Post-processing script for 'serverless-manifest-plugin'. Parses manifest output and populates .env file with deployed AWS resource values. Based on: https://github.com/theburningmonk/appsyncmasterclass-backend/blob/873a6bf144e44725c389b198abec5245559fe9bf/processManifest.js

processManifest.js

const dotenv = require("dotenv");
const fs = require("fs").promises;
const path = require("path");

module.exports = async function processManifest(manifestData) {
  const stageName = Object.keys(manifestData)[0];
  const { outputs } = manifestData[stageName];
  const envArray = outputs
    .map((obj) => Object.values(obj))
    .map((arr) => [camelToUpperSnakeCase(arr[0]), arr[1]]);
  const envObject = Object.fromEntries(envArray);

  const dotEnvFile = path.resolve(".env");
  await updateDotEnv(dotEnvFile, envObject);
};

/* Utils, typically this would be a package includes from NPM */
async function updateDotEnv(filePath, env) {
  // Merge with existing values
  try {
    const existing = dotenv.parse(await fs.readFile(filePath, "utf-8"));
    env = { ...existing, ...env };
  } catch (err) {
    if (err.code !== "ENOENT") {
      throw err;
    }
  }

  const contents = Object.keys(env)
    .map((key) => format(key, env[key]))
    .join("\n");
  await fs.writeFile(filePath, contents);

  return env;
}

function escapeNewlines(str) {
  return str.replace(/\n/g, "\\n");
}

function format(key, value) {
  return `${key}=${escapeNewlines(value)}`;
}

function camelToUpperSnakeCase(str) {
  return [...str].reduce((previous, current) =>
    current === current.toUpperCase()
      ? (previous += "_" + current)
      : (previous += current.toUpperCase())
  );
}