memby/server/internal/api/playback.go

package api

import (
	"context"
	"encoding/json"
	"net/http"
	"net/url"
	"strings"

	"github.com/ponzischeme89/memby/server/internal/emby"
	"github.com/ponzischeme89/memby/server/internal/store"
)

const ticksPerMillisecond = 10_000

type playbackResponse struct {
	ItemID           string `json:"itemId"`
	Title            string `json:"title"`
	URL              string `json:"url"`
	ResumePositionMs int64  `json:"resumePositionMs"`
}

type playbackReport struct {
	ItemID     string `json:"itemId"`
	PositionMs int64  `json:"positionMs"`
	IsPaused   bool   `json:"isPaused"`
}

// handlePlayback resolves what to actually play.
//
// This is logic the TV used to carry: a series resolves to its next-up episode (falling
// back to the first), and the returned URL points straight at Emby so the video stream
// never traverses the gateway.
func (s *Server) handlePlayback(w http.ResponseWriter, r *http.Request, sess store.Session) {
	ctx := r.Context()
	itemID := r.PathValue("id")
	if itemID == "" {
		writeError(w, http.StatusBadRequest, "item id is required")
		return
	}
	cred := credentials(sess)

	raw, err := s.emby.Item(ctx, cred, itemID, "RunTimeTicks,SeriesName")
	if err != nil {
		s.writeUpstreamError(w, err, "could not load the item")
		return
	}
	item, err := emby.Summarise(raw)
	if err != nil {
		writeError(w, http.StatusBadGateway, "unreadable item from emby")
		return
	}

	target := item
	title := item.Name

	if strings.EqualFold(item.Type, "Series") {
		episode, err := s.firstPlayableEpisode(ctx, cred, item.ID)
		if err != nil {
			s.writeUpstreamError(w, err, "could not find an episode to play")
			return
		}
		if episode == nil {
			writeError(w, http.StatusNotFound, "no episodes found for this series")
			return
		}
		target = *episode
		if episode.Name != "" {
			title = item.Name + " – " + episode.Name
		}
	}

	writeJSON(w, http.StatusOK, playbackResponse{
		ItemID:           target.ID,
		Title:            title,
		URL:              s.emby.StreamURL(cred, target.ID),
		ResumePositionMs: max64(target.UserData.PlaybackPositionTicks/ticksPerMillisecond, 0),
	})
}

// firstPlayableEpisode prefers the server's next-up choice and falls back to episode one.
func (s *Server) firstPlayableEpisode(ctx context.Context, cred emby.Credentials, seriesID string) (*emby.Summary, error) {
	nextUp, err := s.emby.NextUp(ctx, cred, url.Values{
		"SeriesId":       {seriesID},
		"Limit":          {"1"},
		"Fields":         {"RunTimeTicks"},
		"EnableUserData": {"true"},
	})
	if err == nil && len(nextUp.Items) > 0 {
		if summary, err := emby.Summarise(nextUp.Items[0]); err == nil {
			return &summary, nil
		}
	}

	episodes, err := s.emby.Episodes(ctx, cred, seriesID, url.Values{
		"Limit":          {"1"},
		"Fields":         {"RunTimeTicks"},
		"EnableUserData": {"true"},
	})
	if err != nil {
		return nil, err
	}
	if len(episodes.Items) == 0 {
		return nil, nil
	}
	summary, err := emby.Summarise(episodes.Items[0])
	if err != nil {
		return nil, err
	}
	return &summary, nil
}

// handlePlaybackReport forwards progress to Emby. Stopping invalidates the user's cache
// so Continue Watching reflects the new position on the next home load.
func (s *Server) handlePlaybackReport(w http.ResponseWriter, r *http.Request, sess store.Session) {
	phase := r.PathValue("phase")
	switch phase {
	case "started", "progress", "stopped":
	default:
		writeError(w, http.StatusNotFound, "unknown playback phase")
		return
	}

	var report playbackReport
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4<<10)).Decode(&report); err != nil {
		writeError(w, http.StatusBadRequest, "malformed request body")
		return
	}
	if report.ItemID == "" {
		writeError(w, http.StatusBadRequest, "itemId is required")
		return
	}

	err := s.emby.ReportPlayback(r.Context(), credentials(sess), phase, report.ItemID,
		max64(report.PositionMs, 0)*ticksPerMillisecond, report.IsPaused)
	if err != nil {
		// A dropped progress report is not worth failing playback over; log and accept.
		s.log.Warn("playback report failed", "phase", phase, "error", err)
	}

	if phase == "stopped" {
		if err := s.cache.InvalidateUser(r.Context(), sess.EmbyUserID); err != nil {
			s.log.Warn("cache invalidation failed", "error", err)
		}
		// Finishing something is the one event that genuinely changes viewing history,
		// so it is also the only thing that retires the recommendation rows.
		if err := s.cache.InvalidateRecommendations(r.Context(), sess.EmbyUserID); err != nil {
			s.log.Warn("recommendation invalidation failed", "error", err)
		}
	}
	w.WriteHeader(http.StatusNoContent)
}

func max64(v, floor int64) int64 {
	if v < floor {
		return floor
	}
	return v
}