Define orchestrator interfaces and result types
epic-bufdir-reporting-export-core-logic-task-003 — Define the ExportOrchestrator abstract interface, ExportRequest value object, ExportResult sealed class (ExportSuccess with download artifact, ExportFailure with structured error), and PartialFailureReport for capturing sub-service errors without aborting the export.
Acceptance Criteria
Technical Requirements
Implementation Notes
Place under lib/features/bufdir_export/domain/orchestrator/. The sealed class pattern for ExportResult is critical — it forces all callers (UI, BLoC) to handle both success and failure branches at compile time, preventing silent error swallowing. DownloadArtifact wrapping Uint8List is intentional — it co-locates the file bytes with metadata needed for proper HTTP response headers or share_plus integration. ReportingPeriod should be defined as a shared value object reusable across the export domain (start: DateTime, end: DateTime) with a isValid getter (end >= start, both UTC).
Do NOT use Future
Testing Requirements
Unit tests for ExportResult sealed class pattern matching exhaustiveness. Test ExportSuccess with empty and non-empty partialFailures. Test ExportFailure for each ExportErrorCode variant. Test ExportRequest validation (null orgId, null userId, invalid period where end < start).
Test PartialFailureReport truncation at 1000 entries. Test DownloadArtifact MIME type inference per ExportFormat. No infrastructure mocks needed at this layer — pure model tests only.
Bufdir's column schema may have per-field business rules (conditional required fields, cross-field validation, organisation-specific category taxonomies) that cannot be expressed in a simple key-value mapping configuration. If the configuration model is too simple, supporting NHF's specific requirements will require hardcoded organisation logic, undermining the configuration-driven design.
Mitigation & Contingency
Mitigation: Design the column configuration schema as a full JSON document supporting field-level transformation rules, conditional expressions, and org-specific value enumerations. Validate the design against a real NHF Bufdir Excel template before implementation begins.
Contingency: If the configuration model cannot express all required rules, implement a thin transformation plugin interface where org-specific logic can be added as a named Dart class registered against the organisation ID, with the JSON config covering only the common cases.
For large organisations like NHF with potentially tens of thousands of activity records, the full export pipeline (query + map + generate + bundle + upload) may exceed Supabase Edge Function execution time limits (typically 150s), causing silent timeouts that leave audit records in a pending state indefinitely.
Mitigation & Contingency
Mitigation: Implement the orchestrator as a background Dart isolate with progress streaming rather than a synchronous Edge Function call. Use chunked processing for the query and mapping phases to reduce peak memory usage. Profile against realistic NHF data volumes in a staging environment.
Contingency: If processing time cannot be reduced below the timeout threshold, implement an asynchronous job model where the export is queued, processed in the background, and the user is notified via push notification when the download is ready — treating it as an eventual rather than synchronous operation.