common: Add helper for string trimming

like defined in PEP 257

server/entertainment_decider/common.py

@@ -1,6 +1,7 @@
 from datetime import date, datetime
 import itertools
 import subprocess
+import sys
 from typing import (
     IO,
     Iterable,
@@ -28,6 +29,36 @@ def call(
     return proc
 
 
+# source: https://peps.python.org/pep-0257/#handling-docstring-indentation
+def trim(docstring: str) -> str:
+    """
+    Trim strings like docstrings are trimmed following PEP 257
+    """
+    if not docstring:
+        return ""
+    # Convert tabs to spaces (following the normal Python rules)
+    # and split into a list of lines:
+    lines = docstring.expandtabs().splitlines()
+    # Determine minimum indentation (first line doesn't count):
+    indent = sys.maxsize
+    for line in lines[1:]:
+        stripped = line.lstrip()
+        if stripped:
+            indent = min(indent, len(line) - len(stripped))
+    # Remove indentation (first line is special):
+    trimmed = [lines[0].strip()]
+    if indent < sys.maxsize:
+        for line in lines[1:]:
+            trimmed.append(line[indent:].rstrip())
+    # Strip off trailing and leading blank lines:
+    while trimmed and not trimmed[-1]:
+        trimmed.pop()
+    while trimmed and not trimmed[0]:
+        trimmed.pop(0)
+    # Return a single string:
+    return "\n".join(trimmed)
+
+
 def update_bool_value(
     old_value: bool, new_value: Union[bool, Literal["toggle"]]
 ) -> bool: