Handle n+1 characters in the scrolling decorator

.gitignore

@@ -94,3 +94,6 @@ ENV/
 
 # Visual studio project files
 .vscode/
+
+# mypy cache
+.mypy_cache

bumblebee_status/core/decorators.py

@@ -1,6 +1,10 @@
 import difflib
+import logging
+
 import util.format
 
+log = logging.getLogger(__name__)
+
 
 def never(init):
     def call_init(obj, *args, **kwargs):
@@ -49,9 +53,10 @@ def scrollable(func):
         direction = widget.get("scrolling.direction", "right")
 
         if direction == "left":
-            scroll_speed = -scroll_speed
-            if start + scroll_speed <= 0:  # bounce back
+            if start - scroll_speed < 0:  # bounce back
                 widget.set("scrolling.direction", "right")
+            else:
+                scroll_speed = -scroll_speed
 
         next_start = start + scroll_speed
         if next_start + width > len(text):

tests/core/test_decorators.py

@@ -81,5 +81,14 @@ class config(unittest.TestCase):
         self.module.text = "this is a different song (0:12)"
         self.assertEqual(self.module.text[0:10], self.module.get(self.widget))
 
+    def test_n_plus_one(self):
+        self.module.text = "10 letters"
+        self.module.set("scrolling.width", 9)
+        self.assertEqual(self.module.text[0:9], self.module.get(self.widget))
+        self.assertEqual(self.module.text[1:10], self.module.get(self.widget))
+        self.assertEqual(self.module.text[0:9], self.module.get(self.widget))
+        self.assertEqual(self.module.text[1:10], self.module.get(self.widget))
+        self.assertEqual(self.module.text[0:9], self.module.get(self.widget))
+
 
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