Implement Period Comparison Widget base structure
epic-periodic-summaries-ui-task-001 — Build the reusable PeriodComparisonWidget Flutter widget that displays side-by-side or stacked period data with directional delta indicators (up/down arrows with percentage change). Widget should accept two PeriodicSummary objects and render metric tiles showing current vs previous period values with color-coded deltas. Must support offline rendering from cached data.
Acceptance Criteria
Technical Requirements
Implementation Notes
Define a `PeriodicSummary` model class (or confirm it exists) with typed fields for sessions, hours, and contacts counts before building the widget. Use a `PeriodComparisonLayout` enum (`sideBySide`, `stacked`) to control layout. Internal `MetricTile` widget should be a private stateless widget within the same file to keep the API surface minimal. Use `Flexible` / `Expanded` inside Row/Column layouts to handle varying screen widths.
For offline support, the widget is purely presentational — it does not fetch data; the parent BLoC/provider supplies the data objects. Prefer `const` constructors everywhere to minimize rebuild cost. Apply design tokens via the project's token system (e.g., `AppColors.textPrimary`, `AppSpacing.md`) — never inline hex.
Testing Requirements
Unit tests with flutter_test covering: (1) widget renders with two valid PeriodicSummary objects, (2) widget renders with only current period (no previous), (3) both layout modes (side-by-side, stacked) produce correct widget trees. Golden tests for visual regression. Accessibility test asserting Semantics nodes exist for each metric tile. No integration tests required at this stage.
If the cached summary is from a prior period (e.g., previous quarter's card is still cached), the digest card could appear on the home screen with outdated numbers after a new period begins, confusing users who have already seen that data.
Mitigation & Contingency
Mitigation: In the SummaryCacheRepository, store the period_start and period_end alongside cached data. In the PeriodicSummaryCard BLoC, compare the cached record's period against the current date using PeriodCalculatorService. Only render the card if the cached summary belongs to the active period.
Contingency: If stale cards appear in production, push a hotfix that adds the period validity check to the BLoC and clears all cached summaries older than the current period boundary via a forced cache flush on next app launch.
Using colour alone to distinguish underactive from overloaded mentors in the coordinator view would fail WCAG 1.4.1 (use of colour). This is especially critical for organisations serving users with colour vision deficiency.
Mitigation & Contingency
Mitigation: Always pair colour indicators with a text label or icon (e.g., a downward arrow + 'Underactive' text alongside the amber colour). Use the contrast-safe-color-palette design tokens throughout. Run the contrast-ratio-validator on all new colour combinations in CI.
Contingency: If an accessibility audit flags colour-only indicators post-launch, introduce icon-based indicators as a patch release and update the design token definitions to enforce the paired-indicator pattern going forward.
Inserting a new card into the role-based home screen requires changes to shared home screen widget composition, which may conflict with parallel feature branches also modifying the home screen layout, causing merge conflicts and integration delays.
Mitigation & Contingency
Mitigation: Implement the PeriodicSummaryCard as a fully self-contained widget that the home screen conditionally renders based on a BLoC state flag. Minimise changes to the home screen itself to a single conditional insertion point, reducing the surface area for merge conflicts.
Contingency: If integration conflicts block the PR, isolate the card behind the organisation-scoped feature flag so it can be toggled independently and merged without affecting other home screen changes.