python/utils: add add_visual_margin() text decoration utility

>>> print(add_visual_margin(msg, width=72, name="Commit Message"))
┏━ Commit Message ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
┃ add_visual_margin() takes a chunk of text and wraps it in a visual
┃ container that force-wraps to a specified width. An optional title
┃ label may be given, and any of the individual glyphs used to draw the
┃ box may be replaced or specified as well.
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220321201618.903471-2-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

python/qemu/utils/__init__.py

@@ -15,14 +15,18 @@
 # the COPYING file in the top-level directory.
 #
 
+import os
 import re
+import shutil
+import textwrap
 from typing import Optional
 
 # pylint: disable=import-error
 from .accel import kvm_available, list_accel, tcg_available
 
 
 __all__ = (
+    'add_visual_margin',
     'get_info_usernet_hostfwd_port',
     'kvm_available',
     'list_accel',
@@ -43,3 +47,77 @@ def get_info_usernet_hostfwd_port(info_usernet_output: str) -> Optional[int]:
         if match is not None:
             return int(match[1])
     return None
+
+
+# pylint: disable=too-many-arguments
+def add_visual_margin(
+        content: str = '',
+        width: Optional[int] = None,
+        name: Optional[str] = None,
+        padding: int = 1,
+        upper_left: str = '┏',
+        lower_left: str = '┗',
+        horizontal: str = '━',
+        vertical: str = '┃',
+) -> str:
+    """
+    Decorate and wrap some text with a visual decoration around it.
+
+    This function assumes that the text decoration characters are single
+    characters that display using a single monospace column.
+
+    ┏━ Example ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+    ┃ This is what this function looks like with text content that's
+    ┃ wrapped to 66 characters. The right-hand margin is left open to
+    ┃ accommodate the occasional unicode character that might make
+    ┃ predicting the total "visual" width of a line difficult. This
+    ┃ provides a visual distinction that's good-enough, though.
+    ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+    :param content: The text to wrap and decorate.
+    :param width:
+        The number of columns to use, including for the decoration
+        itself. The default (None) uses the the available width of the
+        current terminal, or a fallback of 72 lines. A negative number
+        subtracts a fixed-width from the default size. The default obeys
+        the COLUMNS environment variable, if set.
+    :param name: A label to apply to the upper-left of the box.
+    :param padding: How many columns of padding to apply inside.
+    :param upper_left: Upper-left single-width text decoration character.
+    :param lower_left: Lower-left single-width text decoration character.
+    :param horizontal: Horizontal single-width text decoration character.
+    :param vertical: Vertical single-width text decoration character.
+    """
+    if width is None or width < 0:
+        avail = shutil.get_terminal_size(fallback=(72, 24))[0]
+        if width is None:
+            _width = avail
+        else:
+            _width = avail + width
+    else:
+        _width = width
+
+    prefix = vertical + (' ' * padding)
+
+    def _bar(name: Optional[str], top: bool = True) -> str:
+        ret = upper_left if top else lower_left
+        if name is not None:
+            ret += f"{horizontal} {name} "
+
+        filler_len = _width - len(ret)
+        ret += f"{horizontal * filler_len}"
+        return ret
+
+    def _wrap(line: str) -> str:
+        return os.linesep.join(
+            textwrap.wrap(
+                line, width=_width - padding, initial_indent=prefix,
+                subsequent_indent=prefix, replace_whitespace=False,
+                drop_whitespace=True, break_on_hyphens=False)
+        )
+
+    return os.linesep.join((
+        _bar(name, top=True),
+        os.linesep.join(_wrap(line) for line in content.splitlines()),
+        _bar(None, top=False),
+    ))