enh: allow per-ad overriding of global description affixes (#416)

src/kleinanzeigen_bot/ads.py

@@ -5,6 +5,7 @@ SPDX-ArtifactOfProjectHomePage: https://github.com/Second-Hand-Friends/kleinanze
 """
 import hashlib, json, os
 from typing import Any
+from .utils import dicts
 
 
 def calculate_content_hash(ad_cfg: dict[str, Any]) -> str:
@@ -36,3 +37,51 @@ def calculate_content_hash(ad_cfg: dict[str, Any]) -> str:
     # Create sorted JSON string for consistent hashes
     content_str = json.dumps(content, sort_keys = True)
     return hashlib.sha256(content_str.encode()).hexdigest()
+
+
+def get_description_affixes(config: dict[str, Any], prefix: bool = True) -> str:
+    """Get prefix or suffix for description with proper precedence.
+
+    This function handles both the new flattened format and legacy nested format:
+
+    New format (flattened):
+        ad_defaults:
+            description_prefix: "Global Prefix"
+            description_suffix: "Global Suffix"
+
+    Legacy format (nested):
+        ad_defaults:
+            description:
+                prefix: "Legacy Prefix"
+                suffix: "Legacy Suffix"
+
+    Args:
+        config: Configuration dictionary containing ad_defaults
+        prefix: If True, get prefix, otherwise get suffix
+
+    Returns:
+        The appropriate affix string, empty string if none found
+
+    Example:
+        >>> config = {"ad_defaults": {"description_prefix": "Hello", "description": {"prefix": "Hi"}}}
+        >>> get_description_affixes(config, prefix=True)
+        'Hello'
+    """
+    # Handle edge cases
+    if not isinstance(config, dict):
+        return ""
+
+    affix_type = "prefix" if prefix else "suffix"
+
+    # First try new flattened format (description_prefix/description_suffix)
+    flattened_key = f"description_{affix_type}"
+    flattened_value = dicts.safe_get(config, "ad_defaults", flattened_key)
+    if isinstance(flattened_value, str):
+        return flattened_value
+
+    # Then try legacy nested format (description.prefix/description.suffix)
+    nested_value = dicts.safe_get(config, "ad_defaults", "description", affix_type)
+    if isinstance(nested_value, str):
+        return nested_value
+
+    return ""