Add workflow step to ensure parties are in the past

.github/workflows/validate.yml

@@ -36,3 +36,7 @@ jobs:
         run: |
           shopt -s globstar
           taplo lint --schema "file://"$PWD"/schemas/party.json" data/parties/**/*.toml && taplo format --check data/parties/**/*.toml
+
+      - name: Ensure that parties are in the past
+        run: |
+          python3 tools/check_party_date.py data/parties/**/*.toml

tools/check_party_date.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+
+"""Return error code if parties are found that are not in the past.
+
+Author: Jochen Kupperschmidt
+"""
+
+from collections.abc import Iterable
+from dataclasses import dataclass
+from datetime import date
+from pathlib import Path
+import sys
+import tomllib
+
+
+@dataclass(frozen=True, slots=True)
+class Party:
+    path: Path
+    slug: str
+    title: str
+    end_on: date
+
+
+def main(filenames: list[str]) -> None:
+    if not filenames:
+        return
+
+    paths = map(Path, filenames)
+    parties = map(load_party, paths)
+    parties_not_over = select_parties_not_over(parties)
+
+    if parties_not_over:
+        print_parties_not_in_past(parties_not_over)
+        sys.exit(1)
+
+
+def load_party(path: Path) -> Party:
+    toml = path.read_text()
+    data = tomllib.loads(toml)
+
+    return Party(
+        path=path,
+        slug=data['slug'],
+        title=data['title'],
+        end_on=data['end_on'],
+    )
+
+
+def select_parties_not_over(parties: Iterable[Party]) -> list[Party]:
+    today = date.today()
+    return list(filter(lambda party: party.end_on >= today, parties))
+
+
+def print_parties_not_in_past(parties: Iterable[Party]) -> None:
+    write_error_line('Found parties not in the past:')
+    for party in parties:
+        write_error_line(f'+ "{party.title}" ends on {party.end_on}')
+        write_error_line(f'  - file: {party.path}')
+
+
+def write_error_line(text: str) -> None:
+    sys.stderr.write(f'{text}\n')
+
+
+if __name__ == '__main__':
+    filenames = sys.argv[1:]
+    main(filenames)