package radio

import (
	"bytes"
	"strconv"
	"sync"
	"time"

	"github.com/pkg/errors"
)

const MostListenedDateFormat string = "02 January 2006 at 15:04:05 MST"

// MostListenedSong holds a metadata for a most listened song.
type MostListenedSong struct {
	mutex     sync.RWMutex
	Date      time.Time `json:"date"`
	Listeners int       `json:"listeners"`
	Song      string    `json:"song"`
	changed   bool
}

func (mls *MostListenedSong) Update(song Song) {
	mls.mutex.Lock()
	defer mls.mutex.Unlock()
	if song.Artist == "" {
		return
	}
	if song.MaxListeners > mls.Listeners {
		mls.Listeners = song.MaxListeners
		mls.Date = song.StartAt
		mls.Song = song.Artist + " - " + song.Title
		mls.changed = true
	}
}

func (mls *MostListenedSong) Get() *MostListenedSong {
	mls.mutex.RLock()
	defer mls.mutex.RUnlock()

	if mls.Date.Year() == 1 {
		return nil
	}

	return &MostListenedSong{
		Date:      mls.Date,
		Listeners: mls.Listeners,
		Song:      mls.Song}
}

// Load parses given data and fill a MostListenedSong.
func (mls *MostListenedSong) Load(data []byte) (err error) {
	mls.mutex.Lock()
	defer mls.mutex.Unlock()

	lines := bytes.Split(data, []byte{'\n'})
	if len(lines) != 3 {
		return errors.New("lines count mismatch, should be 3")
	}

	var date time.Time
	if date, err = time.Parse(time.RFC3339, string(lines[0])); err != nil {
		return errors.Wrap(err, "wrong date/time format")
	}

	var listeners int
	if listeners, err = strconv.Atoi(string(lines[1])); err != nil {
		return errors.Wrap(err, "a listeners number failed to parse")
	}

	if len(lines[2]) == 0 {
		return errors.New("a song is empty")
	}

	mls.Date = date
	mls.Listeners = listeners
	mls.Song = string(lines[2])
	return nil
}

// Store returns a byte slice of a marshalled to text MostListenedSong.
func (mls *MostListenedSong) Store() []byte {
	if !mls.changed {
		return nil
	}

	buf := make([]byte, 0, 30+len(mls.Song))
	b := bytes.NewBuffer(buf)

	b.WriteString(mls.Date.Format(time.RFC3339))
	b.WriteByte('\n')
	b.WriteString(strconv.Itoa(mls.Listeners))
	b.WriteByte('\n')
	b.WriteString(mls.Song)

	return b.Bytes()
}