Design and Implement a Reusable Comment Input-and-Feed Component in React

Goal

Build a reusable React component that provides a comment input and feed, suitable for both a video details page (slower-paced comments) and a live chat/danmaku context (high-throughput). The component should be resilient, accessible, and performant.

Requirements

1. Core interactions

• Users can type a comment and submit it to append/prepend to the list.
• Users can delete individual comments.

2. Pagination and infinite scroll

• Implement backend pagination with infinite scroll.
• Explain scroll detection (e.g., IntersectionObserver), deduplicating requests, end-of-list detection, and empty-state handling.

3. Loading and error states

• Model and display UI for: initial load, load-more, submit, and delete.
• Model and display error states for these operations.

4. Prevent duplicate submissions

• Prevent client-side duplicates via UI disabling, in-flight tracking, and debouncing.
• Use idempotency keys for submissions; discuss server-side idempotency design.

5. Optimistic UI

• Implement optimistic posting and deleting.
• Describe placeholder/tombstone items, reconciliation on success, rollback on failure, and conflict resolution.

6. Reusability and extensibility

• Make the component extensible for both a video details page and a live chat/danmaku context.
• Define component boundaries, props/interfaces, render overrides/slots.
• Discuss state management options (local state vs global store vs React Query), virtualization, throttling/backpressure, and performance under high-throughput updates.

7. Accessibility

• Include keyboard navigation, ARIA roles, and focus management.

8. Testing plan

• Provide a testing strategy covering unit, integration, and mocked network tests.

Assume a typical REST API with cursor-based pagination. If something is unspecified, make minimal explicit assumptions and state them.