Scaffold Distance Input Field widget skeleton
epic-mileage-reimbursement-entry-user-interface-task-001 — Create the base StatelessWidget class for DistanceInputFieldWidget in Flutter with a numeric TextFormField, a numeric keyboard input type, an onChanged callback signature, and the initial widget constructor accepting an optional prefillValue double and required onChanged callback. Wire the widget into the design token theme system.
Acceptance Criteria
Technical Requirements
Implementation Notes
Keep this widget strictly presentational (StatelessWidget). Do not introduce BLoC or Riverpod at this stage — those are added in later tasks. Use a local TextEditingController only if needed for prefill; if so, wrap in a thin StatefulWidget shell. Reference the existing AppTextField widget to ensure design token wiring is consistent with the rest of the app.
Use FilteringTextInputFormatter.allow(RegExp(r'[0-9.]')) to restrict raw input at the formatter level before the validator runs. Keep the decimal separator as '.' internally; locale-aware formatting can be layered later.
Testing Requirements
Write widget tests using flutter_test: (1) render with no prefillValue — field is empty; (2) render with prefillValue: 23.0 — field displays '23.0'; (3) simulate typing '15' — onChanged fires with 15.0; (4) simulate typing non-numeric string — onChanged fires with null; (5) verify keyboardType is numberWithOptions; (6) verify minimum rendered height is ≥48dp using tester.getSize(). Aim for 100% branch coverage of the constructor and onChanged path.
Triggering MileageCalculationService on every keystroke in the distance field could cause frame drops on lower-end Android devices if the widget rebuild chain is too broad. Jank during real-time calculation would degrade the peer-mentor experience, particularly for users with motor impairments who may type slowly and need immediate feedback.
Mitigation & Contingency
Mitigation: Keep the reimbursement calculation inside the RealtimeReimbursementDisplay widget subtree only, using a StatefulWidget with a local state variable rather than lifting state to the BLoC. This limits rebuilds to a single widget. Profile on a low-end device (Qualcomm Snapdragon 450 class) before code review.
Contingency: If profiling shows frame drops, debounce the onChanged callback by 50ms using a Timer before updating the local state, which remains imperceptible to the user while eliminating excessive rebuilds.
The optional destination field requires balancing two competing requirements: WCAG 2.2 AA demands a clear label association for screen readers, while the privacy requirement means the label must communicate optionality and privacy sensitivity without exposing the user to undue pressure to fill it in. A poorly worded label could cause screen-reader users to misunderstand the field's optional nature or feel compelled to enter private location data.
Mitigation & Contingency
Mitigation: Draft label text and hint text with input from at least one screen-reader user during the accessibility review. Use Flutter's Semantics widget to provide a separate semantic label that is more descriptive than the visual placeholder. Test with TalkBack and VoiceOver before sign-off.
Contingency: If user testing reveals confusion, replace the inline hint with a tappable information icon that opens a brief explanation of why the field is optional and how the data is used, reducing cognitive load on the field label itself.
If OrgRateConfigRepository has not yet resolved the org rate when the form loads (e.g. slow network, first launch with empty cache), the reimbursement display cannot show a meaningful value. Showing '0' or an error state could confuse mentors and undermine trust in the feature.
Mitigation & Contingency
Mitigation: Display a loading skeleton in the reimbursement display widget until the rate is available. Once loaded, animate the value in. Show a subtle 'rate unavailable' message if the fetch times out, but allow form completion and submission (rate will be fetched server-side at submission time).
Contingency: If rate unavailability is frequent due to connectivity issues, store the last successfully fetched rate in SharedPreferences as an additional fallback so the widget can render a stale-but-indicative value with a caveat label.