begin migrating code that can be reused from first iteration of this idea

portable_computing_toolkit_installer/validators/location_validator.py

@@ -0,0 +1,67 @@
+from PyQt5 import QtCore, QtGui, QtWidgets
+import psutil
+import os
+import pathlib
+
+
+class Location_Validator(QtGui.QValidator):
+    def __init__(self, parent=None):
+        super().__init__(parent)
+
+    def _onNTFSDrive(self, location):
+        """Tests if location is a path on an NTFS-formatted drive.  Returns True if path is on NTFS-formatted drive.
+
+        Arguments:
+            location {str} -- A string representing a folder path
+        """
+        match = [drive for drive in psutil.disk_partitions() if (drive.device == pathlib.Path(location).anchor and drive.fstype == "NTFS")]
+        if not match:
+            QtWidgets.QMessageBox(
+                icon=QtWidgets.QMessageBox.Critical,
+                parent=self.parent(),
+                text=f"{pathlib.Path(location).anchor} is not an NTFS-formatted volume.  Please reformat your drive to NTFS or pick an install path on a different volume"
+            ).show()
+            return False
+        else:
+            return True
+
+    def validate(self, input_, pos):
+        """Called by Portable_CS_Toolkit_Installer via QtWidget.QLineEdit.TextChanged signal to validate installation location input of user
+
+        Arguments:
+            input_ {str} -- The text entered in the installation location QLineEdit widget
+            pos {int} -- The current location of the cursor in the QLineEdit widget
+        """
+        if input_.endswith(r":"):
+            return (
+                QtGui.QValidator.Intermediate,
+                input_,
+                pos,
+            )  # bugfix.  _onNTFSDrive triggers when typing the : in a drive name e.g. C:\
+
+        # because this class method is invoked via signal, it cannot handle python exceptions
+        # testing writability in Python is difficult and involves actually writing a temporary file
+        # to the directory, however, if that fails and raises an exception, it happens in Qt/C++ world
+        # and the python interpreter can't catch it, the program just crashes without any output,
+        # therefore, we will use Qt to do checking
+        input_ = os.path.expandvars(input_)  # expand any environment variables in input
+        location = QtCore.QFileInfo(input_)
+        if location.exists() and location.isDir():
+
+            if input_ and not self._onNTFSDrive(input_):
+                # clear the location, reset cursor, but allow continued edits
+                return (QtGui.QValidator.Intermediate, "", 0)
+
+            test_file = QtCore.QTemporaryFile(input_ + r"\testXXXXXX.tmp")
+
+            if test_file.open(QtCore.QIODevice.ReadWrite):
+                test_file.close()
+                test_file.remove()
+                return (QtGui.QValidator.Acceptable, input_, pos)
+            else:
+                return (QtGui.QValidator.Intermediate, input_, pos)
+
+        else:
+            # I wanted to return invalid, but that would prevent input of anything not instantly acceptable
+            # or editing something acceptable to something else acceptable, passing through an invalid on the way
+            return (QtGui.QValidator.Intermediate, input_, pos)