Composes a AWS CloudFormation template from multiple sources using deep-merge

compose-template.js

#!/usr/bin/env node

const glob = require("glob");
const yargs = require("yargs");
const { hideBin } = require("yargs/helpers");
const path = require("path");
const fs = require("fs");
const yaml = require("yaml");
const lodash = require("lodash");

const argv = yargs(hideBin(process.argv))
  .option("folder", { type: "string", alias: "f", default: ".aws/template" })
  .option("output", { type: "string", alias: "o", default: "template.yml" })
  .demandOption("folder")
  .demandOption("output")
  .parse();

const parts = [];

const tags = {
  "!Base64": "Fn::Base64",
  "!Cidr": "Fn::Cidr",
  "!FindInMap": "Fn::FindInMap",
  "!GetAtt": "Fn::GetAtt",
  "!GetAZs": "Fn::GetAZs",
  "!ImportValue": "Fn::ImportValue",
  "!Join": "Fn::Join",
  "!Select": "Fn::Select",
  "!Split": "Fn::Split",
  "!Sub": "Fn::Sub",
  "!Transform": "Fn::Transform",
  "!Ref": "Ref",
  "!Condition": "Condition",
  "!And": "Fn::And",
  "!Equals": "Fn::Equals",
  "!If": "Fn::If",
  "!Not": "Fn::Not",
  "!Or": "Fn::Or",
};

const customTags = [];

for (const key in tags) {
  if (tags.hasOwnProperty(key)) {
    const value = tags[key];
    customTags.push({
      tag: key,
      identity: () => true,
      resolve: (_, cst) => {
        return {
          [value]: yaml.parse(cst.rawValue, {
            customTags,
          }),
        };
      },
    });
  }
}

for (const filePath of glob.sync(path.join(argv.folder, "**/*.{yml,yaml}"))) {
  let fileContent = fs.readFileSync(filePath, { encoding: "utf-8" });
  let data = yaml.parse(fileContent, { customTags });
  parts.push(data);
}

if (parts.length > 0) {
  fs.writeFileSync(
    argv.output,
    yaml.stringify(lodash.merge(...parts), { customTags }),
    { encoding: "utf-8" }
  );
}