Integrate fl_chart for bar chart rendering
epic-coordinator-statistics-dashboard-ui-task-004 — Wire the fl_chart adapter into the MonthlyActivityBarChart widget. Implement BarChart configuration with monthly x-axis labels, activity-count y-axis, grouped bars for activity types if filtered, touch interaction callbacks, and animated entry. Ensure the adapter exposes a clean interface so the chart widget has no direct fl_chart dependency.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Define the BarChartAdapter as a pure Dart abstract class in `lib/features/statistics/adapters/bar_chart_adapter.dart`. The concrete FlChartBarChartAdapter lives in the same directory and is the only file that imports `package:fl_chart/fl_chart.dart`. Expose a Riverpod `barChartAdapterProvider` (or inject via BLoC constructor) so tests can substitute a fake adapter. For grouped bars, order rods consistently by activity type ID to avoid color flicker across rebuilds.
Retrieve all colors via `AppColors.activityTypeColor(typeId)` design token accessor — never use Color(0x…) literals. The animation controller should be owned by the consuming widget (MonthlyActivityBarChart), not the adapter; the adapter only returns static configuration. Use `BarChartData.copyWith` for incremental updates to avoid full data reconstruction on filter changes.
Testing Requirements
Unit tests (flutter_test): (1) Adapter maps empty input to empty BarGroups without throwing. (2) Adapter maps 12 months of single-type data to 12 single-rod groups with correct rod values. (3) Adapter maps 12 months of 3-type data to 12 three-rod groups. (4) Touch callback receives correct month/type/count when onBarTouched fires.
(5) Color resolution uses design tokens — mock the token provider and assert no raw hex strings appear in rod data. Widget golden test: adapter wired to a test BarChart renders without overflow on a 375 × 300 canvas. No integration tests required at adapter level.
PeerMentorStatsList must handle rosters of 40+ mentors efficiently. A naive ListView implementation that re-renders all rows on filter change may cause frame drops on mid-range devices, degrading the experience for coordinators managing large chapters.
Mitigation & Contingency
Mitigation: Use ListView.builder with const constructors for row widgets. Profile the list with Flutter DevTools on a release build against a 60-mentor dataset before submitting for review. Implement sort in the BLoC layer, not in the widget.
Contingency: If frame drops persist, introduce pagination (load 20 mentors, scroll to load more) and add a search filter to reduce visible row count in practice.
The ActivityTypeDonutChart must render org-configured activity type labels from the org-labels system. If the terminology provider is not available or returns stale labels, chart segments will display raw key strings instead of human-readable organisation-specific names, confusing coordinators.
Mitigation & Contingency
Mitigation: Always resolve labels through the OrganizationLabelsProvider before passing data to the donut chart widget. Implement a fallback that formats the raw key as a readable string (e.g., 'peer_support' → 'Peer Support') if the provider returns null.
Contingency: If the org-labels system is unavailable, display the formatted fallback label and log a warning. Do not block chart rendering on label resolution — render with fallbacks immediately.
fl_chart widgets do not natively expose semantic labels for individual bars and donut segments. Without explicit Semantics wrappers, VoiceOver and TalkBack users will receive no meaningful chart information, failing accessibility requirements critical for Blindeforbundet and NHF deployments.
Mitigation & Contingency
Mitigation: Wrap each fl_chart widget in a Semantics widget with a descriptive label summarising the chart data. Implement the data table fallback toggle from the start, not as an afterthought. Validate with VoiceOver on iOS and TalkBack on Android during development.
Contingency: If fl_chart's rendering pipeline prevents semantic overlay from working reliably, replace chart widgets with a custom Canvas-based implementation that has full semantic control, or use a different charting library with better accessibility support.
The period filter state must be preserved when navigating away from the dashboard (e.g., drilling into a mentor's detail screen and pressing back). If the BLoC is re-created on navigation, the filter resets to default, forcing coordinators to re-select their period every time they drill down, degrading operational workflow efficiency.
Mitigation & Contingency
Mitigation: Provide the StatsBloc at a route level above the dashboard screen using a BlocProvider scoped to the statistics navigation shell, not inside the screen widget itself. Verify persistence with a widget integration test that navigates away and back.
Contingency: If route-level scoping is not achievable within the current navigation architecture, persist the last-used filter to a local session store and restore it on screen re-entry.