/**
* Unified diff generation for change preview.
*
* Produces diffs in unified format (like `git diff`) for human-readable
* change visualization before applying modifications.
*/
import { createTwoFilesPatch } from 'diff';
// ─────────────────────────────────────────────────────────────
// Diff Generation
// ─────────────────────────────────────────────────────────────
/**
* Generate a unified diff between two strings.
*
* Produces standard unified diff format with 3 lines of context:
* - Lines starting with `-` are removed
* - Lines starting with `+` are added
* - Lines starting with ` ` are unchanged context
*
* @param oldContent - Original content
* @param newContent - Modified content
* @param filename - Filename for diff header (default: "file")
* @returns Unified diff string, or "(no changes)" if identical
*
* @example
* generateDiff("hello\nworld", "hello\nuniverse", "greeting.txt")
* // --- a/greeting.txt
* // +++ b/greeting.txt
* // @@ -1,2 +1,2 @@
* // hello
* // -world
* // +universe
*/
export function generateDiff(oldContent: string, newContent: string, filename = 'file'): string {
if (oldContent === newContent) {
return '(no changes)';
}
const patch = createTwoFilesPatch(
`a/${filename}`,
`b/${filename}`,
oldContent,
newContent,
'',
'',
{ context: 3 },
);
return patch.trim();
}
// ─────────────────────────────────────────────────────────────
// Diff Analysis
// ─────────────────────────────────────────────────────────────
/**
* Count lines added and removed in a diff.
*
* @param diff - Unified diff string
* @returns Count of added and removed lines
*
* @example
* const diff = generateDiff("a\nb", "a\nc\nd");
* countDiffLines(diff)
* // { added: 2, removed: 1 }
*/
export function countDiffLines(diff: string): { added: number; removed: number } {
const lines = diff.split('\n');
let added = 0;
let removed = 0;
for (const line of lines) {
if (line.startsWith('+') && !line.startsWith('+++')) added++;
if (line.startsWith('-') && !line.startsWith('---')) removed++;
}
return { added, removed };
}
