app: moving on to a Toga tutorial (F to C conversion)

https://toga.readthedocs.io/en/stable/tutorial/tutorial-1.html
did a little adaptation of their example to make it a class, rather than
a build()

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

src/helloworld/__main__.py

@@ -2,4 +2,3 @@ from helloworld.app import main
 
 if __name__ == "__main__":
     main().main_loop()
-

src/helloworld/app.py

@@ -2,37 +2,59 @@
 My first application
 """
 import toga
-from toga.style import Pack
-from toga.style.pack import COLUMN, ROW
+# from toga.style import Pack
+from toga.style.pack import COLUMN, ROW, Pack, LEFT, RIGHT
 
 
 class HelloWorld(toga.App):
     def startup(self):
-        main_box = toga.Box(style=Pack(direction=COLUMN))
+        c_box = toga.Box()
+        f_box = toga.Box()
+        box = toga.Box()
 
-        name_label = toga.Label(
-                "Your name: ",
-                style=Pack(padding=(0, 5))
-                )
-        self.name_input = toga.TextInput(style=Pack(flex=1))
+        self.c_input = toga.TextInput(readonly=True)
+        self.f_input = toga.TextInput()
 
-        name_box = toga.Box(style=Pack(direction=ROW, padding=5))
-        name_box.add(name_label)
-        name_box.add(self.name_input)
+        c_label = toga.Label("Celcius", style=Pack(text_align=LEFT))
+        f_label = toga.Label("Farenheit", style=Pack(text_align=LEFT))
+        join_label = toga.Label("is equivalent to",
+                                style=Pack(text_align=RIGHT))
 
-        hello_button = toga.Button(
-                "Say Hello!",
-                on_press=self.say_hello,
-                style=Pack(padding=5)
-                )
+        button = toga.Button("Calculate", on_press=self.calculate)
 
-        main_box.add(name_box)
-        main_box.add(hello_button)
+        f_box.add(self.f_input)
+        f_box.add(f_label)
+
+        c_box.add(join_label)
+        c_box.add(self.c_input)
+        c_box.add(c_label)
+
+        box.add(f_box)
+        box.add(c_box)
+        box.add(button)
+
+        box.style.update(direction=COLUMN, padding=10)
+        f_box.style.update(direction=ROW, padding=5)
+        c_box.style.update(direction=ROW, padding=5)
+
+        self.c_input.style.update(flex=1)
+        self.f_input.style.update(flex=1, padding_left=210)
+        c_label.style.update(width=100, padding_left=10)
+        f_label.style.update(width=100, padding_left=10)
+        join_label.style.update(width=200, padding_left=10)
+
+        button.style.update(padding=15)
 
         self.main_window = toga.MainWindow(title=self.formal_name)
-        self.main_window.content = main_box
+        self.main_window.content = box
         self.main_window.show()
 
+    def calculate(self, widget):
+        try:
+            self.c_input.value = (float(self.f_input.value) - 32.0) * 5.0 / 9.0
+        except:
+            self.c_input.value = "???"
+
     def quit(self, widget):
         if self.on_exit is not None:
             self.on_exit()