A function for expo-plugin that adds new lines to build gradle. Can be used to add lines to other files

addToBuildGradle.ts

const addToBuildGradle = (
  newLine: string,
  anchor: RegExp | string,
  offset: number,
  buildGradle: string,
) => {
  const lines = buildGradle.split('\n');
  const lineIndex = lines.findIndex((line) => line.match(anchor));
  // add after given line
  lines.splice(lineIndex + offset, 0, newLine);
  return lines.join('\n');
};

Source https://github.com/hyochan/react-native-iap/blob/b7aa8fa6d5c303bfcdae3cd75b1299280b211d9d/plugin/src/withIAP.ts#L36-L47