Implement distance range validation in expense validation service
epic-travel-expense-registration-core-services-task-003 — Add distance range validation for mileage-type expense claims. The validation service must verify that the submitted distance value falls within the configured minimum and maximum range for the organisation. Return typed validation errors distinguishing below-minimum from above-maximum cases so the UI can surface appropriate messages.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Implement as `_validateDistanceRange(ExpenseDraft draft, DistanceRangeConfig config)` returning `DistanceOutOfRange?` where DistanceOutOfRange is a sealed class with DistanceBelowMinimum and DistanceAboveMaximum variants. Store distance as integer metres (not double km) to avoid floating-point comparison bugs. Guard with `if (draft.expenseType != ExpenseType.mileage) return null;` at the top. Do not conflate range validation with the 50 km auto-approval rule — that belongs in the auto-approval edge function logic.
Testing Requirements
Unit tests using flutter_test. Parametrize tests over boundary values: (min-1 → fail below), (min → pass), (mid → pass), (max → pass), (max+1 → fail above). Also test: expense_type != mileage skips distance check; null distance on mileage type is treated as 0 (DistanceBelowMinimum). Use a test double for DistanceRangeConfig to avoid production config coupling.
Mutual exclusion rules are stored in the expense type catalogue's exclusive_groups field. If the catalogue schema or group definitions differ between HLF and Blindeforbundet, the validation service must handle multiple group configurations without hardcoding organisation-specific logic.
Mitigation & Contingency
Mitigation: Design the validation service to be purely data-driven: it reads exclusive_groups from the cached catalogue and enforces whichever groups are defined, with no hardcoded organisation names. Write parameterised unit tests covering at least 4 different catalogue configurations to verify generality.
Contingency: If an organisation requires non-standard exclusion semantics (e.g. partial exclusion within a group), introduce an exclusion_type field to the catalogue schema and extend the service, treating it as a catalogue configuration change rather than a code fork.
The attestation service subscribes to Supabase Realtime for live queue updates. On mobile, Realtime WebSocket connections can be dropped during network transitions, causing the coordinator queue to become stale without the user being aware.
Mitigation & Contingency
Mitigation: Implement connection lifecycle management: reconnect on network-change events, show a 'reconnecting' indicator when the subscription is broken, and perform a full queue refresh on reconnect rather than relying solely on delta events.
Contingency: Add a manual pull-to-refresh gesture on the attestation queue screen as a guaranteed fallback. If Realtime proves unreliable in production, switch to periodic polling (30-second interval) as a degraded but functional mode.
If a peer mentor submits a draft while offline and then submits the same claim again after connectivity is restored (thinking the first attempt failed), duplicate claims may be persisted in Supabase.
Mitigation & Contingency
Mitigation: Assign a client-generated idempotency key (UUID) to each draft at creation time. The submission service sends this key as an upsert key to Supabase, preventing duplicate inserts. The draft is marked 'submitted' locally after first successful upload.
Contingency: Implement a server-side duplicate detection trigger on the expense_claims table checking (activity_id, claimant_id, created_date) within a 24-hour window and returning the existing record ID rather than inserting a duplicate.