package api

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

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

// 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
	}
	key := cache.UserKey(sess.EmbyUserID, "extras:v1:"+itemID)
	if raw, err := s.cache.Get(ctx, key); err == nil {
		w.Header().Set("X-Memby-Cache", "hit")
		writeRaw(w, http.StatusOK, raw)
		return
	}

	cred := credentials(sess)
	// 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.
	var items []json.RawMessage
	trailerErr := error(nil)
	if result, err := s.emby.LocalTrailers(ctx, cred, itemID); err == nil {
		items = append(items, result.Items...)
	} else {
		trailerErr = err
	}
	featureErr := error(nil)
	if result, err := s.emby.SpecialFeatures(ctx, cred, itemID); err == nil {
		items = append(items, result.Items...)
	} else {
		featureErr = err
	}
	if trailerErr != nil && featureErr != nil {
		s.writeUpstreamError(ctx, w, featureErr, "could not load extras")
		return
	}

	items = dedupeExtras(items)
	body, err := json.Marshal(extrasResponse{Items: nonNilRaws(items)})
	if err != nil {
		writeError(w, http.StatusInternalServerError, "could not encode extras")
		return
	}
	// Cached for the ordinary item lifetime, 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.
	if err := s.cache.Set(ctx, key, body, s.cfg.ItemTTL); err != nil {
		s.loggerFor(ctx).Warn("extras cache write failed", "error", err)
	}
	w.Header().Set("X-Memby-Cache", "miss")
	writeRaw(w, http.StatusOK, body)
}

// 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
}