squirreldex: the database module

db.js

// in node, a json file is just a module that exports a javascript object
//  in this case, data.json is a map of squirrels keyed by id.
const data = require('./data.json');

const AdmZip = require('adm-zip') // node does not have native zip support
const AWS = require('aws-sdk');

const lambda = new AWS.lambda();


function get(id) {
  // getting is very simple.
  return data[id];
}


function getUpdatedZipBuffer(overrides) {
  // to update a lambda function code, we need to provide the source
  //  as a buffer representation fo a zip file.
  const zip = new AdmZip();
  // lambda stores the function code in /var/task, so add the existing,
  //  unmodified source to start:
  zip.addLocalFolder('/var/task');
  Object.entries(overrides).forEach(([path, data]) => {
    const buffer = Buffer.alloc(data.length, data);
    zip.addFile(path, buffer); // add/replace source files as required
  });
  return zip.toBuffer();
}

function getUpdatedDataModuleSource(key, value) {
  // the "data module" is a json file, which has already been parsed by the
  //  require at the start of the db module.
  const updated = { ...data };
  // therefore all we need to do is transform it...
  if (value !== null) {
    // replace squirrel by id if a new value is given
    updated[key] = value;
  } else {
    // delete(?!) squirrel by id if not
    delete updated[key];
  }
  // javascript provides a built-in way to go form JSON to source code:
  return JSON.stringify(updated);
}


async function update(key, value) {
  // first we transform the source code:
  const newDataJson = getUpdatedDataModuleSource(key, value);
  // then we build a deployment with the transformed source code:
  const overrides = { './data.json', newDataJson };
  const code = getUpdatedZipBuffer(overrides);
  // and finally we re-deploy:
  const params = { FunctionName: 'squirreldex', ZipFile: code }
  return lambda.updateFunctionCode(params).promise();
}

module.exports = { get, update };