feat: Initial clean release of CHM

packages/lib/services/conflict/wordDiff.ts

@@ -0,0 +1,75 @@
+import { Diff } from 'diff';
+
+export interface WordDiffSegment {
+	text: string;
+	highlighted: boolean;
+}
+
+export interface WordDiff {
+	local: WordDiffSegment[];
+	remote: WordDiffSegment[];
+}
+
+// Prevents very large texts from blocking the UI. The limit is higher than the
+// merge limit, since a short wait is better than no word diff at all
+const diffTimeoutMs = 3000;
+
+// jsdiff only treats Latin text as words, so scripts like Cyrillic, Greek,
+// and Arabic are split character by character. CJK is kept this way on
+// purpose, since treating each character as a token gives better diffs
+const cjk = '\\p{sc=Han}\\p{sc=Hiragana}\\p{sc=Katakana}';
+const tokenRegex = new RegExp(`(?:(?![${cjk}])[\\p{L}\\p{N}_])+|[${cjk}]|\\s+|[^\\s]`, 'gu');
+
+class UnicodeWordDiff extends Diff<string, string> {
+	public tokenize(value: string) {
+		return value.match(tokenRegex) ?? [];
+	}
+}
+
+const unicodeWordDiff = new UnicodeWordDiff();
+
+const pushSegment = (side: WordDiffSegment[], text: string, highlighted: boolean) => {
+	if (text === '') return;
+	const last = side[side.length - 1];
+	if (last && last.highlighted === highlighted) {
+		last.text += text;
+	} else {
+		side.push({ text, highlighted });
+	}
+};
+
+const wholeTextSegment = (text: string): WordDiffSegment[] => {
+	return text === '' ? [] : [{ text, highlighted: true }];
+};
+
+// Splits both sides of a conflict into highlighted segments. Joining the
+// segments always gives back the original text
+export const wordDiff = (localText: string, remoteText: string): WordDiff => {
+	const local = localText ?? '';
+	const remote = remoteText ?? '';
+
+	if (local === remote) {
+		return {
+			local: local === '' ? [] : [{ text: local, highlighted: false }],
+			remote: remote === '' ? [] : [{ text: remote, highlighted: false }],
+		};
+	}
+
+	const changes = unicodeWordDiff.diff(local, remote, { timeout: diffTimeoutMs });
+	if (!changes) {
+		return { local: wholeTextSegment(local), remote: wholeTextSegment(remote) };
+	}
+
+	const result: WordDiff = { local: [], remote: [] };
+	for (const change of changes) {
+		if (change.added) {
+			pushSegment(result.remote, change.value, true);
+		} else if (change.removed) {
+			pushSegment(result.local, change.value, true);
+		} else {
+			pushSegment(result.local, change.value, false);
+			pushSegment(result.remote, change.value, false);
+		}
+	}
+	return result;
+};