Both RegionService.GenerateCsvFileAsync and
RouteProcessingService.GenerateRouteCsvAsync wrote the same CSV
shape: header "latitude,longitude,file_path", same
OrderByDescending(Latitude).ThenBy(Longitude) ordering, same F6
numeric format. Two near-identical writers with no shared abstraction.
Extracted TileCsvWriter (instance class, no DI dependencies) plus a
TileCsvRow record bridging the per-pipeline DTOs (TileMetadata vs
TileInfo) to a single contract. The header constant, ordering rule,
and StreamWriter lifecycle now live in one place.
Both call sites collapse to a one-line projection plus a delegated
WriteAsync call. Region method becomes static (no longer references
instance state). Route method preserves its existing logger line.
Coverage:
- 7 new unit tests including a byte-for-byte equivalence test that
writes the same input via both the new TileCsvWriter and the
inlined-original code path side by side and asserts file bytes
are identical.
- Integration smoke + full suite green; route + region CSV outputs
unchanged across all existing scenarios (verified by extended-route
CSV verification step in the integration suite).
- 84/84 unit tests pass (was 77).
Side improvement: writer now respects CancellationToken mid-loop.
The pre-refactor inline code did not. Strict improvement; consistent
with every other async API in the codebase.
Co-authored-by: Cursor <cursoragent@cursor.com>
Oleksandr Bezdieniezhnykh