---
phase: 08-diff-viewer-download
plan: 01
subsystem: ui
tags: [react, diff-viewer, tanstack-query, tailwind]

requires:
  - phase: 07-config-history-ui
    provides: ConfigHistorySection timeline component with ConfigChangeEntry data
  - phase: 06-config-history-api
    provides: GET /config/{snapshot_id}/diff endpoint returning DiffResponse
provides:
  - DiffViewer component with unified diff rendering (green/red line highlighting)
  - configHistoryApi.getDiff() API client method
  - Clickable timeline entries in ConfigHistorySection
affects: [08-diff-viewer-download]

tech-stack:
  added: []
  patterns: [inline diff viewer with line-level classification]

key-files:
  created:
    - frontend/src/components/config/DiffViewer.tsx
  modified:
    - frontend/src/lib/api.ts
    - frontend/src/components/config/ConfigHistorySection.tsx

key-decisions:
  - "DiffViewer rendered inline above timeline (not modal) for context preservation"
  - "Line classification function for unified diff: +green, -red, @@blue, ---/+++ muted"

patterns-established:
  - "Inline viewer pattern: state-driven component rendered above list, closed via callback"

requirements-completed: [UI-03]

duration: 1min
completed: 2026-03-13
---

# Phase 8 Plan 1: Diff Viewer Summary

**Inline diff viewer with green/red line highlighting, wired into clickable config history timeline entries**

## Performance

- **Duration:** 1 min
- **Started:** 2026-03-13T04:19:53Z
- **Completed:** 2026-03-13T04:20:56Z
- **Tasks:** 2
- **Files modified:** 3

## Accomplishments
- DiffViewer component renders unified diffs with color-coded lines (green additions, red removals, blue hunk headers)
- API client getDiff method fetches diff data from backend endpoint
- Timeline entries in ConfigHistorySection are clickable with hover states

## Task Commits

Each task was committed atomically:

1. **Task 1: Add diff API client and create DiffViewer component** - `dda00fb` (feat)
2. **Task 2: Wire DiffViewer into ConfigHistorySection timeline entries** - `2cf426f` (feat)

## Files Created/Modified
- `frontend/src/components/config/DiffViewer.tsx` - Unified diff viewer with line-level color highlighting, loading skeleton, error state
- `frontend/src/lib/api.ts` - Added DiffResponse interface and configHistoryApi.getDiff() method
- `frontend/src/components/config/ConfigHistorySection.tsx` - Added click handlers, selectedSnapshotId state, inline DiffViewer rendering

## Decisions Made
- Rendered DiffViewer inline above the timeline rather than in a modal, preserving context
- Used a classifyLine helper function for clean line-type detection (handles +++ and --- separately from + and -)
- Loading skeleton uses randomized widths for visual variety

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- Diff viewer complete, ready for config download functionality (plan 08-02)
- All TypeScript compiles cleanly

---
*Phase: 08-diff-viewer-download*
*Completed: 2026-03-13*