Receipt Capture Widget — thumbnail preview and removal
epic-travel-expense-registration-ui-task-004 — Add a receipt thumbnail preview strip beneath the capture button so users can inspect the captured image before submission. Provide a remove/replace affordance with a confirmation prompt. Ensure the thumbnail is accessible with a descriptive label and that the remove action announces its result to screen readers via a live region.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
Keep thumbnail state in ExpenseFormBloc (store ReceiptAttachment with localPath and uploadedUrl). The thumbnail widget reads localPath from state and uses Image.file() for display — no extra network call. Implement ReceiptFullScreenModal as a Hero-animated route wrapping InteractiveViewer(child: Image.file(...)). For the confirmation dialog, use showDialog() with a standard AlertDialog; dispatch ReceiptRemoved to the BLoC only if the user confirms.
For the live region on removal, use a dedicated Semantics(liveRegion: true) widget whose label key switches between '' and 'Receipt removed' — toggling the key forces re-announcement. Clean up localPath File reference in the BLoC's close() method.
Testing Requirements
Widget tests: verify thumbnail visible after ReceiptAttached state; tap remove → assert dialog shown; confirm → assert thumbnail hidden and live-region label updated; cancel → assert thumbnail still visible. Test full-screen modal opens on thumbnail tap. Test replace flow: tap capture area with existing receipt → new receipt replaces old without confirmation. Accessibility: SemanticsController.find() for thumbnail label and remove button label.
Memory test: pump and dispose widget, assert no pending image file handles remain.
The image_picker Flutter plugin requires platform-specific permissions (NSPhotoLibraryUsageDescription, camera permission) and behaves differently across iOS and Android versions. Permission denial or plugin misconfiguration can silently prevent receipt attachment.
Mitigation & Contingency
Mitigation: Configure all required permission strings in Info.plist and AndroidManifest.xml during initial plugin setup. Use the permission_handler package to check and request permissions before launching the picker, with clear user-facing explanations. Test on both platforms across at least two OS versions.
Contingency: If image_picker proves unreliable on a specific platform version, fall back to file_picker as an alternative that uses the OS document picker interface, which requires fewer permissions on some Android versions.
The expense form BLoC manages interconnected state across expense type selection, field visibility, receipt requirement, threshold evaluation, and submission flow. Incorrect state transitions can cause UI inconsistencies such as required receipt indicator not updating after amount change, or form appearing valid when mutual exclusion is violated.
Mitigation & Contingency
Mitigation: Model BLoC states as sealed classes with exhaustive pattern matching. Write state transition unit tests covering every combination of: type selection change, amount field change above/below threshold, receipt attachment/removal, and offline mode toggle. Use bloc_test for comprehensive state sequence assertions.
Contingency: If BLoC complexity becomes unmanageable, split into two BLoCs — one for type selection/exclusion state and one for field values/submission — coordinating via a parent provider, accepting the small overhead of inter-BLoC communication.
The expense type selector must enforce mutual exclusion visually by disabling options and showing conflict tooltips, while remaining fully accessible to screen reader users who cannot perceive visual disable states. Incorrect semantics labelling will fail WCAG 2.2 AA requirements critical for Blindeforbundet and HLF users.
Mitigation & Contingency
Mitigation: Use Flutter Semantics widgets to explicitly set disabled state and provide conflict explanations as semanticLabel strings on disabled options. Run accessibility audits with TalkBack and VoiceOver during widget development, not post-completion. Reference the project's accessibility test harness for required test coverage.
Contingency: If custom widget accessibility is difficult to certify, implement the selector as a standard Flutter Radio/Checkbox group with built-in accessibility semantics and an explanatory Text widget below each conflicting option, sacrificing visual elegance for guaranteed WCAG compliance.