memby/server/internal/api/extras.go

package api

import (
	"context"
	"encoding/json"
	"net/http"
	"sync"

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

// extrasResponse is the Extras tab: featurettes, deleted scenes, interviews and the local
// trailer, as Emby's own item JSON so the television's single BaseItem model decodes it.
type extrasResponse struct {
	Items []json.RawMessage `json:"items"`
}

// handleExtras joins the two lists Emby keeps an item's supplementary video in.
//
// It has to be a join, because Emby answers the question in two places and neither includes
// the other: `SpecialFeatures` holds the featurettes and deleted scenes, `LocalTrailers`
// holds the trailer, and a detail page asking only one of them shows an Extras tab missing
// the thing most titles that have anything actually have.
//
// Done here rather than on the television for the ordinary reason: in gateway mode the set
// holds no Emby credential. Doing it here also means one request instead of two on the path
// that matters — the tab is probed on every detail page open.
func (s *Server) handleExtras(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
	}
	// Cached for the household rather than per viewer, and outside the namespace a
	// playback stop invalidates: what a film ships with is a fact about the film, and
	// nothing in this response carries user data. Empty answers included — most of a
	// library has no extras at all and every detail page asks, so the "no" is the entry
	// worth keeping.
	key := cache.MetadataKey("extras:v2:" + itemID)
	body, hit, err := s.cachedRead(ctx, key, s.cfg.ItemTTL,
		func(ctx context.Context) (json.RawMessage, error) {
			return s.extras(ctx, credentials(sess), itemID)
		})
	if err != nil {
		s.writeUpstreamError(ctx, w, err, "could not load extras")
		return
	}
	writeCached(w, hit, body)
}

// extras joins the two places Emby keeps them.
//
// The two lookups are independent and are made together. They used to run in turn, which
// on a detail page open — where this is one of five requests the television makes at once
// — was one round trip of pure waiting for no reason at all.
//
// Neither list failing is fatal, and only both failing is a failure worth reporting: a
// title can perfectly well have a trailer and no special features, or the reverse, and an
// Extras tab withheld because one of two lookups was unwell is the worse outcome.
func (s *Server) extras(
	ctx context.Context, cred emby.Credentials, itemID string,
) (json.RawMessage, error) {
	var (
		trailers   *emby.ItemsResult
		trailerErr error
		features   *emby.ItemsResult
		featureErr error
		wg         sync.WaitGroup
	)
	wg.Add(2)
	go func() {
		defer wg.Done()
		trailers, trailerErr = s.emby.LocalTrailers(timing.WithLabel(ctx, "emby.trailers"), cred, itemID)
	}()
	go func() {
		defer wg.Done()
		features, featureErr = s.emby.SpecialFeatures(timing.WithLabel(ctx, "emby.features"), cred, itemID)
	}()
	wg.Wait()

	if trailerErr != nil && featureErr != nil {
		return nil, featureErr
	}
	var items []json.RawMessage
	if trailerErr == nil && trailers != nil {
		items = append(items, trailers.Items...)
	}
	if featureErr == nil && features != nil {
		items = append(items, features.Items...)
	}
	return json.Marshal(extrasResponse{Items: nonNilRaws(dedupeExtras(items))})
}

// dedupeExtras drops the same file appearing in both lists, in first-seen order.
//
// A trailer filed as a special feature *and* as a local trailer is an ordinary way for a
// library to be laid out, and the television renders these into a keyed grid — which throws
// on a repeated key rather than merely looking wrong. Anything without an id is dropped for
// the same reason.
func dedupeExtras(items []json.RawMessage) []json.RawMessage {
	seen := make(map[string]struct{}, len(items))
	out := make([]json.RawMessage, 0, len(items))
	for _, raw := range items {
		var identified struct {
			ID string `json:"Id"`
		}
		if err := json.Unmarshal(raw, &identified); err != nil || identified.ID == "" {
			continue
		}
		if _, repeated := seen[identified.ID]; repeated {
			continue
		}
		seen[identified.ID] = struct{}{}
		out = append(out, raw)
	}
	return out
}