watch a group of files and, on change, touch a different file

watch-and-touch.js

// Example usage:
//  node watch-and-touch 'src/**/*.post.css' src/styles-index.post.css
//
// Example will `touch` src/styles-index.post.css if any other css file
// under src changes. Potential usecase: webpack hot module reloading is
// working for your primary postcss file, but does not work for other
// postcss files imported from the main file.
//
// See: https://github.com/postcss/postcss-loader/issues/122
// See: https://github.com/postcss/postcss-import/issues/233

var chokidar = require('chokidar'); // "^1.6.1"
var Rx = require('rxjs'); // "5.0.0-rc.2"

const exec = require('child_process').exec;

var usage = 'node watch-and-touch file-glob-to-watch file-to-touch';
var example = "node watch-and-touch 'src/**/*.post.css' src/styles-index.post.css";

var watchPath = process.argv[2];
var touchPath = process.argv[3];

if (!(watchPath && touchPath)) {
    console.error('Missing arguments');
    console.log(`usage:   ${usage}`);
    console.log(`example: ${example}`);
    process.exit(1);
}

var eventsOnWatchPath = new Rx.Subject();

// push relevant file system events to eventsOnWatchPath
chokidar.watch(watchPath, {
    ignored: /[\/\\]\./,
    persistent: true
}).on('all', (event, path) => eventsOnWatchPath.next({ event, path }));


function touch () {
    exec(`touch ${touchPath}`, err => {
        if (err) {
            console.error(err);
        } else {
            console.log(`>>> touched ${touchPath}`);
        }
    });
}

eventsOnWatchPath
    // don't recurse if touchPath is matched by watchPath
    .filter(e => e.path !== touchPath)
    // chokidar begins by emitting all files matching watchPath, skip that
    .skipUntil(Rx.Observable.timer(100))
    .do(e => console.log(`${e.event}: ${e.path}`))
    .sampleTime(500)
    .subscribe(touch);

console.log(`>> Watching ${watchPath}. Will touch ${touchPath} on changes.`);