Add a confirmation dialogue when deleting activites..

..which have >0 facts.

Re #2

hamstertools/app.tcss

@@ -18,7 +18,7 @@ DataTable:focus .datatable--cursor {
     width: 50%;
 }
 
-ActivityEditScreen, ActivityMappingScreen {
+ActivityEditScreen, ActivityMappingScreen, ActivityDeleteConfirmScreen {
     align: center middle;
 }
 
@@ -62,3 +62,25 @@ ActivityMappingScreen AutoComplete {
 ActivityEditScreen Input {
     width: 60;
 }
+
+#dialog {
+    grid-size: 2;
+    grid-gutter: 1 2;
+    grid-rows: 1fr 3;
+    padding: 0 1;
+    width: 60;
+    height: 11;
+    border: thick $background 80%;
+    background: $surface;
+}
+
+#question {
+    column-span: 2;
+    height: 1fr;
+    width: 1fr;
+    content-align: center middle;
+}
+
+Button {
+    width: 100%;
+}

hamstertools/screens/hamster.py

@@ -4,7 +4,7 @@ from textual import on
 from textual.app import ComposeResult
 from textual.binding import Binding
 from textual.coordinate import Coordinate
-from textual.containers import Horizontal, Vertical
+from textual.containers import Horizontal, Vertical, Grid
 from textual.events import DescendantBlur
 from textual.screen import Screen, ModalScreen
 from textual.widgets import (
@@ -16,6 +16,7 @@ from textual.widgets import (
     Checkbox,
     TabbedContent,
     TabPane,
+    Button
 )
 
 from peewee import fn, JOIN
@@ -273,6 +274,29 @@ class ActivityMappingScreen(ModalScreen):
         self.dismiss(None)
 
 
+class ActivityDeleteConfirmScreen(ModalScreen):
+    BINDINGS = [
+        ("escape", "cancel", "Cancel"),
+    ]
+
+    def compose(self) -> ComposeResult:
+        yield Grid(
+            Label("Are you sure you want to delete this activity?", id="question"),
+            Button("Confirm", variant="error", id="confirm"),
+            Button("Cancel", variant="primary", id="cancel"),
+            id="dialog",
+        )
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        if event.button.id == "quit":
+            self.dismiss(True)
+        else:
+            self.dismiss(False)
+
+    def action_cancel(self):
+        self.dismiss(False)
+
+
 class ActivityList(ListPane):
     BINDINGS = [
         ("s", "sort", "Sort"),
@@ -384,10 +408,19 @@ class ActivityList(ListPane):
         )
 
         activity = HamsterActivity.get(id=activity_id)
-        activity.delete_instance()
 
-        # supply the row key to `remove_row` to delete the row.
-        self.table.remove_row(row_key)
+        def check_delete(delete: bool) -> None:
+            """Called when QuitScreen is dismissed."""
+            if delete:
+                activity.delete_instance()
+
+                # supply the row key to `remove_row` to delete the row.
+                self.table.remove_row(row_key)
+
+        if activity.facts.count() > 0:
+            self.app.push_screen(ActivityDeleteConfirmScreen(), check_delete)
+        else:
+            check_delete(True)
 
     def action_move_facts(self) -> None:
         row_idx: int = self.table.cursor_row