Add delta indicator and animation to comparison widget
epic-periodic-summaries-ui-task-002 — Enhance the PeriodComparisonWidget with animated directional delta indicators. Implement color-coded trend arrows (positive/negative/neutral), animated number transitions when data loads, and percentage change formatting. Ensure indicators are meaningful even when prior period has zero values (avoid divide-by-zero). Support both compact and expanded display modes.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Extract delta calculation into a pure function `calculateDelta(double current, double previous) -> DeltaResult` returning a sealed class/enum with the percentage and direction. This makes it trivially testable without widget overhead. For the divide-by-zero case, check `previous == 0` before dividing; return a `DeltaResult.newValue` variant. For animations, use `AnimationController` + `Tween
Check `MediaQuery.of(context).disableAnimations` and skip the animation controller if true — jump directly to end value. Use `TickerProviderStateMixin` on the parent `StatefulWidget`. Keep animation duration at 250–300ms.
Testing Requirements
Unit tests: (1) delta calculation helper returns correct percentage for all cases including zero-previous, (2) zero/zero case returns neutral indicator, (3) positive/negative/neutral states produce correct color tokens. Widget tests: (1) compact vs expanded mode renders correct child widgets, (2) accessibility setting disables animation. Golden tests for each delta state (positive, negative, neutral, new, zero/zero).
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a prior period (e.g., previous quarter's card is still cached), the digest card could appear on the home screen with outdated numbers after a new period begins, confusing users who have already seen that data.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.