add better metadata handling

src/zona/builder.py

@@ -3,18 +3,38 @@ from zona import markdown as zmd
 from zona import util
 from pathlib import Path
 import frontmatter
-from dacite import from_dict
+from dacite import Config, from_dict, DaciteError
+from datetime import date
+from yaml import YAMLError
 
 
 def split_metadata(path: Path) -> tuple[Metadata, str]:
-    post = frontmatter.load(str(path))
-    # TODO: handle missing metadata
-    meta = post.metadata
-    # TODO: handle malformed metadata
-    metadata = from_dict(
-        data_class=Metadata,
-        data=meta,
-    )
+    """
+    Parses a file and returns parsed Metadata and its content. Defaults
+    are applied for missing fields. If there is no metadata, a Metadata
+    with default values is returned.
+
+    Raises:
+        ValueError: If the metadata block is malformed in any way.
+    """
+    try:
+        post = frontmatter.load(str(path))
+    except YAMLError as e:
+        raise ValueError(f"YAML frontmatter error in {path}: {e}")
+    raw_meta = post.metadata or {}
+    defaults = {
+        "title": util.filename_to_title(path),
+        "date": date.fromtimestamp(path.stat().st_mtime),
+    }
+    meta = {**defaults, **raw_meta}
+    try:
+        metadata = from_dict(
+            data_class=Metadata,
+            data=meta,
+            config=Config(check_types=True, strict=True),
+        )
+    except DaciteError as e:
+        raise ValueError(f"Malformed metadata in {path}: {e}")
     return metadata, post.content
 
 

src/zona/models.py

@@ -9,7 +9,7 @@ from typing import Literal
 class Metadata:
     title: str
     date: date
-    description: str
+    description: str | None
     # add more options later...