Ajout de src.db.should_rebuild et ses tests

refs #71

src/db.py

@@ -0,0 +1,28 @@
+import logging
+import os
+from pathlib import Path
+
+logger = logging.getLogger("decp.info")
+
+
+def should_rebuild(db_path: Path, parquet_path: Path) -> bool:
+    """Decide whether to rebuild the DuckDB database from the source Parquet.
+
+    Rules:
+      - Rebuild if the DuckDB file does not exist.
+      - Otherwise, rebuild only if the source Parquet is newer than the DB,
+        EXCEPT in development mode without REBUILD_DUCKDB=true (dev keeps
+        a stable DB across reloads unless explicitly opted in).
+    """
+    db_path = Path(db_path)
+    parquet_path = Path(parquet_path)
+
+    if not db_path.exists():
+        return True
+
+    dev = os.getenv("DEVELOPMENT", "False").lower() == "true"
+    force = os.getenv("REBUILD_DUCKDB", "False").lower() == "true"
+    if dev and not force:
+        return False
+
+    return parquet_path.stat().st_mtime > db_path.stat().st_mtime