Move frontmatter validation into ContentMeta

omicron/ssg/output/article.py

@@ -1,7 +1,7 @@
 import logging
 from urllib.parse import urlparse
-from typing import TYPE_CHECKING, Any
-from omicron.ssg.output.content import Content
+from typing import TYPE_CHECKING, TypeAlias
+from omicron.ssg.output.content import Content, ContentMeta
 from omicron.ssg.output.file import File
 from pathlib import Path
 import omicron.ssg.markdown as md
@@ -14,22 +14,17 @@ else:
     Site = "omicron.ssg.site.Site"  # for runtime checking with beartype
 
 
+class ArticleMeta(ContentMeta):
+    pass
+
+
 class Article(Content):
-    def __init__(self, site: Site, source: Path, meta: dict[str, Any]):
-        if "tags" not in meta:
+    Meta: TypeAlias = ArticleMeta
+
+    def __init__(self, site: Site, source: Path, meta: ArticleMeta):
+        if not meta.tags:
             log.warning("no tags for article in '%s'", source)
-        super().__init__(
-            site,
-            source,
-            meta["section"],
-            meta["slug"],
-            meta["title"],
-            meta["date"],
-            meta.get("updated", None),
-            set(meta["tags"]) if "tags" in meta else None,
-            meta.get("summary", None),
-            meta.get("draft", False),
-        )
+        super().__init__(site, source, meta)
 
     def handle_reference(self, path: Path) -> Content | File:
         site = self.site

omicron/ssg/output/content.py

@@ -1,9 +1,11 @@
 import re
-from typing import TYPE_CHECKING
+from abc import ABC
+from dataclasses import dataclass, field, fields
+from typing import TYPE_CHECKING, Any, Self, TypeAlias
 from omicron.ssg.output.output import Output, OutputError, is_normalized
 from omicron.ssg.output.file import File
 from pathlib import Path
-from datetime import date
+import datetime
 
 if TYPE_CHECKING:
     from omicron.ssg.site import Site
@@ -15,37 +17,101 @@ class ContentError(OutputError):
     pass
 
 
+@dataclass(kw_only=True)
+class ContentMeta(ABC):
+    section: str
+    slug: str
+    title: str
+    date: datetime.date
+    updated: datetime.date | None = None
+    tags: set[str] = field(default_factory=set)
+    summary: str | None = None
+    draft: bool = False
+
+    @staticmethod
+    def validate_dict(data: dict[str, Any]) -> None:
+        section = data.get("section")
+        slug = data.get("slug")
+        title = data.get("title")
+        content_date = data.get("date")
+
+        if section is None:
+            raise ContentError("frontmatter must contain a section property")
+        if slug is None:
+            raise ContentError("frontmatter must contain a slug property")
+        if title is None:
+            raise ContentError("frontmatter must contain a title property")
+        if content_date is None:
+            raise ContentError("frontmatter must contain a date property")
+
+        if not isinstance(section, str):
+            raise ContentError("section frontmatter property must be a string")
+        if not isinstance(slug, str):
+            raise ContentError("slug frontmatter property must be a string")
+        if not isinstance(title, str):
+            raise ContentError("title frontmatter property must be a string")
+        if not isinstance(content_date, datetime.date):
+            raise ContentError("date frontmatter property must be a date")
+
+        updated = data.get("updated")
+        if updated is not None and not isinstance(updated, datetime.date):
+            raise ContentError("updated frontmatter property must be a date")
+
+        if "tags" in data and (
+            not isinstance(data["tags"], (list, set))
+            or not all(isinstance(tag, str) for tag in data["tags"])
+        ):
+            raise ContentError("tags frontmatter property must be a list of strings")
+
+        summary = data.get("summary")
+        if summary is not None and not isinstance(summary, str):
+            raise ContentError("summary frontmatter property must be a string")
+
+        draft = data.get("draft")
+        if draft is not None and not isinstance(draft, bool):
+            raise ContentError("draft frontmatter property must be a boolean")
+
+    @staticmethod
+    def coerce_dict(data: dict[str, Any]) -> None:
+        if "tags" in data and isinstance(data["tags"], list):
+            data["tags"] = set(data["tags"])
+
+    @classmethod
+    def reject_extra_fields(cls, data: dict[str, Any]) -> None:
+        field_names = {f.name for f in fields(cls)}
+
+        unexpected = data.keys() - field_names
+        if unexpected:
+            raise ContentError(
+                f"unexpected frontmatter field(s): {', '.join(sorted(unexpected))}"
+            )
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> Self:
+        cls.validate_dict(data)
+        cls.coerce_dict(data)
+        cls.reject_extra_fields(data)
+        return cls(**data)
+
+
 class Content(Output):
+    Meta: TypeAlias = ContentMeta
     _SECTION_RE = re.compile(r"^[a-z0-9_-]+(/[a-z0-9_-]+)*$")
 
-    def __init__(
-        self,
-        site: Site,
-        source: Path,
-        section: str,
-        slug: str,
-        title: str,
-        created: date,
-        updated: date | None = None,
-        tags: set[str] | None = None,
-        summary: str | None = None,
-        draft: bool = False,
-    ):
-        super().__init__(site, Content.build_path(section, slug))
-        if tags is None:
-            tags = set()
+    def __init__(self, site: Site, source: Path, meta: ContentMeta):
+        super().__init__(site, Content.build_path(meta.section, meta.slug))
         if not source.is_absolute():
             raise ContentError("content source path must be absolute")
         if not is_normalized(source):
             raise ContentError("content source path must be normalized")
         self.source = source
-        self.section: str = section
-        self.title: str = title
-        self.created = created
-        self.updated = updated
-        self.tags: set[str] = tags
-        self.summary: str | None = summary
-        self.draft: bool = draft
+        self.section = meta.section
+        self.title = meta.title
+        self.created = meta.date
+        self.updated = meta.updated
+        self.tags = meta.tags
+        self.summary = meta.summary
+        self.draft = meta.draft
         self.in_sitemap = True
 
     @staticmethod

omicron/ssg/output/factory.py

@@ -44,7 +44,8 @@ def create_content(site: Site, path: Path) -> Content:
     else:
         raise ContentError(f"Unhandled file type for '{path}'")
 
-    if meta["type"] == "article":
-        return Article(site, path, meta)
+    content_type = meta.pop("type", None)
+    if content_type == "article":
+        return Article(site, path, Article.Meta.from_dict(meta))
     else:
-        raise ContentError(f"Invalid type '{meta['type']}' for '{path}'")
+        raise ContentError(f"Invalid type '{content_type}' for '{path}'")