const { from, Observable, empty, bindNodeCallback } = require("rxjs")
const { mergeMap, filter, expand, map, reduce } = require("rxjs/operators")
const fs = require("fs")
const path = require("path")

const readFile = bindNodeCallback(fs.readFile)

const TRACK_PATH = `C:/Users/Linus/Downloads/Songs`

const ls = dir => from(fs.readdirSync(dir)).pipe(
    mergeMap(name => new Observable(subscriber => {
        const fullname = path.join(dir, name)
        fs.stat(fullname, (e, st) => {
            if (e) {
                return subscriber.error(e)
            }
            subscriber.next({ name: fullname, stats: st })
            subscriber.complete()
        })
    }))
)

const HEADER_SEPARATOR = Buffer.from([ 0x0D, 0x0A, 0x0D, 0x0A ])
const SEPARATOR = Buffer.from([ 0x3B, 0x0D, 0x0A ])
const FIELD_SEPARATOR = 0x3A
const HASH_POUND = 0x23

const readSMinfo = filename => readFile(filename).pipe(
    mergeMap(buffer => new Observable(subscriber => {
        let offset = buffer.indexOf(HASH_POUND) // skip utf-8 bom if it exists
        const headerStop = buffer.indexOf(HEADER_SEPARATOR)
        let index = buffer.indexOf(SEPARATOR, offset)
        while (index !== -1 && index < headerStop) {
            const field = buffer.slice(offset + 1, index)
            const colonIndex = field.indexOf(FIELD_SEPARATOR)
            subscriber.next([
                field.toString('utf8', 0, colonIndex),
                field.toString('utf8', colonIndex + 1)
            ])
            offset = index + 3
            index = buffer.indexOf(SEPARATOR, offset)
        }
        subscriber.complete()
    })),
    reduce((obj, [key, value]) => {
        obj[key] = value
        return obj
    }, {}),
    map(info => {
        let title = info.TITLE;
        if (title === undefined) {
            return null;
        }
        if (info.SUBTITLE !== undefined && info.SUBTITLE !== '') {
            title += " " + info.SUBTITLE
        }
        if (info.ARTIST !== undefined && info.ARTIST !== '') {
            title += " - " + info.ARTIST
        }
        return title
    }),
    filter(title => title !== null)
)

ls(TRACK_PATH).pipe(
    expand(f => f.stats.isDirectory() ? ls(f.name) : empty()),
    filter(f => path.extname(f.name) === ".sm"),
    map(f => f.name),
    mergeMap(readSMinfo)
)
.subscribe(console.log)