From 923a72fef676c34e9cb48a295e837a2e52893fad Mon Sep 17 00:00:00 2001
From: Andrew Hamilton <and_hamilton@yahoo.com>
Date: Mon, 24 Jan 2022 23:06:42 +1000
Subject: [PATCH] fill3: Optionally limit scroll of portals

---
 fill3/fill3/__init__.py   | 26 +++++++++++++++++++++++++-
 fill3/tests/fill3_test.py |  9 +++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/fill3/fill3/__init__.py b/fill3/fill3/__init__.py
index f7d166a..ef8bbc7 100755
--- a/fill3/fill3/__init__.py
+++ b/fill3/fill3/__init__.py
@@ -202,10 +202,14 @@ class ScrollBar:
 
 class Portal:
 
-    def __init__(self, widget, position=(0, 0), background_char=" "):
+    def __init__(self, widget, position=(0, 0), background_char=" ",
+                 is_scroll_limited=False, is_left_aligned=True, is_top_aligned=True):
         self.widget = widget
         self.position = position
         self.background_char = background_char
+        self.is_scroll_limited = is_scroll_limited
+        self.is_left_aligned = is_left_aligned
+        self.is_top_aligned = is_top_aligned
         self.last_dimensions = 0, 0
 
     def _scroll_half_pages(self, dx, dy):
@@ -225,6 +229,24 @@ class Portal:
     def scroll_right(self):
         self._scroll_half_pages(1, 0)
 
+    def limit_scroll(self, portal_dimensions, appearance_dimensions):
+        portal_width, portal_height = portal_dimensions
+        widget_width, widget_height = appearance_dimensions
+        x, y = self.position
+        if widget_width <= portal_width:
+            x = 0 if self.is_left_aligned else (widget_width - portal_width)
+        elif x < 0:
+            x = 0
+        elif x > (widget_width - portal_width):
+            x = widget_width - portal_width
+        if widget_height <= portal_height:
+            y = 0 if self.is_top_aligned else (widget_height - portal_height)
+        elif y < 0:
+            y = 0
+        elif y > (widget_height - portal_height):
+            y = widget_height - portal_height
+        return x, y
+
     def appearance_for(self, dimensions):
         width, height = dimensions
         x, y = self.position
@@ -232,6 +254,8 @@ class Portal:
             appearance = self.widget.appearance_interval((max(y, 0), y+height))
         except AttributeError:
             appearance = self.widget.appearance()[max(y, 0):y+height]
+        if self.is_scroll_limited:
+            x, y = self.limit_scroll(dimensions, appearance_dimensions(appearance))
         self.last_dimensions = dimensions
         top = [self.background_char * width] * -y if y < 0 else []
         bottom = appearance_resize([row[max(x, 0):x+width] for row in appearance],
diff --git a/fill3/tests/fill3_test.py b/fill3/tests/fill3_test.py
index b2b007c..a9139a5 100755
--- a/fill3/tests/fill3_test.py
+++ b/fill3/tests/fill3_test.py
@@ -45,6 +45,15 @@ class WidgetTests(unittest.TestCase):
         self.assert_string(portal.appearance_for((8, 3)), "        \n foobar \n        ")
         portal.position = (5, 0)
         self.assert_string(portal.appearance_for((2, 1)), "r ")
+        # limit scroll
+        portal.position = (0, 0)
+        self.assertEqual(portal.limit_scroll((1, 1), (1, 1)), (0, 0))
+        portal.position = (-1, 0)
+        self.assertEqual(portal.limit_scroll((1, 1), (1, 1)), (0, 0))
+        portal.position = (1, 0)
+        self.assertEqual(portal.limit_scroll((6, 1), (1, 1)), (0, 0))
+        portal.is_left_aligned = False
+        self.assertEqual(portal.limit_scroll((6, 1), (1, 1)), (-5, 0))
 
     def test_border_widget(self):
         contents = fill3.Filler(self.TEXT_A)