index.ts

import { TextOperation } from 'ot';
import { stringDiff } from './lcs';

const MAX_DIFF_SIZE = 10000;

export function findDiff(
  originalText: string,
  modifiedText: string,
  pretty: boolean
) {
  return stringDiff(originalText, modifiedText, pretty);
}

export function getTextOperation(originalText: string, modifiedText: string) {
  const ot = new TextOperation();

  if (Math.max(originalText.length, modifiedText.length) > MAX_DIFF_SIZE) {
    ot.delete(originalText.length);
    ot.insert(modifiedText);

    // eslint-disable-next-line
    console.warn(
      'Not optimizing edits, file is larger than ' + MAX_DIFF_SIZE + 'b'
    );

    return ot;
  }

  const diffs = findDiff(originalText, modifiedText, false);

  let lastPos = 0;

  diffs.forEach(change => {
    const start = change.originalStart;
    const end = change.originalStart + change.originalLength;

    if (start - lastPos !== 0) {
      ot.retain(start - lastPos);
    }
    lastPos = end;

    const oldText = originalText.substr(start, change.originalLength);
    const newText = modifiedText.substr(
      change.modifiedStart,
      change.modifiedLength
    );

    if (oldText !== newText) {
      ot.insert(newText);
      ot.delete(change.originalLength);
    }
  });

  ot.retain(originalText.length - ot.baseLength);
  return ot;
}