.master.check.js

const fs = require("fs");
const { exec } = require("child_process");

// this script aims to ensure that the master branch is never
// merged into another branch and thus will never end up in
// production

// installation:
// 1. yarn add -D husky
// 2. place this file in the root of the repository
// 3. add the following to package.json
// 4. create a .master file and commit it directly on the master branch
//
// ```
// "husky": {
//   "hooks": {
//     "pre-commit": "node .master.check.js",
//     "pre-push": "node .master.check.js",
//     "post-merge": "node .master.check.js"
//   }
// }
// ```

exec("git rev-parse --abbrev-ref HEAD", (execErr, stdout) => {
  if (execErr) {
    // something went wrong executing the git command
    console.error(`this script shouldn't be run here`);
    process.exit(2);
  }

  const branch = stdout.trim();
  fs.access(".master", fs.constants.F_OK, accessErr => {
    if (accessErr) {
      // .master file does not exists
      if (branch === "master") {
        console.warn(".master file does not exist");
        console.warn("this is the master branch, so it should");
        console.log("creating");

        fs.writeFile(".master", "", () => {
          process.exit(3);
        });
      } else {
        console.info(".master file does not exist on this branch");
        console.info("all good");

        process.exit(0);
      }
    } else {
      console.log(".master file exists");
      if (branch !== "master") {
        console.error(`this isn't the master branch so that's a problem`);

        process.exit(1);
      } else {
        console.log(`branch is master, so that's fine`);

        process.exit(0);
      }
    }
  });
});