setup.js

"use strict";

const fs = require("fs");
const path = require("path");
const root = process.cwd();
const node_modulesFolder = path.resolve(root, "node_modules");
const webpackDependencyFolder = path.resolve(root, "node_modules/webpack");

function setup() {
	return checkSymlinkExistsAsync()
		.then(hasSymlink => {
			if (!hasSymlink) {
				return ensureYarnInstalledAsync().then(() => {
					return runSetupAsync().then(() => {
						return checkSymlinkExistsAsync();
					});
				});
			}
		})
		.then(message => {
			process.exitCode = 0;
		})
		.catch(e => {
			console.error(e);
			process.exitCode = 1;
		});
}

function runSetupAsync() {
	return exec("yarn", ["install"], "Install dependencies")
		.then(() => exec("yarn", ["link"], "Create webpack symlink"))
		.then(() => exec("yarn", ["link", "webpack"], "Link webpack into itself"));
}

function checkSymlinkExistsAsync() {
	return new Promise((resolve, reject) => {
		if (
			fs.existsSync(node_modulesFolder) &&
			fs.existsSync(webpackDependencyFolder) &&
			fs.lstatSync(webpackDependencyFolder).isSymbolicLink()
		) {
			resolve(true);
		} else {
			resolve(false);
		}
	});
}

function ensureYarnInstalledAsync() {
	const semverPattern = /^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(-(0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(\.(0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*)?(\+[0-9a-zA-Z-]+(\.[0-9a-zA-Z-]+)*)?$/;
	return execGetOutput("yarn", ["-v"], "Check yarn version")
		.then(
			stdout => semverPattern.test(stdout),
			() => false
		)
		.then(hasYarn => hasYarn || installYarnAsync());
}

function installYarnAsync() {
	return exec("npm", ["install", "-g", "yarn"], "Install yarn");
}

function exec(command, args, description) {
	console.log(`Setup: ${description}`);
	return new Promise((resolve, reject) => {
		let cp = require("child_process").spawn(command, args, {
			cwd: root,
			stdio: "inherit",
			shell: true
		});
		cp.on("error", error => {
			reject(new Error(`${description} failed with ${error}`));
		});
		cp.on("exit", exitCode => {
			if (exitCode) {
				reject(`${description} failed with exitcode ${exitCode}`);
			} else {
				resolve();
			}
		});
	});
}

function execGetOutput(command, args, description) {
	console.log(`Setup: ${description}`);
	return new Promise((resolve, reject) => {
		let cp = require("child_process").spawn(command, args, {
			cwd: root,
			stdio: [process.stdin, "pipe", process.stderr],
			shell: true
		});
		cp.on("error", error => {
			reject(new Error(`${description} failed with ${error}`));
		});
		cp.on("exit", exitCode => {
			if (exitCode) {
				reject(`${description} failed with exitcode ${exitCode}`);
			} else {
				resolve(
					Buffer.concat(buffers)
						.toString("utf-8")
						.trim()
				);
			}
		});
		const buffers = [];
		cp.stdout.on("data", data => buffers.push(data));
	});
}

setup();