Build Export History List UI Component
epic-bufdir-report-export-core-backend-task-016 — Implement the export history list Flutter widget that reads from the generated_reports repository and displays past exports in reverse chronological order. Each list item shows: export date, scope label, period, format badge (CSV/PDF), file size, and a re-download button. Wire the re-download button to call the edge function re-download endpoint and trigger the file download handler. Show empty state when no exports exist for the org scope.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 8 - 48 tasks
Can start after Tier 7 completes
Implementation Notes
Use the existing design token system for all colors, typography, and spacing — do not hardcode values. The format badge color should use tokens (e.g., `AppColors.csvBadge` and `AppColors.pdfBadge`) rather than literals. Fetch the export list using the existing Supabase client instance from the app's dependency injection — do not create a new client. For re-download, call the edge function via the existing HTTP client wrapper used elsewhere in the app.
Use url_launcher's `launchUrl` with `LaunchMode.externalApplication` to open the signed URL so the OS handles the file download appropriately. Scope label formatting: for scope_level=chapter, display the scope_id resolved to a human-readable chapter name (query from existing chapter data in state); for region/national, use localised string constants. Period range formatting: derive readable label from period_from and period_to dates (e.g., 'Q1 2025' for Jan-Mar). Keep the widget stateless and manage all async state (loading, error, data) in a dedicated BLoC/Cubit or Riverpod notifier — do not use StatefulWidget for this.
Testing Requirements
Widget tests: render ExportHistoryList with a mock list of 3 exports and assert each item displays correct date, scope, format badge, and file size. Test that tapping re-download button triggers the re-download callback and shows loading indicator. Test empty state renders when list is empty. Test that a failed-status export shows 'Failed' chip and no re-download button.
Test accessibility: use flutter_test's SemanticsController to verify semantic labels on interactive elements. Integration test using a Supabase test project: fetch real records and assert they render in descending order. Test error handling: mock the re-download API to return 422 and assert the snackbar message appears. Verify VoiceOver compatibility manually on iOS device or simulator during QA.
Supabase Edge Functions have a default execution timeout. For large national-scope exports aggregating tens of thousands of activities across 1,400 chapters, the edge function may time out before completing, leaving coordinators with a failed export and no partial output.
Mitigation & Contingency
Mitigation: Optimise the aggregation SQL using pre-materialised aggregation views or RPC functions that run inside the database rather than iterating records in Deno. Profile query execution time against realistic production data volumes early. Request an elevated timeout limit from Supabase if needed. Implement progress checkpointing so the export can be resumed from the last completed aggregation batch.
Contingency: For organisations exceeding a configurable threshold (e.g. >5,000 activities), switch to an asynchronous export pattern: the edge function writes a 'pending' audit record and enqueues the job; the client polls for completion and is notified via Supabase Realtime when the file is ready.
Server-side PDF generation in a Deno Edge Function environment restricts library choices. Many popular PDF libraries require Node.js APIs not available in Deno, or produce large bundle sizes that exceed edge function limits. Choosing the wrong library could block the entire PDF generation path.
Mitigation & Contingency
Mitigation: Spike PDF library selection as the first task of this epic, evaluating at least two Deno-compatible options (e.g. pdf-lib, jsPDF with Deno compatibility shim). Test bundle size and basic rendering before committing to an implementation. Document the chosen library's constraints.
Contingency: If no suitable Deno-native PDF library is found, generate a well-structured HTML report from the edge function and use a headless Chromium service (e.g. Browserless, Gotenberg) for HTML-to-PDF conversion, or temporarily ship CSV-only export while the PDF path is resolved.
Peer mentors affiliated with multiple chapters (a documented NHF scenario) must not be double-counted in participant totals. Incorrect deduplication logic would overreport participation figures to Bufdir, which could be discovered during audit and damage organisational credibility.
Mitigation & Contingency
Mitigation: Define and document the deduplication contract explicitly before coding: deduplication is per-person per-period, not per-activity. Build dedicated unit tests with fixtures containing the exact multi-chapter membership patterns described in NHF's documentation. Have a NHF representative validate test fixture outputs against known-good manual counts.
Contingency: If deduplication logic produces results that cannot be verified against manual counts before launch, surface a deduplication warning in the export preview listing the affected peer mentor IDs, and require explicit coordinator acknowledgement before finalising the export.