Implémentation de build_database avec transforms Polars et tables dérivées

- _load_source_frame reprend la pipeline Polars (sort, filtre donneesActuelles,
  booleans_to_strings, remplacement des noms null)
- build_database utilise write_parquet + read_parquet pour zéro-dépendance
  pyarrow (pyarrow absent du venv) et écrit atomiquement via .tmp + os.replace
- 4 tables dérivées : acheteurs_marches, titulaires_marches,
  acheteurs_departement, titulaires_departement

refs #71

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/db.py

@@ -1,28 +1,109 @@
 import logging
 import os
 from pathlib import Path
+from time import sleep
+
+import duckdb
+import polars as pl
+import polars.selectors as cs
+from polars.exceptions import ComputeError
 
 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
+
+
+def _load_source_frame(parquet_path: Path) -> pl.DataFrame:
+    """Read the source parquet and apply the row-level transforms.
+
+    Kept here (not in utils.py) so src.db has no dependency on utils.
+    Mirrors the behavior previously in utils.get_decp_data().
+    """
+    try:
+        lff: pl.LazyFrame = pl.scan_parquet(str(parquet_path))
+    except ComputeError:
+        logger.info("Lecture du parquet échouée, nouvelle tentative dans 10s...")
+        sleep(10)
+        lff = pl.scan_parquet(str(parquet_path))
+
+    lff = lff.sort(by=["dateNotification", "uid"], descending=True, nulls_last=True)
+    lff = lff.filter(pl.col("donneesActuelles")).drop("donneesActuelles")
+
+    # booleans_to_strings: true → "oui", false → "non"
+    lff = lff.with_columns(
+        pl.col(cs.Boolean)
+        .cast(pl.String)
+        .str.replace("true", "oui")
+        .str.replace("false", "non")
+    )
+
+    for col in ["acheteur_nom", "titulaire_nom"]:
+        lff = lff.with_columns(
+            pl.when(pl.col(col).is_null())
+            .then(pl.lit("[Identifiant non reconnu dans la base INSEE]"))
+            .otherwise(pl.col(col))
+            .name.keep()
+        )
+
+    return lff.collect()
+
+
+def build_database(db_path: Path, parquet_path: Path) -> None:
+    """Build the DuckDB database atomically under an exclusive lock.
+
+    Caller MUST hold the fcntl.flock on the .lock file.
+    """
+    db_path = Path(db_path)
+    parquet_path = Path(parquet_path)
+    tmp_path = db_path.with_suffix(".duckdb.tmp")
+    staging_parquet = db_path.with_suffix(".staging.parquet")
+    if tmp_path.exists():
+        tmp_path.unlink()
+
+    logger.info(f"Construction de la base DuckDB à partir de {parquet_path}...")
+    frame = _load_source_frame(parquet_path)
+
+    # Write transformed frame as parquet so DuckDB can read it natively
+    # (avoids pyarrow dependency for the Polars→DuckDB handoff)
+    frame.write_parquet(str(staging_parquet))
+    try:
+        with duckdb.connect(str(tmp_path)) as w:
+            w.execute(
+                f"CREATE TABLE decp AS SELECT * FROM read_parquet('{staging_parquet}')"
+            )
+            w.execute(
+                "CREATE TABLE acheteurs_marches AS "
+                "SELECT DISTINCT uid, objet, acheteur_id FROM decp "
+                "ORDER BY acheteur_id"
+            )
+            w.execute(
+                "CREATE TABLE titulaires_marches AS "
+                "SELECT DISTINCT uid, objet, titulaire_id FROM decp "
+                "ORDER BY titulaire_id"
+            )
+            w.execute(
+                "CREATE TABLE acheteurs_departement AS "
+                "SELECT DISTINCT acheteur_id, acheteur_nom, acheteur_departement_code "
+                "FROM decp ORDER BY acheteur_nom"
+            )
+            w.execute(
+                "CREATE TABLE titulaires_departement AS "
+                "SELECT DISTINCT titulaire_id, titulaire_nom, titulaire_departement_code "
+                "FROM decp ORDER BY titulaire_nom"
+            )
+    finally:
+        if staging_parquet.exists():
+            staging_parquet.unlink()
+
+    os.replace(tmp_path, db_path)
+    logger.info(f"Base DuckDB construite : {db_path}")