Remote sync of webdav

lib/services/db_schema.dart

@@ -1,10 +1,8 @@
 const createVehiclesTableSql = '''
   CREATE TABLE vehicles (
     id TEXT PRIMARY KEY,
-    make TEXT NOT NULL,
-    model TEXT NOT NULL,
-    color TEXT NOT NULL,
-    license_plate TEXT NOT NULL,
+    vin TEXT NOT NULL,
+    nickname TEXT,
     updated_at INTEGER NOT NULL,
     deleted_at INTEGER,
     dirty INTEGER NOT NULL DEFAULT 1
@@ -30,15 +28,33 @@ const createFuelEntriesTableSql = '''
 const createFuelEntriesIndexSql =
     'CREATE INDEX idx_fuel_entries_vehicle_id ON fuel_entries(vehicle_id)';
 
+/// Selects fuel entries whose receipt photo still needs uploading to
+/// Drive. Deliberately requires `receipt_drive_file_id IS NULL`, not just
+/// "has a local path": once a row is uploaded, its local copy may still be
+/// kept around (see the "keep photos on this phone" setting) — matching on
+/// the local path alone would re-upload that same photo as a duplicate
+/// Drive file on every subsequent sync.
+const pendingReceiptUploadWhereClause = 'dirty = 1 AND receipt_image_path IS NOT NULL '
+    'AND receipt_drive_file_id IS NULL AND deleted_at IS NULL';
+
 /// Merges attached `remote_db` rows into `main` (the live local database):
 /// any remote row that's new to us, or newer than our copy, replaces ours.
 /// Rows this doesn't touch — including our own not-yet-pushed edits — are
 /// left alone, since the WHERE clause only matches rows remote should win;
 /// no separate "keep local" statement is needed.
+///
+/// Merges on `id` (the hidden, immutable identifier), not `vin` — VIN is
+/// user-editable, so it can't be relied on as a stable merge key. VIN
+/// uniqueness among active vehicles is enforced at the app layer instead
+/// (see `DatabaseService.vinExists`), not by a database constraint here,
+/// since two devices could in principle each independently add a vehicle
+/// with the same VIN while offline; that's an accepted rare-conflict edge
+/// case (see the "field-level conflicts aren't merged" caveat in the
+/// README) rather than something this merge statement tries to resolve.
 const mergeVehiclesSql = '''
   INSERT OR REPLACE INTO main.vehicles
-    (id, make, model, color, license_plate, updated_at, deleted_at, dirty)
-  SELECT r.id, r.make, r.model, r.color, r.license_plate, r.updated_at, r.deleted_at, 0
+    (id, vin, nickname, updated_at, deleted_at, dirty)
+  SELECT r.id, r.vin, r.nickname, r.updated_at, r.deleted_at, 0
   FROM remote_db.vehicles r
   LEFT JOIN main.vehicles l ON l.id = r.id
   WHERE l.id IS NULL OR r.updated_at > l.updated_at