import wx


def main():
    # Always have  main method in your app, then you can use it if you run the
    # module stand alone or import it elsewhere
    app = wx.App()
    frame = CompWin()
    frame.Show()
    app.MainLoop()


class CompWin(wx.Frame):  # Class names should be CamelCase
    # Include *args and kwargs - you might need them
    def __init__(self, *args, **kwargs):
        # Always call super on an inherited class
        super().__init__(None, *args, **kwargs)
        self.Title = 'Shortage Sheet Compiler v0.1'

        # Avoid module wide variables unless constants (namespaces)
        self.dflist = ['Test1'], ['Test2']

        panel = MainPanel(self)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(panel)
        self.SetSizer(sizer)
        self.Center()
        self.Show()


class MainPanel(wx.Panel):
    # Frames and panels do different things (separation of concerns) so
    # put your panel(s) in a different class(es)
    # Panels hold widgets
    def __init__(self, parent, *args, **kwargs):
        super().__init__(parent, *args, **kwargs)
        self.parent = parent

        # Create widgets
        txt_update = wx.TextCtrl(self, value="Update Part:",
                                 size=(100, 20), pos=(5, 10),
                                 style=wx.TE_READONLY | wx.BORDER_NONE)
        self.combo_up = self.create_combobox()
        self.fill_combo_box()
        btn_refresh = wx.Button(self, label="Refresh")
        btn_refresh.Bind(wx.EVT_BUTTON, self.refresh_combo_box)

        # Put all widgets in sizers - essential for organising layout
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(txt_update)
        sizer.Add(self.combo_up)
        sizer.Add(btn_refresh)
        self.SetSizer(sizer)

    def create_combobox(self):  # Method names and variable are not CamelCase
        # When a widget has a complex set up, put in separate method
        combo_up = wx.ListCtrl(self, wx.ID_ANY, size=(150, 125), pos=(10, 30),
                               style=wx.LC_REPORT | wx.LC_SORT_ASCENDING)
        combo_up.InsertColumn(0, "Select a Part Number:", wx.LIST_FORMAT_RIGHT)
        combo_up.SetColumnWidth(0, 150)
        return combo_up

    def refresh_combo_box(self, event):
        wx.BeginBusyCursor()
        self.combo_up.DeleteAllItems()
        self.fill_combo_box()
        wx.EndBusyCursor()

    # Repeated code - put in a separate method
    def fill_combo_box(self):
        for part in self.parent.dflist:
            self.combo_up.Append(part)


if __name__ == '__main__':
    # see comment in main()
    main()