From 10ce0d23651fc2c96fd0d276147cd48105e21b84 Mon Sep 17 00:00:00 2001
From: Timothy Jaeryang Baek <tim@openwebui.com>
Date: Thu, 15 Oct 2026 15:23:52 +0400
Subject: [PATCH] refac

---
 src/lib/components/common/diffEditor.ts       | 42 +++++++++++++++++++
 .../components/common/diffEditorAlignment.ts  | 29 ++++---------
 2 files changed, 50 insertions(+), 21 deletions(-)

diff --git a/src/lib/components/common/diffEditor.ts b/src/lib/components/common/diffEditor.ts
index c1519c6b73..877e3b4584 100644
--- a/src/lib/components/common/diffEditor.ts
+++ b/src/lib/components/common/diffEditor.ts
@@ -6,6 +6,48 @@ export const diffEditorConfig: DiffConfig = { timeout: 100 };
 
 export type MergeDirection = 'to-working' | 'to-proposal';
 
+// Match rows by the text preserved inside a chunk, not their ordinal position.
+export function changedLinePairs(a: Text, b: Text, chunk: Chunk): [number, number][] {
+	const candidates = new Map<number, Map<number, { a: number; b: number; weight: number }>>();
+	let fromA = chunk.fromA;
+	let fromB = chunk.fromB;
+	for (let index = 0; index <= chunk.changes.length; index++) {
+		const change = chunk.changes[index];
+		const endA = change ? chunk.fromA + change.fromA : Math.min(chunk.toA, a.length);
+		const endB = change ? chunk.fromB + change.fromB : Math.min(chunk.toB, b.length);
+		while (fromA < endA && fromB < endB) {
+			const lineA = a.lineAt(fromA),
+				lineB = b.lineAt(fromB);
+			const length = Math.min(endA - fromA, endB - fromB, lineA.to - fromA, lineB.to - fromB);
+			const weight = a.sliceString(fromA, fromA + length).replace(/\s/g, '').length;
+			if (weight) {
+				let row = candidates.get(lineA.from);
+				if (!row) candidates.set(lineA.from, (row = new Map()));
+				const pair = row.get(lineB.from) ?? { a: lineA.from, b: lineB.from, weight: 0 };
+				pair.weight += weight;
+				row.set(lineB.from, pair);
+			}
+			fromA += length || 1;
+			fromB += length || 1;
+		}
+		if (change) {
+			fromA = chunk.fromA + change.toA;
+			fromB = chunk.fromB + change.toB;
+		}
+	}
+	const bestA = new Map<number, { a: number; b: number; weight: number }>();
+	const bestB = new Map<number, { a: number; b: number; weight: number }>();
+	for (const row of candidates.values()) {
+		for (const pair of row.values()) {
+			if (pair.weight > (bestA.get(pair.a)?.weight ?? 0)) bestA.set(pair.a, pair);
+			if (pair.weight > (bestB.get(pair.b)?.weight ?? 0)) bestB.set(pair.b, pair);
+		}
+	}
+	return [...bestA.values()]
+		.filter((pair) => bestB.get(pair.b) === pair)
+		.map((pair) => [pair.a, pair.b]);
+}
+
 export function changedLineCounts(a: Text, b: Text, chunks: readonly Chunk[]) {
 	const count = (doc: Text, side: 'A' | 'B') => {
 		let total = 0;
diff --git a/src/lib/components/common/diffEditorAlignment.ts b/src/lib/components/common/diffEditorAlignment.ts
index 129259ef6f..0e4d2f1e9a 100644
--- a/src/lib/components/common/diffEditorAlignment.ts
+++ b/src/lib/components/common/diffEditorAlignment.ts
@@ -7,16 +7,19 @@ import {
 	type DecorationSet
 } from '@codemirror/view';
 import type { Chunk } from '@codemirror/merge';
+import { changedLinePairs } from './diffEditor';
 
 export function pairedLinePosition(a: Text, b: Text, chunks: readonly Chunk[], position: number) {
 	let offset = 0;
 	for (const chunk of chunks) {
 		if (position < chunk.fromA) break;
 		if (position < chunk.toA) {
-			const row = a.lineAt(position).number - a.lineAt(chunk.fromA).number;
-			const start = b.lineAt(Math.min(chunk.fromB, b.length)).number;
-			const end = b.lineAt(Math.min(Math.max(chunk.fromB, chunk.toB - 1), b.length)).number;
-			return b.line(Math.min(start + row, end)).from;
+			const pairs = changedLinePairs(a, b, chunk);
+			const line = a.lineAt(position).from;
+			return (
+				(pairs.find(([from]) => from >= line) ?? pairs.at(-1))?.[1] ??
+				Math.min(chunk.fromB, b.length)
+			);
 		}
 		offset = chunk.toB - chunk.toA;
 	}
@@ -128,23 +131,7 @@ export function alignChangedLines(a: EditorView, b: EditorView, chunks: readonly
 			align(posA, posB);
 		}
 		if (!chunk) break;
-		if (chunk.fromA < chunk.toA && chunk.fromB < chunk.toB) {
-			const lineA = a.state.doc.lineAt(chunk.fromA).number,
-				lineB = b.state.doc.lineAt(chunk.fromB).number;
-			let row = Math.max(
-				0,
-				a.state.doc.lineAt(a.viewport.from).number - lineA,
-				b.state.doc.lineAt(b.viewport.from).number - lineB
-			);
-			while (lineA + row <= a.state.doc.lines && lineB + row <= b.state.doc.lines) {
-				const posA = a.state.doc.line(lineA + row).from,
-					posB = b.state.doc.line(lineB + row).from;
-				if (posA >= chunk.toA || posB >= chunk.toB || posA > a.viewport.to || posB > b.viewport.to)
-					break;
-				align(posA, posB);
-				row++;
-			}
-		}
+		for (const [posA, posB] of changedLinePairs(a.state.doc, b.state.doc, chunk)) align(posA, posB);
 		fromA = chunk.toA;
 		fromB = chunk.toB;
 	}