Implement file generator routing in BufdirExportService
epic-bufdir-report-export-orchestration-task-008 — Implement the internal routing logic that inspects the edge function response and the requested ExportFormat to dispatch the payload to either the PDF generation service or the CSV generation service. Return a typed FileGeneratorResult containing the download URL and MIME type. Handle the case where the edge function returns an unsupported format with a clear error.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Implement as a private _routeToFileGenerator() method in BufdirExportService to keep the interface clean. Use a Dart exhaustive switch expression (available in Dart 3): `return switch (format) { ExportFormat.pdf => await _pdfGenerator.generate(response), ExportFormat.csv => await _csvGenerator.generate(response), _ => throw BufdirUnsupportedFormatException(format) }`. Inject both PdfGenerationService and CsvGenerationService via Riverpod into BufdirExportService's constructor to allow mocking in tests. Define FileGeneratorResult as a freezed data class in its own file.
Keep BufdirUnsupportedFormatException in the shared exceptions file created in task-005.
Testing Requirements
Unit tests with flutter_test: (1) ExportFormat.pdf → PdfGenerationService.generate() called, CSV service not called, FileGeneratorResult has application/pdf, (2) ExportFormat.csv → CsvGenerationService.generate() called, PDF service not called, FileGeneratorResult has text/csv, (3) unsupported format enum value → BufdirUnsupportedFormatException thrown, (4) FileGeneratorResult fields correctly populated from generator return value. Use mockito stubs for both generator services. Test that adding a new ExportFormat without updating the switch causes a compile-time exhaustiveness warning.
The scope selector must accurately reflect each coordinator's access rights within the org hierarchy. If a coordinator can select a scope broader than their authorised access, the edge function's RLS enforcement must catch the attempt — but a permissive RLS policy or a bug in the scope resolver could allow unauthorised data to be exported.
Mitigation & Contingency
Mitigation: Implement permission enforcement at two independent layers: (1) the scope selector only renders options permitted by the user's role record, and (2) the edge function re-validates the requested scope against the user's JWT claims before executing any queries. Write integration tests that attempt to invoke the edge function with a scope beyond the user's permissions and assert rejection.
Contingency: If a permission bypass is discovered post-launch, immediately disable the export feature via the org-level feature flag while the fix is deployed. Review all audit records for exports that may have included out-of-scope data and notify affected organisations.
The export workflow has 7+ discrete states (idle, scope selected, period selected, preview loading, preview ready, confirming, exporting, complete, failed) and several conditional transitions. An incomplete BLoC state machine could allow duplicate submissions, stale preview data to be confirmed, or error states to be unrecoverable without a restart.
Mitigation & Contingency
Mitigation: Model the state machine explicitly as a sealed class hierarchy before coding. Review the state diagram against all user story acceptance criteria. Write bloc unit tests for every valid and invalid state transition, including the happy path and all documented error states.
Contingency: If the BLoC grows too complex to test reliably, decompose it into two cooperating blocs: one for configuration (scope + period selection) and one for execution (preview + confirm + export), linked by a coordinator object.