kdnk_obsidian-automatic-linker/src/update-editor.ts

import { ChangeSpec } from "@codemirror/state";
import { Editor } from "obsidian";
import DiffMatchPatch from "diff-match-patch";

function endOfDocument(doc: string) {
	const lines = doc.split("\n");
	return { line: lines.length - 1, ch: lines[lines.length - 1].length };
}

export function updateEditor(
	oldText: string,
	newText: string,
	editor: Editor,
): DiffMatchPatch.Diff[] {
	const dmp = new DiffMatchPatch.diff_match_patch();
	const changes = dmp.diff_main(oldText, newText);
	let curText = "";
	changes.forEach((change) => {
		const [type, value] = change;

		if (type == DiffMatchPatch.DIFF_INSERT) {
			// use codemirror dispatch in order to bypass the filter on transactions that causes editor.replaceRange not to not work in Live Preview
			editor?.cm?.dispatch({
				changes: [
					{
						from: editor.posToOffset(endOfDocument(curText)),
						insert: value,
					} as ChangeSpec,
				],
				filter: false,
			});
			curText += value;
		} else if (type == DiffMatchPatch.DIFF_DELETE) {
			const start = endOfDocument(curText);
			let tempText = curText;
			tempText += value;
			const end = endOfDocument(tempText);

			// use codemirror dispatch in order to bypass the filter on transactions that causes editor.replaceRange not to not work in Live Preview
			editor?.cm?.dispatch({
				changes: [
					{
						from: editor.posToOffset(start),
						to: editor.posToOffset(end),
						insert: "",
					} as ChangeSpec,
				],
				filter: false,
			});
		} else {
			curText += value;
		}
	});

	return changes;
}