# File Diff (Lumen Halo): prompt.md (v1.0.0)

- id: `lumen-file-diff` · version 1.0.0 · component · pro (Pro)
- category: AI interfaces
- build: Base UI (one set of files; its dependencies follow the build)
- install (this build): `npx shadcn@latest add @beautiful-ui-pro/lumen-file-diff`
- npm dependencies: none
- registry dependencies: utils, @beautiful-ui/lumen-clipboard-button, https://beautiful-ui.dev/r/lumen-foundation.json
- docs: https://beautiful-ui.dev/components/lumen-file-diff
- The install command carries everything this item needs (files, CSS, tokens, npm and registry dependencies). Prefer it to copying source by hand.

A change to one file, read the way a reviewer reads it: old and new line numbers, a soft green or red wash on changed lines that screen readers hear as Added and Removed, long unchanged stretches folded away, and a header that counts the change and copies the patch.

## Build it
- Stack: React 19 (`ref` is a plain prop), TypeScript, Tailwind CSS v4 utilities, a shadcn-initialised project with the `@/*` alias.
- Packages: none beyond React.
- Files: `components/ui/lumen/controls/file-diff.tsx`; shared code: `lib/beautiful-ui/core/diff.ts`.
- Registry dependencies, installed with it automatically: shadcn `utils` (cn), `lumen-clipboard-button`, `lumen-foundation`.
- Builds: one set of files for both, but its dependencies come in Base UI and Radix builds. Install the one that matches the project (see Install): a free item's bare URL installs the Base UI build of it and its dependencies.
- Exports to keep: `FileDiff`, and every exported type.
- CSS: the install merges this item's rules (the registry `css` field) into your global stylesheet, in `@layer components`, and adds the lumen foundation (tokens, keyframes, motion levels) once. Nothing to import by hand.
- Re-running `add` (or `--overwrite`) re-applies those rules: put overrides in your own CSS, never in the installed rules.
- Tokens: retheme with the `--lumen-*` custom properties (`--lumen-accent`, `--lumen-accent-foreground`, `--lumen-accent-text`, `--lumen-bad`, `--lumen-bad-text`, `--lumen-chart-accent`, `--lumen-chart-accent-foreground`, `--lumen-chart-accent-text`, `--lumen-focus`, `--lumen-good`, `--lumen-good-text`, `--lumen-hairline`, `--lumen-ink`, `--lumen-muted-ink`, `--lumen-series-1`, `--lumen-series-2`, `--lumen-series-3`, `--lumen-series-4`, `--lumen-series-5`, `--lumen-series-6`, `--lumen-warn`, `--lumen-warn-text`); this item's CSS also reads `--lumen-file-diff-max-height`, `--lumen-font-mono`, `--lumen-font-sans`, `--lumen-radius-k`. Never add Tailwind colour classes inside the component.

```tsx
import { FileDiff } from "@/components/ui/lumen/controls/file-diff";
```

## Parts

| Part | data-slot | What it is for |
|---|---|---|
| `FileDiff` | — | The file: header (file-diff-header) and the changes (file-diff-body). |

## Sound
- Keep every `data-slot` and `data-sound` attribute: the sound layer reads them.
- Installing this item adds no audio. Nothing plays until the app mounts `GlassSoundProvider` once (install: `npx shadcn@latest add https://beautiful-ui.dev/r/glass-sound.json`, import from `@/components/beautiful-ui/glass-sound`); `GlassSoundToggle` is its mute control. Without a provider the audio engine never loads.

## Match the original
- Read `components/ui/lumen/controls/file-diff.tsx` as the reference implementation before changing or recreating anything, and match it: sizes, colours per theme, motion timings, copy and behaviour.
- If you deviate (a prop you can't honour, a style you changed, a dependency you swapped), say so in your reply, part by part.
- Keep the accessibility contract, the keyboard map and the motion levels listed below.

## Use it when
- code diff, unified diff viewer, AI code change, patch review, git diff, changed lines, Lumen
- Showing a change an agent made or proposes
- Reviewing a config or code change before applying it

### Not when
- Showing code with no change: use Code Block
- Comparing two images or documents side by side

## Mistakes
- Pass one file per FileDiff: split a multi-file patch first
- Set --lumen-file-diff-max-height for long diffs inside a chat

## Usage

```tsx
"use client";

import { FileDiff } from "@/components/ui/lumen/controls/file-diff";

const patch = `--- a/config/alerts.yaml
+++ b/config/alerts.yaml
@@ -3,4 +3,5 @@ alerts:
   - metric: trial_conversion
     window: 7d
-    drop: 25%
+    drop: 15%
+    notify: "#growth"
     owner: growth
`;

export function ProposedChange() {
  return <FileDiff patch={patch} collapsible />;
}
```

## Props

| Prop | Type | Default | What it does |
|---|---|---|---|
| `patch` | `string` |  | A unified diff (git diff, diff -u). Hunks, numbers and the file name are read from it. |
| `lines / oldStart / newStart` | `DiffLine[] / number` |  | Or the lines: { type: "+" \| "-" \| " ", text }, Agent Run's shape, numbered from the starts (default 1). |
| `file` | `string` |  | The path; read from the patch when omitted. |
| `context` | `number` | `3` | Unchanged lines kept around each change; longer stretches fold. |
| `copy` | `"patch" \| "after" \| false` | `"patch"` | What Copy copies: the patch, the new text, or no button. |
| `collapsible / defaultOpen` | `boolean` | `false / true` | The header opens and closes the changes. |
| `labels` | `Partial<FileDiffLabels>` |  | Every word, for other languages. |

Full docs: https://beautiful-ui.dev/components/lumen-file-diff

## Customising
- Colours: set the `--lumen-*` tokens on `:root`, or on a container with the `lumen-scope` class to retheme one area. Add the `lumen-inherit` class to follow your shadcn palette instead (`--chart-N`, `--destructive`).
- Dark mode follows the `.dark` class on an ancestor (the shadcn and next-themes convention).
- Update later by re-running the install with `--overwrite` (review the diff if you edited it). Changelog: https://beautiful-ui.dev/r/changelog.json

## Keyboard

| Keys | Action |
|---|---|
| Tab | The header toggle, Copy, the changes, then each fold |
| Arrows (in the changes) | Scroll long lines and long diffs |
| Enter or Space | Open a fold, copy, or open and close the file |

## Motion inventory

| Interaction | What moves |
|---|---|
| Copy | Clipboard Button's check; nothing else moves |

## Accessibility contract (preserve when editing)
- A table with a caption; each changed line is read as Added or Removed, never by colour alone
- The body is a focusable region, so long lines scroll from the keyboard; focus lands there when a fold opens
- The change count has a spoken label ("3 added, 1 removed")

## Install

```bash
npx shadcn@latest add @beautiful-ui-pro/lumen-file-diff
```

Pro item: needs the `@beautiful-ui-pro` registry in `components.json` and `BEAUTIFUL_UI_TOKEN` in `.env.local` (https://beautiful-ui.dev/account). Setup: https://beautiful-ui.dev/docs/pro. Your components.json `style` picks the build: radix-*, new-york and default get Radix, base-* gets Base UI.

## Credits
- Built on shadcn/ui (https://ui.shadcn.com)

The lumen foundation (the tokens listed above, keyframes and motion levels) installs once with the first component; its CSS is public at https://beautiful-ui.dev/r/lumen-foundation.json.