# -*- coding: utf-8; -*-
"""
Copyright (c) 2018 Rolf Hempel, rolf6419@gmx.de

This file is part of the PlanetarySystemStacker tool (PSS).
https://github.com/Rolf-Hempel/PlanetarySystemStacker

PSS 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.

This program 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 PSS.  If not, see <http://www.gnu.org/licenses/>.

Part of this module (in class "AlignmentPointEditor" was copied from
https://stackoverflow.com/questions/35508711/how-to-enable-pan-and-zoom-in-a-qgraphicsview

"""

# The following statement is necessary so that the dependent PSS modules are found when installed
# from PyPI under site_packages.
import sys, os
sys.path.insert(0, os.path.dirname(__file__))

import getpass
import platform
from os import remove
from pathlib import Path
from sys import exit, argv

import cv2
import matplotlib
matplotlib.use('Agg')
import numpy as np
import psutil
from PyQt5 import QtWidgets, QtCore, QtGui
from numpy import uint8, uint16
import scipy
import astropy
import skimage
import pip

from alignment_point_editor import AlignmentPointEditorWidget
from alignment_points import AlignmentPoints
from configuration import Configuration
from configuration_editor import ConfigurationEditor
from display_quickstart import DisplayQuickstart
from exceptions import NotSupportedError
from frame_selector import FrameSelectorWidget
from frame_viewer import FrameViewerWidget
from frames import Frames
from job_editor import JobEditor, FileDialog
from main_gui import Ui_MainWindow
from miscellaneous import Miscellaneous
from postproc_editor import PostprocEditorWidget
from rectangular_patch_editor import RectangularPatchEditorWidget
from shift_distribution_viewer import ShiftDistributionViewerWidget
from workflow import Workflow
from pss_console import PssConsole

QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling, True)
os.environ["QT_AUTO_SCREEN_SCALE_FACTOR"] = "1"


class DisplayImage(QtWidgets.QGraphicsView):
    """
    This is an auxiliary class for debugging purposes. It opens a separate window where images
    can be displayed and updated during the computational steps. Activities are triggered from the
    workflow thread using signals.
    """

    def __init__(self):
        """
        Initialize the display window with a standard position and size. The window is resized later
        as required by the images to be displayed.
        """
        super().__init__()
        self.title = 'PyQt5 image'
        self.setWindowTitle(self.title)
        self.left = 100
        self.top = 100
        self.width = 640
        self.height = 480
        self.setGeometry(self.left, self.top, self.width, self.height)

        # Create the window scene and add a (so far undefined) photo object to it.
        self._scene = QtWidgets.QGraphicsScene()
        self._photo = QtWidgets.QGraphicsPixmapItem()
        self._scene.addItem(self._photo)
        self.setScene(self._scene)
        self.show()

    def convert_image_to_pixmap(self, image):
        """
        Convert a color or monochrome image (stored as a Numpy array of type uint8 or uint16) into
        a pixmap object.

        :param image: Numpy array of type uint8 or uint16, size: (size_y, size_x [, 3])
        :return: QPixmap object holding the image
        """

        # Convert image to 8bit if necessary.
        if image.dtype == uint16:
            image_uint8 = (image / 256.).astype(uint8)
        elif image.dtype == uint8:
            image_uint8 = image
        else:
            raise NotSupportedError("Attempt to set a photo with type neither"
                                    " uint8 nor uint16")
        self.shape_y = image_uint8.shape[0]
        self.shape_x = image_uint8.shape[1]

        # The image is monochrome:
        if len(image_uint8.shape) == 2:
            qt_image = QtGui.QImage(image_uint8, self.shape_x, self.shape_y, self.shape_x,
                                    QtGui.QImage.Format_Grayscale8)
        # The image is RGB color.
        else:
            qt_image = QtGui.QImage(image_uint8, self.shape_x, self.shape_y, 3 * self.shape_x,
                                    QtGui.QImage.Format_RGB888)
        return QtGui.QPixmap(qt_image)

    def update_image(self, new_image):
        """
        Replace the image with a new one.

        :param new_image: Image, stored as a Numpy array of type uint8 or uint16,
                          size: (size_y, size_x [, 3])
        :return: -
        """

        pixmap = self.convert_image_to_pixmap(new_image)
        self._photo.setPixmap(pixmap)

        # Fit the display window to the size of the image.
        self.resize(pixmap.width()+10, pixmap.height()+10)
        self.repaint()


class PlanetarySystemStacker(QtWidgets.QMainWindow):
    """
    This is the main class of the "Planetary System Stacker" software. It implements the main GUI
    for the communication with the user. It creates the workflow thread which controls all program
    activities asynchronously.
    """

    signal_reset_masters = QtCore.pyqtSignal()
    signal_load_master_dark = QtCore.pyqtSignal(str)
    signal_load_master_flat = QtCore.pyqtSignal(str)
    signal_frames = QtCore.pyqtSignal(object)
    signal_rank_frames = QtCore.pyqtSignal()
    signal_select_frames = QtCore.pyqtSignal()
    signal_align_frames = QtCore.pyqtSignal(int, int, int, int)
    signal_set_roi = QtCore.pyqtSignal(int, int, int, int)
    signal_set_alignment_points = QtCore.pyqtSignal()
    signal_compute_frame_qualities = QtCore.pyqtSignal()
    signal_stack_frames = QtCore.pyqtSignal()
    signal_save_stacked_image = QtCore.pyqtSignal()
    signal_postprocess_image = QtCore.pyqtSignal()
    signal_save_postprocessed_image = QtCore.pyqtSignal(object)
    signal_set_go_back_activity = QtCore.pyqtSignal(object)

    def __init__(self, parent=None):
        """
        Initialize the Planetary System Stacker environment.

        :param parent: None
        """

        # The (generated) QtGui class is contained in module main_gui.py.
        QtWidgets.QWidget.__init__(self, parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        # This line is necessary to show the menubar on Linux. On Windows it does not hurt.
        self.ui.menubar.setNativeMenuBar(False)

        # Make sure that the progress widgets retain their size when hidden.
        size_policy = self.ui.label_current_progress.sizePolicy()
        size_policy.setRetainSizeWhenHidden(True)
        self.ui.label_current_progress.setSizePolicy(size_policy)
        size_policy = self.ui.progressBar_current.sizePolicy()
        size_policy.setRetainSizeWhenHidden(True)
        self.ui.progressBar_current.setSizePolicy(size_policy)

        # Create configuration object and set configuration parameters to standard values.
        self.configuration = Configuration()
        self.configuration.initialize_configuration()

        # Set the window icon to the PSS icon.
        self.setWindowIcon(QtGui.QIcon(self.configuration.window_icon))

        # Look up the location and size of the main GUI. Replace the location parameters with those
        # stored in the configuration file when the GUI was closed last time. This way, the GUI
        # memorizes its location between MPM invocations.
        x0 = self.configuration.hidden_parameters_main_window_x0
        y0 = self.configuration.hidden_parameters_main_window_y0
        width = self.configuration.hidden_parameters_main_window_width
        height = self.configuration.hidden_parameters_main_window_height
        self.setGeometry(x0, y0, width, height)
        if self.configuration.hidden_parameters_main_window_maximized:
            self.showMaximized()

        # Initialize variables.
        self.widget_saved = None

        # Write the program version into the window title.
        self.setWindowTitle(self.configuration.global_parameters_version)

        # Connect GUI events with methods of this class.
        self.ui.actionQuit.triggered.connect(self.closeEvent)
        self.ui.comboBox_back.currentTextChanged.connect(self.go_back)
        self.ui.pushButton_start.clicked.connect(self.play)
        self.ui.pushButton_pause.clicked.connect(self.pause)
        self.ui.pushButton_next_job.clicked.connect(self.go_next)
        self.ui.pushButton_quit.clicked.connect(self.close)
        self.ui.box_automatic.stateChanged.connect(self.automatic_changed)
        self.ui.actionLoad_video_directory.triggered.connect(self.load_video_directory)
        self.ui.actionSave.triggered.connect(self.save_result)
        self.ui.actionSave_as.triggered.connect(self.save_result_as)
        self.ui.actionEdit_configuration.triggered.connect(self.edit_configuration)
        self.ui.actionLoad_config.triggered.connect(self.load_config_file)
        self.ui.actionSave_config.triggered.connect(self.save_config_file)
        self.ui.actionDe_activate_master_frames.triggered.connect(self.reset_masters)
        self.ui.actionLoad_master_dark_frame.triggered.connect(self.load_master_dark)
        self.ui.actionLoad_master_flat_frame.triggered.connect(self.load_master_flat)
        self.ui.actionCreate_new_master_dark_frame.triggered.connect(self.create_master_dark)
        self.ui.actionCreate_new_master_flat_frame.triggered.connect(self.create_master_flat)
        self.ui.actionAbout.triggered.connect(self.about_pss)
        self.ui.actionShow_Quickstart.setChecked(self.configuration.global_parameters_display_quickstart)
        self.ui.actionShow_Quickstart.triggered.connect(self.show_quickstart)

        # Create the workflow thread and start it.
        self.thread = QtCore.QThread()
        self.workflow = Workflow(self)
        self.workflow.setParent(None)
        self.workflow.moveToThread(self.thread)
        self.workflow.master_dark_created_signal.connect(self.master_dark_created)
        self.workflow.master_flat_created_signal.connect(self.master_flat_created)
        self.workflow.calibration.report_calibration_error_signal.connect(
            self.report_calibration_error)
        self.workflow.work_next_task_signal.connect(self.work_next_task)
        self.workflow.report_error_signal.connect(self.report_error)
        self.workflow.abort_job_signal.connect(self.next_job_after_error)
        self.workflow.work_current_progress_signal.connect(self.set_current_progress)
        self.workflow.set_main_gui_busy_signal.connect(self.gui_set_busy)
        self.workflow.set_status_bar_signal.connect(self.write_status_bar)
        self.workflow.create_image_window_signal.connect(self.create_image_window)
        self.workflow.update_image_window_signal.connect(self.update_image_window)
        self.workflow.terminate_image_window_signal.connect(self.terminate_image_window)
        self.thread.start()

        # Connect signals to start activities on the workflow thread (e.g. in method
        # "work_next_task").
        self.signal_reset_masters.connect(self.workflow.calibration.reset_masters)
        self.signal_load_master_dark.connect(self.workflow.calibration.load_master_dark)
        self.signal_load_master_flat.connect(self.workflow.calibration.load_master_flat)
        self.signal_frames.connect(self.workflow.execute_frames)
        self.signal_rank_frames.connect(self.workflow.execute_rank_frames)
        self.signal_select_frames.connect(self.workflow.execute_set_index_translation_table)
        self.signal_align_frames.connect(self.workflow.execute_align_frames)
        self.signal_set_roi.connect(self.workflow.execute_set_roi)
        self.signal_set_alignment_points.connect(self.workflow.execute_set_alignment_points)
        self.signal_compute_frame_qualities.connect(self.workflow.execute_compute_frame_qualities)
        self.signal_stack_frames.connect(self.workflow.execute_stack_frames)
        self.signal_save_stacked_image.connect(self.workflow.execute_save_stacked_image)
        self.signal_postprocess_image.connect(self.workflow.execute_postprocess_image)
        self.signal_save_postprocessed_image.connect(self.workflow.execute_save_postprocessed_image)
        self.signal_set_go_back_activity.connect(self.change_go_back_activity)

        # Initialize status variables
        self.automatic = self.ui.box_automatic.isChecked()
        self.busy = False
        self.pause = False
        self.job_number = 0
        self.job_index = 0
        self.jobs = []
        self.activities = ['Previous job', 'Read frames', 'Rank frames', 'Align frames',
                           'Select stack size', 'Set ROI', 'Set alignment points',
                           'Compute frame qualities', 'Stack frames', 'Save stacked image',
                           'Postprocessing', 'Save postprocessed image', 'Next job']
        self.activity = 'Read frames'
        self.error_occurred = False

        # Initialize the "backwards" combobox: The user can only go back to those program steps
        # which have been executed already.
        self.set_previous_actions_button()

        # Deactivate GUI elements which do not make sense yet.
        self.activate_gui_elements(
            [self.ui.box_automatic, self.ui.comboBox_back, self.ui.pushButton_start,
             self.ui.pushButton_pause,
             self.ui.pushButton_next_job, self.ui.actionSave, self.ui.actionSave_as,
             self.ui.actionLoad_postproc_config, self.ui.actionSave_postproc_config,
             self.ui.actionEdit_postproc_config], False)
        self.show_current_progress_widgets(False)
        self.show_batch_progress_widgets(False)

        # If the configuration was not read in from a previous run (i.e. only default values have
        # been set so far), open the configuration editor GUI to let the user make adjustments if
        # necessary.
        if not self.configuration.config_file_exists:
            # Tell the user to begin with changing / confirming config parameters.
            self.write_status_bar(
                'Adapt configuration to your needs and / or confirm by pressing "OK".', 'red')
            self.edit_configuration()

        else:
            # Tell the user to begin with specifying jobs to be executed.
            self.write_status_bar(
                "Specify video(s) or dir(s) with image files to be stacked, or single image "
                "files for postprocessing (menu: File / Open).", 'red')

        # Show the quickstart guide (if checkbox has not been de-activated.
        if self.configuration.global_parameters_display_quickstart:
            self.display_widget(DisplayQuickstart(self, self.configuration))

        # Initialize objects.
        self.image_window = None

    @QtCore.pyqtSlot()
    def show_quickstart(self):
        """
        If the user requests to re-activate the quickstart guide display at startup, change the
        corresponding gobal parameter.

        :return:
        """

        self.configuration.global_parameters_display_quickstart = \
            self.ui.actionShow_Quickstart.isChecked()

    @QtCore.pyqtSlot()
    def create_image_window(self):
        """
        On request of the workflow thread open a separate window for displaying images in debugging.

        :return: -
        """
        self.image_window = DisplayImage()

    @QtCore.pyqtSlot(object)
    def update_image_window(self, image):
        """
        Replace the image in the image window with a new one sent from the workflow thread.

        :param image: Numpy array of type uint8 or uint16, size: (size_y, size_x [, 3])
        :return: -
        """
        self.image_window.update_image(image)

    @QtCore.pyqtSlot()
    def terminate_image_window(self):
        """
        Close the separate image window on request of the workflow thread.

        :return: -
        """
        del self.image_window

    def automatic_changed(self):
        """
        If the user checks / unchecks the "Automatic" checkbox, change the corresponding status
        variable.

        :return: -
        """

        self.automatic = not self.automatic

    def edit_configuration(self):
        """
        This method is invoked by selecting the "edit stacking config" menu entry.

        :return: -
        """

        # Display the configuration editor widget in the central QFrame.
        self.display_widget(ConfigurationEditor(self))

    def change_go_back_activity(self, phases):
        """
        This method is triggered in the configuration editor if at least one parameter has been
        changed. In this case it may be necessary to reset the workflow to an earlier phase. This
        phase is set as the current activity, and later phases are deleted from the "go back"
        button list.

        :param phases: List of phases after which the workflow has to be invalidated. The
                       earliest phase on the list is relevant.
        :return: -
        """

        # Include the current activity in the list to make sure that the workflow will not jump to
        # a phase which is not yet prepared.
        phases.append(self.activity)

        # Reset the position in the workflow.
        earliest_phase = self.activities[min([self.activities.index(item) for item in phases])]

        # Only if parameters are changed later in the workflow, write a message to the protocol.
        if self.configuration.global_parameters_protocol_level > 1 and self.activity != 'Read frames':
            # If the attached logfile has been closed, re-open it.
            if self.workflow.attached_log_file is not None:
                if self.configuration.global_parameters_store_protocol_with_result and \
                        self.workflow.attached_log_file.closed:
                    try:
                        self.workflow.attached_log_file = open(self.workflow.attached_log_name, 'a')
                    except:
                        pass
            Miscellaneous.protocol(
                "+++ Parameter change: all phases after '" + earliest_phase + "' are invalidated +++",
                self.workflow.attached_log_file, precede_with_timestamp=True)

        # Reset the position in the workflow, and update the "go back" button list.
        self.activity = earliest_phase
        self.set_previous_actions_button()

    def display_widget(self, widget, display=True):
        """
        Display a widget in the central main GUI location, or remove it from there.

        :param widget: Widget object to be displayed.
        :param display: If "True", display the widget. If "False", remove the current widget from
                        the GUI.
        :return: -
        """

        if display:
            if self.widget_saved:
                self.ui.verticalLayout_2.removeWidget(self.widget_saved)
                self.widget_saved.deleteLater()
                self.widget_saved.close()
            self.widget_saved = widget
            self.ui.verticalLayout_2.insertWidget(0, widget)
            self.ui.verticalLayout_2.setStretch(1, 0)
        else:
            if self.widget_saved:
                self.ui.verticalLayout_2.removeWidget(self.widget_saved)
                self.widget_saved.deleteLater()
                self.widget_saved.close()
                self.widget_saved = None

    def load_config_file(self):
        """
        Load a stacking configuration file (extension ".pss").
        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        filename = QtWidgets.QFileDialog.getOpenFileName(self, "Load configuration file",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "*.pss", options=options)
        file_name = filename[0]

        # If a valid file was selected, read parameters from the file and open the configuration
        # editor.
        if file_name != '':
            # Read configuration parameters from the selected file.
            self.configuration.read_config(file_name=file_name)
            # Remember the current directory for next file dialog.
            self.configuration.current_dir = str(Path(file_name).parents[0])
            self.display_widget(ConfigurationEditor(self))

            if self.configuration.global_parameters_protocol_level > 1 and \
                    self.configuration.global_parameters_version_imported_from != \
                    self.configuration.global_parameters_version:
                Miscellaneous.protocol("+++ Importing configuration from older version: " +
                                self.configuration.global_parameters_version_imported_from + " +++",
                                self.workflow.attached_log_file)

    def save_config_file(self):
        """
        Save all stacking parameters in a configuration file.

        :return: -
        """

        # Open the file chooser.
        options = QtWidgets.QFileDialog.Options()
        filename = QtWidgets.QFileDialog.getSaveFileName(self, "Save configuration file",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "Config file (*.pss)",
                                                 options=options)

        # Store file only if the chooser did not return with a cancel.
        file_name = filename[0]
        if file_name != "":
            my_file = Path(file_name)

            # Remember the current directory for next file dialog.
            self.configuration.hidden_parameters_current_dir = str(my_file.parents[0])

            # If the config file exists, delete it first.
            if my_file.is_file():
                remove(str(my_file))
            self.configuration.write_config(file_name=str(my_file))

    def load_video_directory(self):
        """
        This method is invoked by selecting "Open" from the "file" menu.

        :return: -
        """

        # Open the job editor widget.
        self.display_widget(JobEditor(self))

    def reset_masters(self):
        """
        This method is invoked by selecting "Reset master frames" from the "Calibration" menu. The
        signal is caught on the workflow thread, where the method "execute_reset_masters" is
        executed.

        :return: -
        """

        self.signal_reset_masters.emit()
        if self.configuration.global_parameters_protocol_level > 0:
            Miscellaneous.protocol("+++ De-activating master dark / flat frames +++",
                                   self.workflow.attached_log_file)

    def create_master_dark(self):
        """
        Open a file dialog for entering a video file or image directory with dark frames. When the
        FileDialog closes, it sends a signal (with the path name as payload) to the corresponding
        slot on the workflow thread. There the actual master dark computation is performed.

        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        message = "Select a video file / a folder with image files for computing a master dark" \
                  " frame"

        file_dialog = FileDialog(self, message,
                                 self.configuration.hidden_parameters_current_dir,
                                 "Videos (*.avi *.mov *.mp4 *.ser)", options=options)
        file_dialog.setNameFilters(["Still image folder / video file (*.avi *.mov *.mp4 *.ser)"])

        # The list of strings (length 1) with the path name to the dark frames is sent by the
        # FileDialog via the signal "signal_dialog_ready".
        file_dialog.signal_dialog_ready.connect(self.workflow.execute_create_master_dark)
        file_dialog.exec_()

    @QtCore.pyqtSlot(bool)
    def master_dark_created(self, success):
        """
        Called from the workflow thread when it has created a master dark frame. This method is
        used to save the image to disk.

        :param success: A flag indicating if the dark frame was created successfully. Only if true,
                        write the resulting image to disk.
        :return: -
        """

        if success:
            options = QtWidgets.QFileDialog.Options()
            master_dark_file = QtWidgets.QFileDialog.getSaveFileName(self,
                                                 "Choose a file name for the new master dark frame",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "Images (*png *.tiff *.fits)",
                                                 options=options)

            if master_dark_file[0]:
                Frames.save_image(master_dark_file[0],
                                  self.workflow.calibration.master_dark_frame,
                                  color=self.workflow.calibration.dark_color,
                                  avoid_overwriting=False,
                                  header=self.configuration.global_parameters_version)
                # Remember the current directory for next file dialog.
                self.configuration.hidden_parameters_current_dir = \
                    str(Path(master_dark_file[0]).parents[0])
                if self.configuration.global_parameters_protocol_level > 1:
                    Miscellaneous.protocol("           The master dark frame was written to: " +
                                           str(master_dark_file[0]),
                                           self.workflow.attached_log_file,
                                           precede_with_timestamp=False)

        # Re-activate GUI elements.
        self.gui_set_busy(False)

    def load_master_dark(self):
        """
        This method is invoked by selecting "Load master dark" from the "Calibration" menu. It
        opens a file dialog for selecting a Png, Tiff or Fits file with a master dark frame.

        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        master_dark_file = QtWidgets.QFileDialog.getOpenFileName(self,
                                                 "Select image file containing a master dark frame",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "Images (*png *.tiff *.fits)", options=options)

        if master_dark_file[0]:
            self.signal_load_master_dark.emit(master_dark_file[0])
            # Remember the current directory for next file dialog.
            self.configuration.hidden_parameters_current_dir = str(
                Path(master_dark_file[0]).parents[0])
            if self.configuration.global_parameters_protocol_level > 0:
                Miscellaneous.protocol("+++ Loading master dark frame +++",
                                       self.workflow.attached_log_file)

    def create_master_flat(self):
        """
        Open a file dialog for entering a video file or image directory with flat frames. When the
        FileDialog closes, it sends a signal (with the path name as payload) to the corresponding
        slot on the workflow thread. There the actual master flat computation is performed.

        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        message = "Select a video file / a folder with image files for computing a master flat" \
                  " frame"

        file_dialog = FileDialog(self, message,
                                 self.configuration.hidden_parameters_current_dir,
                                 "Videos (*.avi *.mov *.mp4 *.ser)", options=options)
        file_dialog.setNameFilters(["Still image folder / video file (*.avi *.mov *.mp4 *.ser)"])

        # The list of strings (length 1) with the path name to the flat frames is sent by the
        # FileDialog via the signal "signal_dialog_ready".
        file_dialog.signal_dialog_ready.connect(self.workflow.execute_create_master_flat)
        file_dialog.exec_()

    @QtCore.pyqtSlot(bool)
    def master_flat_created(self, success):
        """
        Called from the workflow thread when it has created a master flat frame. This method is
        used to save the image to disk.

        :param success: A flag indicating if the dark frame was created successfully. Only if true,
                        write the resulting image to disk.
        :return: -
        """

        if success:
            options = QtWidgets.QFileDialog.Options()
            master_flat_file = QtWidgets.QFileDialog.getSaveFileName(self,
                                                 "Choose a file name for the new master flat frame",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "Images (*png *.tiff *.fits)",
                                                 options=options)

            if master_flat_file[0]:
                Frames.save_image(master_flat_file[0],
                                  self.workflow.calibration.master_flat_frame,
                                  color=self.workflow.calibration.flat_color,
                                  avoid_overwriting=False,
                                  header=self.configuration.global_parameters_version)
                # Remember the current directory for next file dialog.
                self.configuration.hidden_parameters_current_dir = str(
                    Path(master_flat_file[0]).parents[0])
                if self.configuration.global_parameters_protocol_level > 1:
                    Miscellaneous.protocol("           The master flat frame was written to: " +
                                           str(master_flat_file[0]),
                                           self.workflow.attached_log_file,
                                           precede_with_timestamp=False)

        # Re-activate GUI elements.
        self.gui_set_busy(False)

    def load_master_flat(self):
        """
        This method is invoked by selecting "Load master flat" from the "Calibration" menu. It
        opens a file dialog for selecting a Png, Tiff or Fits file with a master flat frame.

        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        master_flat_file = QtWidgets.QFileDialog.getOpenFileName(self,
                                                 "Select image file containing a master dark frame",
                                                 self.configuration.hidden_parameters_current_dir,
                                                 "Images (*png *.tiff *.fits)", options=options)

        if master_flat_file[0]:
            self.signal_load_master_flat.emit(master_flat_file[0])
            # Remember the current directory for next file dialog.
            self.configuration.hidden_parameters_current_dir = str(
                Path(master_flat_file[0]).parents[0])
            if self.configuration.global_parameters_protocol_level > 0:
                Miscellaneous.protocol("+++ Loading master flat frame +++",
                                       self.workflow.attached_log_file)

    @QtCore.pyqtSlot(str)
    def report_calibration_error(self, message):
        if self.configuration.global_parameters_protocol_level > 0:
            Miscellaneous.protocol("           " + message,
                                   self.workflow.attached_log_file, precede_with_timestamp=False)

    def go_back(self):
        """
        Repeat processing steps as specified via the choice of the "comboBox_back" button. The user
        can either repeat steps of the current job, or go back to the previous job.

        :return: -
        """

        # Get the choice of the combobox button.
        task = self.ui.comboBox_back.currentText()
        if self.configuration.global_parameters_protocol_level > 0:
            if self.workflow.attached_log_file is not None:
                if self.configuration.global_parameters_store_protocol_with_result and \
                        self.workflow.attached_log_file.closed:
                    try:
                        self.workflow.attached_log_file = open(self.workflow.attached_log_name, 'a')
                    except:
                        pass
            Miscellaneous.protocol("", self.workflow.attached_log_file,
                                   precede_with_timestamp=False)
            Miscellaneous.protocol("+++ Repeating from task: " + task + " +++",
                                   self.workflow.attached_log_file)

        # If the end of the job queue was reached, reverse the last job index increment.
        if self.job_index == self.job_number and self.job_index > 0:
            self.job_index -= 1

        # Restart from the specified task within the current job.
        if task in ['Read frames', 'Rank frames', 'Select frames', 'Align frames',
                    'Select stack size', 'Set ROI', 'Set alignment points',
                    'Compute frame qualities', 'Stack frames', 'Save stacked image',
                    'Postprocessing', 'Save postprocessed image']:
            # Make sure to remove any active interaction widget.
            self.display_widget(None, display=False)
            self.work_next_task(task)

        # Go back to the previous job and start with the first task.
        elif task == 'Previous job':
            self.job_index -= 1
            self.display_widget(None, display=False)
            self.work_next_task("Read frames")

    def play(self):
        """
        This method is invoked when the "Start / Cont." button is pressed.
        :return: -
        """

        # Start the next task.
        self.work_next_task(self.activity)

    def pause(self):
        """
        This method is invoked when the "Pause" button is pressed.
        :return: -
        """

        # If the pause flag is not yet set, append a message to the status bar.
        if not self.pause:
            self.append_status_bar(" Execution will be suspended after current phase.")
        # Set the pause flag.
        self.pause = True

    def go_next(self):
        """
        This method is invoked when the "Next Job" button is pressed.
        :return: -
        """

        self.work_next_task("Next job")

    @QtCore.pyqtSlot(str)
    def work_next_task(self, next_activity):
        """
        This is the central place where all activities are scheduled. Depending on the
         "next_activity" chosen, the appropriate activity is started on the workflow thread.

        :param next_activity: Activity to be performed next.
        :return: -
        """

        # Make sure not to process an empty job list, or a job index out of range.
        if not self.jobs or self.job_index >= self.job_number:
            return

        self.activity = next_activity

        # Deactivate the current progress widgets. They are reactivated when the workflow thread
        # sends a progress signal.
        self.show_current_progress_widgets(False)

        # If the "Pause" button was pressed during the last activity, stop the workflow.
        if self.pause:
            self.pause = False
            self.busy = False

        # Start workflow activities. When a workflow method terminates, it invokes this method on
        # the GUI thread, with "next_activity" denoting the next step in the processing chain.
        elif self.activity == "Read frames":
            # For the first activity (reading all frames from the file system) there is no
            # GUI interaction. Start the workflow action immediately.
            self.signal_frames.emit(self.jobs[self.job_index])
            self.busy = True

        elif self.activity == "Rank frames":
            if not self.automatic:
                pass

            self.signal_rank_frames.emit()
            self.busy = True

        elif self.activity == "Select frames":
            # If the dialog to mark frames to be excluded from stacking was requested, open the
            # dialog now.
            if not self.automatic and self.configuration.frames_add_selection_dialog:
                # Reset frames index translation, if active.
                if self.workflow.frames.index_translation_active:
                    self.workflow.frames.reset_index_translation()
                    self.workflow.rank_frames.reset_index_translation()

                fsw = FrameSelectorWidget(self, self.configuration, self.workflow.frames,
                                          self.workflow.rank_frames,
                                          self.workflow.attached_log_file,
                                          self.signal_select_frames)

                self.display_widget(fsw)
                fsw.listWidget.setFocus()

            else:
                # The dialog to exclude frames is not to be called. Update index translation
                # directly if required.
                self.signal_select_frames.emit()

        elif self.activity == "Align frames":

            # If manual stabilization patch selection was requested in 'Surface' mode, invoke the
            # patch editor.
            if not self.automatic and not self.configuration.align_frames_automation and \
                    self.configuration.align_frames_mode == 'Surface':
                border = self.configuration.align_frames_search_width

                # When the editor is finished, it sends a signal (last argument) to the workflow
                # thread with the four coordinate index bounds.
                rpew = RectangularPatchEditorWidget(self, self.workflow.frames.frames_mono(
                    self.workflow.rank_frames.frame_ranks_max_index)[border:-border,
                                                          border:-border],
                                        "With 'ctrl' and the left mouse button pressed, draw a "
                                        "rectangular patch to be used for frame alignment. Or just "
                                        "press 'OK / Cancel' (automatic selection).",
                                        self.signal_align_frames)

                self.display_widget(rpew)
                rpew.viewer.setFocus()

            else:
                # If all index bounds are set to zero, the stabilization patch is computed
                # automatically by the workflow thread.
                self.signal_align_frames.emit(0, 0, 0, 0)

            self.busy = True

        elif self.activity == "Select stack size":

            if not self.automatic:

                # Reset the ROI, if one was defined before.
                self.workflow.align_frames.reset_roi()

                # When the frame viewer is finished, it sends a signal which invokes this same
                # method on the main thread.
                fvw = FrameViewerWidget(self, self.workflow.configuration, self.workflow.frames,
                                        self.workflow.rank_frames, self.workflow.align_frames,
                                        self.workflow.attached_log_file,
                                        self.workflow.work_next_task_signal, "Set ROI")

                self.display_widget(fvw)
                fvw.frame_viewer.setFocus()

            else:
                # In automatic mode, nothing is to be done in the workflow thread. Start the next
                # activity on the main thread immediately.
                self.workflow.work_next_task_signal.emit("Set ROI")
            self.busy = True

        elif self.activity == "Set ROI":

            # Reset the ROI, if one was defined before.
            self.workflow.align_frames.reset_roi()

            if not self.automatic:

                # When the editor is finished, it sends a signal (last argument) to the workflow
                # thread with the four coordinate index bounds.
                rpew = RectangularPatchEditorWidget(self, self.workflow.align_frames.mean_frame,
                    "With 'ctrl' and the left mouse button pressed, draw a rectangle to set the"
                    " ROI, or just press 'OK' (no ROI).", self.signal_set_roi)

                self.display_widget(rpew)
                rpew.viewer.setFocus()

            else:
                # If all index bounds are set to zero, no ROI is selected.
                self.signal_set_roi.emit(0, 0, 0, 0)
            self.busy = True

        elif self.activity == "Set alignment points":
            # In automatic mode, compute the AP grid automatically in the workflow thread. In this
            # case, the AlignmentPoints object is created there as well.
            if self.automatic:
                self.signal_set_alignment_points.emit()
                self.busy = True
            else:
                # If the APs are created interactively, create the AlignmentPoints object here, but
                # assign it to the workflow object.
                if self.configuration.global_parameters_protocol_level > 0:
                    Miscellaneous.protocol("+++ Start creating alignment points +++",
                                           self.workflow.attached_log_file)
                # Initialize the AlignmentPoints object.
                self.workflow.my_timer.create_no_check('Initialize alignment point object')
                self.workflow.alignment_points = AlignmentPoints(self.workflow.configuration,
                     self.workflow.frames, self.workflow.rank_frames, self.workflow.align_frames,
                     progress_signal=self.workflow.work_current_progress_signal)
                self.workflow.my_timer.stop('Initialize alignment point object')
                # Open the alignment point editor.
                apew = AlignmentPointEditorWidget(self, self.workflow.configuration,
                                                  self.workflow.align_frames,
                                                  self.workflow.alignment_points,
                                                  self.signal_set_alignment_points)

                self.display_widget(apew)
                apew.viewer.setFocus()

        elif self.activity == "Compute frame qualities":
            if not self.automatic:
                pass
            self.signal_compute_frame_qualities.emit()
            self.busy = True

        elif self.activity == "Stack frames":
            if not self.automatic:
                pass
            self.signal_stack_frames.emit()
            self.busy = True

        elif self.activity == "Save stacked image":
            if self.automatic:
                self.signal_save_stacked_image.emit()
            else:
                sdv = ShiftDistributionViewerWidget(self,
                                                    self.workflow.stack_frames.shift_distribution,
                                                    self.workflow.stack_frames.shift_failure_percent,
                                                    self.signal_save_stacked_image)
                self.display_widget(sdv)
            self.busy = True

        elif self.activity == "Postprocessing":
            if self.automatic:
                self.signal_postprocess_image.emit()
            else:
                if self.configuration.global_parameters_protocol_level > 0:
                    Miscellaneous.protocol("+++ Start postprocessing +++",
                                           self.workflow.attached_log_file)
                # In interactive mode the postprocessed image is computed in the GUI thread. The
                # resulting image is sent via the "signal_save_postprocessed_image" signal.
                pew = PostprocEditorWidget(self.workflow.configuration,
                                           self.workflow.postproc_input_image,
                                           self.workflow.postproc_input_name,
                                           self.write_status_bar,
                                           self.signal_save_postprocessed_image)
                self.display_widget(pew)
                pew.frame_viewer.setFocus()
            self.busy = True

        elif self.activity == "Save postprocessed image":
            if not self.automatic:
                pass
            # This path is executed for "automatic" mode. In that case the postprocessed image
            # is available in the workflow object.
            if self.workflow.postprocessed_image is not None:
                self.signal_save_postprocessed_image.emit(self.workflow.postprocessed_image)
            # Otherwise it has been computed in the PostprocEditor on the GUI thread, and stored
            # in the postproc_data_object. If the editor was left with "cancel", the image is set
            # to None. In that case the workflow thread will not save the image.
            else:
                self.signal_save_postprocessed_image.emit(
                    self.workflow.configuration.postproc_data_object.versions[
                        self.workflow.configuration.postproc_data_object.version_selected].image)
            self.busy = True

        elif self.activity == "Next job":
            self.job_index += 1
            if self.job_index < self.job_number:
                # If the end of the queue is not reached yet, start with reading frames of next job.
                self.activity = "Read frames"
                # If an error condition was set during the current job, reset it.
                self.error_occurred = False
                if not self.automatic:
                    pass
                self.signal_frames.emit(self.jobs[self.job_index])
            else:
                # If an error occurred, do not include all phases in "Go back to" combo list. This
                # way the user cannot jump back to a phase of the aborted job which was not
                # executed.
                if self.error_occurred:
                    self.activity = "Read frames"
                    self.error_occurred = False
                # End of queue reached, give control back to the user.
                self.busy = False

        # Activate / Deactivate GUI elements depending on the current situation.
        self.update_status()

    @QtCore.pyqtSlot(str)
    def next_job_after_error(self, message):
        """
        This method is triggered by the workflow thread via a signal when an error causes a job to
        be aborted. In interactive mode a message window shows the error message and asks the user
        for confirmation. Depending on the protocol level, the error message is also written to the
        protocol (file).

        :param message: Error message to be displayed
        :return: -
        """

        # Report the error.
        self.report_error(message)

        # Set the error flag.
        self.error_occurred = True

        # Abort the current job and go to the next one.
        self.work_next_task("Next job")

    @QtCore.pyqtSlot(str)
    def report_error(self, message):
        """
        This method is triggered by the workflow thread via a signal when an error is to be
        reported. In interactive mode a message window shows the error message and asks the user
        for confirmation. Depending on the protocol level, the error message is also written to the
        protocol (file).

        :param message: Error message to be displayed
        :return: -
        """

        # Show a message box and wait for acknowledgement by the user.
        if not self.automatic:
            msg = QtWidgets.QMessageBox()
            msg.setText(message)
            msg.setIcon(QtWidgets.QMessageBox.Critical)
            msg.setWindowTitle(self.configuration.global_parameters_version)
            msg.setWindowIcon(QtGui.QIcon(self.configuration.window_icon))
            msg.setStandardButtons(QtWidgets.QMessageBox.Ok)
            msg.exec_()

        if self.configuration.global_parameters_protocol_level > 0:
            Miscellaneous.protocol(message + "\n", self.workflow.attached_log_file,)

    def save_result(self):
        """
        save the result as 16bit Png, Tiff or Fits file at the standard location.

        :return: -
        """

        Frames.save_image(self.workflow.stacked_image_name,
                          self.workflow.stack_frames.stacked_image,
                          color=self.workflow.frames.color, avoid_overwriting=False,
                          header=self.configuration.global_parameters_version)

    def save_result_as(self):
        """
        save the result as 16bit Png, Tiff or Fits file at a location selected by the user.

        :return: -
        """

        options = QtWidgets.QFileDialog.Options()
        filename, extension = QtWidgets.QFileDialog.getSaveFileName(self,
            "Save result as 16bit Png, Tiff or Fits image", self.workflow.stacked_image_name,
            "Image Files (*png *.tiff *.fits)", options=options)

        if filename and extension:
            Frames.save_image(filename, self.workflow.stack_frames.stacked_image,
                              color=self.workflow.frames.color, avoid_overwriting=False,
                              header=self.configuration.global_parameters_version)

    def place_holder_manual_activity(self, activity):
        # Ask the user for confirmation.
        quit_msg = "This is a placeholder for the manual activity " + activity + \
                   ". press OK when you want to continue with the workflow."
        QtWidgets.QMessageBox.question(self, 'Message', quit_msg,
                                       QtWidgets.QMessageBox.Yes | QtWidgets.QMessageBox.No,
                                       QtWidgets.QMessageBox.No)

    def show_current_progress_widgets(self, show):
        """
        Show or hide the GUI widgets showing the progress of the current job.

        :param show: If "True", show the widgets, otherwise hide them.
        :return: -
        """

        if show:
            self.ui.progressBar_current.show()
            self.ui.label_current_progress.show()
        else:
            self.ui.progressBar_current.hide()
            self.ui.label_current_progress.hide()

    @QtCore.pyqtSlot(str, int)
    def set_current_progress(self, activity, percent):
        """
        Triggered by signal "work_current_progress_signal" on the workflow thread, show the progress
        of the current activity in a progress bar on the main GUI.

        :param activity: Textual description of the current activity.
        :param percent: Fraction of task finished (in %)
        :return: -
        """

        self.show_current_progress_widgets(True)
        self.ui.label_current_progress.setText(activity)
        self.ui.progressBar_current.setValue(percent)

    def show_batch_progress_widgets(self, show, value=0):
        """
        Show or hide the GUI widgets showing the progress of the batch.

        :param show: If "True", show the widgets, otherwise hide them.
        :return: -
        """

        if show:
            self.ui.progressBar_batch.show()
            self.ui.progressBar_batch.setValue(value)
            self.ui.label_batch_progress.show()
        else:
            self.ui.progressBar_batch.hide()
            self.ui.label_batch_progress.hide()

    def set_previous_actions_button(self):
        """
        Initialize the "backwards" combobox: The user can only go back to those program steps
        which have been executed already.

        :return: -
        """

        standard_activities = ['Read frames', 'Rank frames', 'Select frames', 'Align frames',
                               'Select stack size', 'Set ROI', 'Set alignment points',
                               'Compute frame qualities', 'Stack frames', 'Save stacked image',
                               'Postprocessing', 'Save postprocessed image']

        # Stacking jobs start with 'Read frames', postprocessing jobs with 'Postprocessing'
        if self.workflow.activity == 'stacking':
            # If the optional frame selection dialog is not activated, remove the activity from the list.
            if not self.configuration.frames_add_selection_dialog:
                standard_activities.remove('Select frames')
            start_index = standard_activities.index('Read frames')
            if self.configuration.global_parameters_include_postprocessing:
                stop_index = standard_activities.index('Save postprocessed image')
            else:
                stop_index = standard_activities.index('Save stacked image')
        elif self.workflow.activity == 'postproc':
            start_index = standard_activities.index('Postprocessing')
            stop_index = standard_activities.index('Save postprocessed image')
        else:
            start_index = None
            stop_index = None

        self.ui.comboBox_back.currentTextChanged.disconnect(self.go_back)
        self.ui.comboBox_back.clear()
        self.ui.comboBox_back.addItem('Go back to:')

        # From second job on, add the option to go back to the previous one.
        if self.job_index > 0 and self.job_number > 1:
            self.ui.comboBox_back.addItem('Previous job')

        # Add all activities up to the current one to the combobox.
        if self.activity in standard_activities:
            self.ui.comboBox_back.addItems(
                standard_activities[start_index:standard_activities.index(self.activity) + 1])

        # At the end of a job, execution can resume all activities of the finished job.
        elif self.activity == "Next job":
            self.ui.comboBox_back.addItems(standard_activities[start_index:stop_index + 1])

        self.ui.comboBox_back.setCurrentIndex(0)
        self.ui.comboBox_back.currentTextChanged.connect(self.go_back)

    @QtCore.pyqtSlot(bool)
    def gui_set_busy(self, busy):
        """
        Set the main GUI busy / not busy, and update its status.

        :param busy: Flag indicating if the main GUI is to be set busy.
        :return: -
        """
        self.busy = busy
        self.update_status()

    def update_status(self):
        """
        Activate / Deactivate GUI elements depending on the current processing status.

        :return: -
        """

        # Depending on the current activity, the "previous action button" presents different
        # choices. One can only go back to activities which have been performed already.
        self.set_previous_actions_button()

        # While a computation is going on: Deactivate most buttons and menu entries.
        if self.busy:
            # For tasks with interactive GUI elements, activate the "Go back to:" button. During
            # the interaction, the status line shows the "busy" status, and the workflow is
            # suspended. By pressing "Go back to:", however, the user can restart from a previous
            # task.
            if self.activity in ['Align frames', 'Select frames', 'Select stack size', 'Set ROI',
                                     'Set alignment points']:
                self.activate_gui_elements([self.ui.comboBox_back], True)
            else:
                self.activate_gui_elements([self.ui.comboBox_back], False)
            self.activate_gui_elements([self.ui.pushButton_start,
                                        self.ui.pushButton_next_job, self.ui.menuFile,
                                        self.ui.menuEdit, self.ui.menuCalibrate], False)
            self.activate_gui_elements([self.ui.pushButton_pause], True)
            if self.job_index < self.job_number:
                if self.activity == 'Select frames':
                    self.write_status_bar("Select / de-select frames to be used for stacking.",
                                          "red")
                elif self.activity == 'Select stack size':
                    self.write_status_bar("Select the number / percentage of frames to be stacked.",
                                          "red")
                elif self.activity == 'Rank frames':
                    self.write_status_bar("Select / de-select frames to be used for stacking.",
                                          "red")
                else:
                    self.write_status_bar("Busy processing " + self.jobs[self.job_index].file_name,
                                          "black")

        # In manual mode, activate buttons and menu entries. Update the status bar.
        else:
            self.activate_gui_elements([self.ui.menuFile, self.ui.menuEdit, self.ui.menuCalibrate],
                                       True)
            self.activate_gui_elements([self.ui.pushButton_pause], False)
            if self.activity == "Next job":
                self.activate_gui_elements([self.ui.actionSave, self.ui.actionSave_as], True)
            else:
                self.activate_gui_elements([self.ui.actionSave, self.ui.actionSave_as], False)
            activated_buttons = []
            if self.job_index < self.job_number:
                activated_buttons.append(self.ui.pushButton_start)
            if self.job_index > 0 or self.activity != "Read frames":
                activated_buttons.append(self.ui.comboBox_back)
            if self.job_index < self.job_number - 1:
                activated_buttons.append(self.ui.pushButton_next_job)
            if activated_buttons:
                self.activate_gui_elements(activated_buttons, True)
                message = "To continue, press '" + \
                          self.button_get_description(activated_buttons[0]) + "'"
                if len(activated_buttons) > 1:
                    for button in activated_buttons[1:]:
                        message += ", or '" + self.button_get_description(button) + "'"
                message += ", define new jobs (File/Open), or exit the program with 'Quit'."
                self.write_status_bar(message, "red")
            else:
                self.write_status_bar("Load new jobs, or quit.", "red")
                # self.ui.statusBar.setStyleSheet('color: red')

        self.show_batch_progress_widgets(self.job_number > 1)
        if self.job_number > 0:
            self.ui.progressBar_batch.setValue(int(100 * self.job_index / self.job_number))

    def button_get_description(self, element):
        """
        Get the textual description of a button. Different methods must be used for "pushButton" and
        comboBoxes.

        :param element: Button object
        :return: Text written on the button (string)
        """

        try:
            description = element.text()
            return description
        except:
            pass
        try:
            description = element.currentText()
            return description
        except:
            return ""

    def activate_gui_elements(self, elements, enable):
        """
        Enable / Disable selected GUI elements.

        :param elements: List of GUI elements.
        :param enable: If "True", enable the elements; otherwise disable them.
        :return: -
        """

        for element in elements:
            element.setEnabled(enable)

    @QtCore.pyqtSlot(str, str)
    def write_status_bar(self, message, color):
        """
        Set the text in the status bar to "message".

        :param message: Text to be displayed
        :param color: Color in which the text is to be displayed (string)
        :return: -
        """

        self.ui.statusBar.showMessage(message)
        self.ui.statusBar.setStyleSheet('color: ' + color)

    def append_status_bar(self, append_message):
        """
        Append text to the current status bar message.

        :param append_message: Text to be appended.
        :return: -
        """

        self.ui.statusBar.showMessage(self.ui.statusBar.currentMessage() + append_message)

    def about_pss(self):

        USER = getpass.getuser()
        PC = platform.node()
        OS = '{0} {1} {2}'.format(platform.system(), platform.release(), platform.architecture()[0])
        PYTHON_VERSION = platform.python_version()
        QT_VERSION = QtCore.qVersion()
        CPU = psutil.cpu_count()
        MEMORY = psutil.virtual_memory()[0] / 1024 ** 3
        MATPLOTLIB_VERSION = matplotlib.__version__
        OPENCV_VERSION = cv2.__version__
        NUMPY_VERSION = np.__version__
        PSUTIL_VERSION = psutil.__version__
        SCIPY_VERSION = scipy.__version__
        SKIMAGE_VERSION = skimage.__version__
        ASTROPY_VERSION = astropy.__version__
        PIP_VERSION = pip.__version__

        CONTENT = ('''        <b>{0}</b><br><br>
        Produce a sharp image of a planetary system object (moon, sun, planets)
        from many seeing-affected frames using the "lucky imaging" technique.
        <br><br>
        The program is mainly targeted at extended objects (moon, sun),
        but it has been applied successfully to the imaging of planets as well.
        <br><br>
        Homepage: <a href='https://github.com/Rolf-Hempel/PlanetarySystemStacker'>
        https://github.com/Rolf-Hempel/PlanetarySystemStacker</a>
        <br><br>
        System overview:<br>
        PC: {2}<br>
        CPU Cores: {4}<br>
        Memory: {5:.1f} [GB]<br>
        OS: {3}<br>
        User: {1}<br>
        <br>
        Software versions used:<br>
        Python: {6}<br>
        Qt: {7}<br>
        Matplotlib: {8}<br>
        OpenCV: {9}<br>
        Numpy: {10}<br>
        Psutil: {11}<br>
        Scipy: {12}<br>
        Scikit-image: {13}<br>
        Astropy: {14}<br>
        Pip: {15}'''.format(self.configuration.global_parameters_version, USER, PC, OS, CPU, MEMORY,
                             PYTHON_VERSION,
                             QT_VERSION,
                             MATPLOTLIB_VERSION,
                             OPENCV_VERSION,
                             NUMPY_VERSION,
                             PSUTIL_VERSION,
                             SCIPY_VERSION,
                             SKIMAGE_VERSION,
                             ASTROPY_VERSION,
                             PIP_VERSION
                             ))

        msgBox = QtWidgets.QMessageBox()
        msgBox.setIcon(QtWidgets.QMessageBox.Information)
        msgBox.setWindowIcon(QtGui.QIcon(self.configuration.window_icon))
        msgBox.setText(CONTENT)
        msgBox.setWindowTitle("About PlanetarySystemStacker")
        msgBox.setStandardButtons(QtWidgets.QMessageBox.Ok)
        msgBox.exec()

    def closeEvent(self, event=None):
        """
        This event is triggered when the user closes the main window by clicking on the cross in
        the window corner, or selects 'Quit' in the file menu.

        :param event: event object
        :return: -
        """

        # Ask the user for confirmation.
        quit_msg = "Are you sure you want to exit?"
        reply = QtWidgets.QMessageBox.question(self, self.configuration.global_parameters_version,
                                               quit_msg,
                                               QtWidgets.QMessageBox.Yes | QtWidgets.QMessageBox.No,
                                               QtWidgets.QMessageBox.No)
        # Positive reply: Do it.
        if reply == QtWidgets.QMessageBox.Yes:
            if event:
                event.accept()

            # If there is an image log file still open, close it.
            if self.workflow.attached_log_file:
                self.workflow.attached_log_file.close()

            # Store the geometry of main window, so it is placed the same at next program start.
            if self.windowState() == QtCore.Qt.WindowMaximized:
                self.configuration.hidden_parameters_main_window_maximized = True
            else:
                (x0, y0, width, height) = self.geometry().getRect()
                self.configuration.hidden_parameters_main_window_x0 = x0
                self.configuration.hidden_parameters_main_window_y0 = y0
                self.configuration.hidden_parameters_main_window_width = width
                self.configuration.hidden_parameters_main_window_height = height
                self.configuration.hidden_parameters_main_window_maximized = False

            # Write the current configuration to the ".ini" file in the user's home directory.
            self.configuration.write_config()
            exit(0)
        else:
            # No confirmation by the user: Don't stop program execution.
            if event:
                event.ignore()


def main():
    # The following steps was required to get the program running on old Linux versions:
    #
    # - Add "export QT_XKB_CONFIG_ROOT=/usr/share/X11/xkb" to file .bashrc.
    #
    # - There is still a problem with fonts: PyInstaller seems to hardcode the path to fonts
    #   which do not make sense on another computer. This leads to error messages
    #   "Fontconfig error: Cannot load default config file", and a standard font is used
    #   instead.
    #
    # To run the PyInstaller, open a Terminal in PyCharm and enter
    # "pyinstaller planetary_system_stacker.spec" on Windows, or
    # "pyinstaller planetary_system_stacker_linux.spec" on Linux
    #

    # If PSS is started without command line arguments, open the GUI.
    if len(argv) <= 1:
        app = QtWidgets.QApplication(argv)
        # app.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling)
        myapp = PlanetarySystemStacker()
        myapp.show()
        exit(app.exec_())

    # If command line arguments are passed, execute PSS without a GUI.
    else:
        app = QtCore.QCoreApplication(argv)
        PssConsole()
        exit(app.exec_())

if __name__ == "__main__":
    main()