Build CSV Generation Service from Bufdir Payload
epic-bufdir-report-export-core-backend-task-008 — Implement the CSV generation service that consumes the canonical Bufdir JSON payload and produces a UTF-8 CSV file conforming to Bufdir's column layout. Each row represents one peer mentor's aggregated activity per category. Include a header row with Norwegian column labels as Bufdir expects, format dates as DD.MM.YYYY, and encode numeric fields without thousand separators. The service must return a Uint8List suitable for storage upload or direct HTTP response.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Use a StringBuffer for construction efficiency. Define the column order as a Dart const List
Add the BOM as the first three bytes before encoding the StringBuffer content: `final bom = Uint8List.fromList([0xEF, 0xBB, 0xBF])`. For the summary row, use a distinct label in the peer_mentor_name column (e.g. 'TOTALT') so it is visually distinct. Keep the service as a pure function: `Uint8List generateCsv(BufdirPayload payload)` — no I/O, no Supabase client.
Testing Requirements
Unit tests (dart:test): (1) output begins with UTF-8 BOM bytes [0xEF, 0xBB, 0xBF], (2) header row contains all required Norwegian column labels in correct order, (3) date fields are formatted DD.MM.YYYY not ISO format, (4) numeric fields contain no commas or dots, (5) a field containing a semicolon is properly double-quoted per RFC 4180, (6) empty payload produces header-only output with no exception, (7) summary row totals match sum of all data rows (arithmetic assertion), (8) output is valid UTF-8 (decoded without error), (9) CSV injection prevention: field starting with '=' is prefixed. Integration test: generate CSV from the task-006 serializer output and parse it back with a CSV parser; assert row count equals number of (peer_mentor × category) combinations in the input.
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.