Allow the UI to have a widget in the bottom right of the screen

This will be a help button in subiquity soon.

subiquitycore/ui/anchors.py

@@ -13,15 +13,22 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import logging
+
 from urwid import (
     Text,
     ProgressBar,
     )
+
 from subiquitycore.ui.container import (
+    Columns,
     Pile,
     WidgetWrap,
     )
 from subiquitycore.ui.utils import Padding, Color
+from subiquitycore.ui.width import widget_width
+
+log = logging.getLogger('subiquitycore.ui.anchors')
 
 
 class Header(WidgetWrap):
@@ -48,6 +55,36 @@ class StepsProgressBar(ProgressBar):
         return "{} / {}".format(self.current, self.done)
 
 
+class MyColumns(Columns):
+    # The idea is to render output like this:
+    #
+    #                  message                [ help  ]
+    # [ lpad        ][ middle        ][ rpad ][ right ]
+    #
+    # The constraints are:
+    #
+    # 1. lpad + rpad + right + message = maxcol
+    #
+    # 2. lpad and rpad are at least 1
+    #
+    # 3. right is fixed
+    #
+    # 4. if possible, lpad = rpad + right and middle is 79% of maxcol
+    #    or 76, whichever is greater.
+
+    def column_widths(self, size, focus=False):
+        maxcol = size[0]
+        right = widget_width(self.contents[3][0])
+
+        center = max(79*maxcol//100, 76)
+        lpad = (maxcol - center)//2
+        rpad = lpad - right
+        if rpad < 1:
+            rpad = 1
+        middle = maxcol - (lpad + rpad + right)
+        return [lpad, middle, rpad, right]
+
+
 class Footer(WidgetWrap):
     """ Footer widget
 
@@ -55,10 +92,9 @@ class Footer(WidgetWrap):
 
     """
 
-    def __init__(self, message, current, complete):
+    def __init__(self, message, right_icon, current, complete):
         if isinstance(message, str):
             message = Text(message)
-        message = Padding.center_79(message, min_width=76)
         progress_bar = Padding.center_60(
             StepsProgressBar(normal='progress_incomplete',
                              complete='progress_complete',
@@ -66,6 +102,6 @@ class Footer(WidgetWrap):
         status = [
             progress_bar,
             Padding.line_break(""),
-            message,
+            MyColumns([Text(""), message, Text(""), right_icon]),
         ]
         super().__init__(Color.frame_footer(Pile(status)))

subiquitycore/ui/frame.py

@@ -34,9 +34,11 @@ log = logging.getLogger('subiquitycore.ui.frame')
 
 class SubiquityCoreUI(WidgetWrap):
 
+    right_icon = Text("")
+
     def __init__(self):
         self.header = Header("")
-        self.footer = Footer("", 0, 1)
+        self.footer = Footer("", self.right_icon, 0, 1)
         self.progress_current = 0
         self.progress_completion = 0
         # After the install starts, we want to stop setting the footer
@@ -58,7 +60,9 @@ class SubiquityCoreUI(WidgetWrap):
     def set_footer(self, message):
         self._assign_contents(
             2,
-            Footer(message, self.progress_current, self.progress_completion))
+            Footer(
+                message, self.right_icon,
+                self.progress_current, self.progress_completion))
 
     @property
     def body(self):