package download

import (
	"context"
	"errors"
	"github.com/grafov/m3u8"
	"github.com/hashicorp/golang-lru/v2/expirable"
	"github.com/rs/zerolog/log"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync/atomic"
	"time"
)

type HLSOptions struct {
	Timeout     time.Duration
	MaxAttempts int
}

type HLS struct {
	ctx      context.Context
	ctxClose context.CancelFunc
	exit     chan any

	options HLSOptions
	client  *http.Client
	request *http.Request

	retryAttempts atomic.Uint32
}

func NewHLS(r func() (*http.Request, error), opts HLSOptions) (*HLS, error) {
	if r == nil {
		return nil, errors.New("illegal state: empty requester")
	}

	var (
		d = HLS{
			options: opts,
			client: &http.Client{
				Transport: func() *http.Transport {
					transport := http.DefaultTransport.(*http.Transport)
					transport.Proxy = http.ProxyFromEnvironment
					return transport
				}(),
				Timeout: opts.Timeout,
			},
		}
		err error
	)

	if d.request, err = r(); err != nil {
		return nil, err
	}

	d.ctx, d.ctxClose = context.WithCancel(context.Background())
	return &d, nil
}

func (d *HLS) Close() error {
	log.Info().Msg("request to close HLS recorder")

	if d.ctxClose != nil {
		d.ctxClose()
	}

	d.exit <- 0
	return nil
}

func (d *HLS) Start() chan []byte {
	d.exit = make(chan any)

	var (
		c         = make(chan []byte)
		medialist *m3u8.MediaPlaylist
		segments  = expirable.NewLRU[uint64, *m3u8.MediaSegment](64, nil, time.Minute)
		err       error
	)

	go func() {
		defer close(c)

		for {
			select {
			case <-d.exit:
				c <- nil
				return
			default:
				if medialist, err = d.getMediaList(); err != nil {
					log.Debug().
						Err(err).
						Msg("could not retrieve m3u8 playlist")

					c <- nil
					return
				}

				if medialist.Closed {
					c <- nil
					return
				}

				duration := time.NewTicker(time.Duration(medialist.TargetDuration) * time.Second)

				for _, seq := range medialist.Segments {
					if seq == nil {
						continue
					}

					if _, ok := segments.Get(seq.SeqId); ok {
						continue
					}

					segments.Add(seq.SeqId, seq)

					var (
						uri      = seq.URI
						request  *http.Request
						response *http.Response
						buff     []byte
					)

					// pre-handle relative segment URIs
					if !strings.HasPrefix(uri, "http") {
						if s, err := d.request.URL.Parse(uri); err != nil {
							log.Debug().Err(err).Msg("could not build segment abs segment URI")
							c <- nil
							return
						} else {
							if uri, err = url.QueryUnescape(s.String()); err != nil {
								log.Debug().Err(err).Msg("could not build segment abs segment URI")
								c <- nil
								return
							}
						}
					}

					request = d.request.Clone(d.ctx)
					request.Method = http.MethodGet

					if request.URL, err = request.URL.Parse(uri); err != nil {
						log.Debug().Err(err).Msg("could not parse segment URI")
						c <- nil
						return
					}

					if response, err = d.client.Do(request); err != nil {
						log.Debug().Err(err).Msg("could not retrieve segment data")
						c <- nil
						return
					}

					if buff, err = io.ReadAll(response.Body); err != nil {
						log.Debug().Err(err).Msg("could not read segment data")
						c <- nil
						return
					}

					_ = response.Body.Close()
					c <- buff
				}

				<-duration.C
			}
		}
	}()

	return c
}

func (d *HLS) requestMediaList(request *http.Request) (*http.Response, error) {
	var (
		response *http.Response
		err      error
	)

	response, err = d.client.Do(request)
	if err != nil && errors.Is(err, http.ErrHandlerTimeout) {
		if d.retryAttempts.Load() == uint32(d.options.MaxAttempts) {
			return nil, err
		}

		select {
		case <-time.After(time.Second):
		}

		if d.options.MaxAttempts != -1 {
			d.retryAttempts.Add(1)
		}

		return d.requestMediaList(request)
	}

	if err != nil {
		return nil, err
	}

	d.retryAttempts.Store(0)
	return response, nil
}

func (d *HLS) getMediaList() (*m3u8.MediaPlaylist, error) {
	var (
		request  *http.Request
		response *http.Response

		playlist m3u8.Playlist
		t        m3u8.ListType
		err      error
	)

	request = d.request.Clone(d.ctx)
	if response, err = d.requestMediaList(request); err != nil {
		return nil, err
	}

	if playlist, t, err = m3u8.DecodeFrom(response.Body, false); err != nil {
		return nil, err
	}

	if m3u8.MEDIA != t {
		return nil, errors.New("invalid media type")
	}

	return playlist.(*m3u8.MediaPlaylist), nil
}