backup paths exercise (FRP version)

getbackuppathsRx.js

#!/usr/bin/env node

const fs = require('fs')
const path = require('path')
const readline = require('readline')

const R = require('ramda')
const Bacon = require('baconjs')
const Promise = require('bluebird')

const readdirAsync = Promise.promisify(fs.readdir)
const statAsync = Promise.promisify(fs.stat)

function readFirstLineAsync(filepath) {
    return new Promise((resolve, reject) => {
        const readStream = fs.createReadStream(filepath, 'utf8')
        readStream.on('error', reject)
        const rl = readline.createInterface({input: readStream})
        rl.on('error', reject)
        rl.on('line', line => {
            readStream.close()
            resolve(line)
        })
    })
}

function getBackupPathsRx(dir, parentpolicy='branch') {
    return Bacon.fromPromise(Promise.resolve(
        parentpolicy == 'branch' ? readFirstLineAsync(path.join(dir, '.backuppolicy')) : 'leaf'))
    .mapError('leaf')
    .map(R.pipe(
        val => val.trim(),
        policy => ['leaf', 'branch', 'ignore'].includes(policy) ? policy : 'leaf'
    ))
    .flatMap(policy =>
        Bacon.fromPromise(Promise.resolve(
            policy == 'ignore' ? [] : readdirAsync(dir)))
        .flatMap(basenames => {
            const fullpaths = basenames
                .map(R.pipe(
                    base => ({dir, base}),
                    path.format,
                    path.normalize
                ))
            return Bacon.fromArray(fullpaths)
        })
        .flatMap(fullpath => {
            const withStatsP = statAsync(fullpath)
                .then(stats => ({fullpath, stats}))
            return Bacon.fromPromise(withStatsP)
        })
        .flatMap(({fullpath, stats}) =>
            stats.isFile() ? Bacon.once(fullpath) :
            stats.isDirectory() ? getBackupPathsRx(fullpath, policy) :
            Bacon.never()
        )
    )
}

const runningAsMain = require.main == module && !module.parent
if (runningAsMain) {
    if (process.argv.length < 3)
        return console.error('no dirpath given')
    const [,, dir] = process.argv
    getBackupPathsRx(dir)
        .onValue(console.log)
} else {
    Object.assign(module.exports, {
        getBackupPathsRx
    })
}