package main

import (
	"bytes"
	"errors"
	"fmt"
	"math"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/mmcdole/gofeed"
)

const durationPattern = `^([0-9]+:)?([0-9]+:)?([0-9]+(\.[0-9]+)?)$`

var durationRegexp = regexp.MustCompile(durationPattern)

func main() {
	playlist, err := feed2m3u("https://feeds.soundcloud.com/users/soundcloud:users:520257816/sounds.rss")
	if err != nil {
		panic(err)
	}

	fmt.Println(playlist)
}

func feed2m3u(feedURL string) (string, error) {
	parser := gofeed.NewParser()
	feed, err := parser.ParseURL(feedURL)
	if err != nil {
		return "", err
	}

	defaultAuthor := "No Author"
	if feed.Author != nil && feed.Author.Name != "" {
		defaultAuthor = feed.Author.Name
	}

	defaultTitle := "No Title"
	if feed.Title != "" {
		defaultTitle = feed.Title
	}

	playlistBuffer := bytes.NewBuffer(nil)

	fmt.Fprintln(playlistBuffer, "#EXTM3U")

	for _, item := range feed.Items {
		duration := -1
		if item.ITunesExt != nil && item.ITunesExt.Duration != "" {
			duration, err = normalizeDuration(item.ITunesExt.Duration)
			if err != nil {
				return "", err
			}
		}

		title := defaultTitle
		if item.Title != "" {
			title = item.Title
		}

		author := defaultAuthor
		if item.Author != nil && item.Author.Name != "" {
			author = item.Author.Name
		}

		for _, enclosure := range item.Enclosures {
			if strings.HasPrefix(strings.ToLower(enclosure.Type), "audio/") {
				fmt.Fprintf(playlistBuffer, "\n#EXTINF:%d, %s - %s\n%s\n", duration, title, author, enclosure.URL)
				break
			}
		}
	}

	return playlistBuffer.String(), nil
}

func normalizeDuration(durationString string) (int, error) {
	durationString = strings.ReplaceAll(durationString, " ", "")

	ok := durationRegexp.MatchString(durationString)
	if ok {
		durationComponents := strings.Split(durationString, ":")
		var total float64 = 0
		for i, value := range durationComponents {
			intValue, err := strconv.ParseFloat(value, 64)
			if err != nil {
				return 0, err
			}
			total += intValue * math.Pow(60, float64(len(durationComponents)-i-1))
		}

		return int(total), nil
	}

	durationString = strings.ReplaceAll(durationString, "min", "m")
	durationString = strings.ReplaceAll(durationString, "sec", "s")
	if duration, err := time.ParseDuration(durationString); err == nil {
		return int(duration.Seconds()), nil
	}

	return 0, errors.New("NormalizeDuration: duration didn't match the duration pattern")
}