feat: fallback to TMDB external_ids when Trakt rejects tmdbId

When Trakt returns a non-404 error (e.g. 403) for a tmdbId lookup,
fetch the imdbId from TMDB's /external_ids endpoint and retry the
Trakt call using the imdbId. Trakt often knows a movie/show by its
imdbId even when it does not recognise the tmdbId.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

media/movie.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/l3uddz/nabarr/media/trakt"
@@ -22,7 +23,24 @@ func (c *Client) GetMovieInfo(item *FeedItem) (*Item, error) {
 		if errors.Is(err, trakt.ErrItemNotFound) {
 			return nil, fmt.Errorf("trakt: get movie: movie with %sId %q: %w", mdp, mdi, ErrItemNotFound)
 		}
-		return nil, fmt.Errorf("trakt: get movie: movie with %sId %q: %w", mdp, mdi, err)
+
+		// fallback: if we queried by tmdbId and have TMDB configured, try fetching
+		// the imdbId from TMDB and retry Trakt — Trakt may know the movie by imdbId
+		// even when it doesn't recognise the tmdbId (returns 403).
+		if c.tmdb != nil && mdp == "tmdb" {
+			if tmdbIdInt, convErr := strconv.Atoi(mdi); convErr == nil {
+				if imdbId, extErr := c.tmdb.GetMovieExternalIds(tmdbIdInt); extErr == nil && strings.HasPrefix(imdbId, "tt") {
+					t, err = c.trakt.GetMovie("imdb", imdbId)
+				}
+			}
+		}
+
+		if err != nil {
+			if errors.Is(err, trakt.ErrItemNotFound) {
+				return nil, fmt.Errorf("trakt: get movie: movie with %sId %q: %w", mdp, mdi, ErrItemNotFound)
+			}
+			return nil, fmt.Errorf("trakt: get movie: movie with %sId %q: %w", mdp, mdi, err)
+		}
 	}
 
 	// transform trakt info

media/show.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"strings"
 
 	"github.com/l3uddz/nabarr/media/trakt"
 )
@@ -21,7 +22,24 @@ func (c *Client) GetShowInfo(item *FeedItem) (*Item, error) {
 		if errors.Is(err, trakt.ErrItemNotFound) {
 			return nil, fmt.Errorf("trakt: get show: show with %sId %q: %w", mdp, mdi, ErrItemNotFound)
 		}
-		return nil, fmt.Errorf("trakt: get show: show with %sId %q: %w", mdp, mdi, err)
+
+		// fallback: if we queried by tmdbId and have TMDB configured, try fetching
+		// the imdbId from TMDB and retry Trakt — Trakt may know the show by imdbId
+		// even when it doesn't recognise the tmdbId (returns 403).
+		if c.tmdb != nil && mdp == "tmdb" {
+			if tmdbIdInt, convErr := strconv.Atoi(mdi); convErr == nil {
+				if imdbId, extErr := c.tmdb.GetShowExternalIds(tmdbIdInt); extErr == nil && strings.HasPrefix(imdbId, "tt") {
+					t, err = c.trakt.GetShow("imdb", imdbId)
+				}
+			}
+		}
+
+		if err != nil {
+			if errors.Is(err, trakt.ErrItemNotFound) {
+				return nil, fmt.Errorf("trakt: get show: show with %sId %q: %w", mdp, mdi, ErrItemNotFound)
+			}
+			return nil, fmt.Errorf("trakt: get show: show with %sId %q: %w", mdp, mdi, err)
+		}
 	}
 
 	// transform trakt info to MediaItem

media/tmdb/media.go

@@ -50,6 +50,48 @@ func (c *Client) SearchMovies(title string, year int) (int, error) {
 	return b.Results[0].Id, nil
 }
 
+func (c *Client) GetMovieExternalIds(tmdbId int) (string, error) {
+	reqUrl := util.JoinURL(c.apiURL, "movie", strconv.Itoa(tmdbId), "external_ids") + "?api_key=" + c.apiKey
+
+	resp, err := rek.Get(reqUrl, rek.Client(c.http))
+	if err != nil {
+		return "", fmt.Errorf("request movie external ids: %w", err)
+	}
+	defer resp.Body().Close()
+
+	if resp.StatusCode() != 200 {
+		return "", fmt.Errorf("validate movie external ids response: %s", resp.Status())
+	}
+
+	b := new(externalIdsResponse)
+	if err := json.NewDecoder(resp.Body()).Decode(b); err != nil {
+		return "", fmt.Errorf("decode movie external ids response: %w", err)
+	}
+
+	return b.ImdbId, nil
+}
+
+func (c *Client) GetShowExternalIds(tmdbId int) (string, error) {
+	reqUrl := util.JoinURL(c.apiURL, "tv", strconv.Itoa(tmdbId), "external_ids") + "?api_key=" + c.apiKey
+
+	resp, err := rek.Get(reqUrl, rek.Client(c.http))
+	if err != nil {
+		return "", fmt.Errorf("request show external ids: %w", err)
+	}
+	defer resp.Body().Close()
+
+	if resp.StatusCode() != 200 {
+		return "", fmt.Errorf("validate show external ids response: %s", resp.Status())
+	}
+
+	b := new(externalIdsResponse)
+	if err := json.NewDecoder(resp.Body()).Decode(b); err != nil {
+		return "", fmt.Errorf("decode show external ids response: %w", err)
+	}
+
+	return b.ImdbId, nil
+}
+
 func (c *Client) SearchShows(title string, year int) (int, error) {
 	vals := url.Values{
 		"api_key": []string{c.apiKey},

media/tmdb/struct.go

@@ -11,3 +11,7 @@ type tvSearchResponse struct {
 		Id int `json:"id"`
 	} `json:"results"`
 }
+
+type externalIdsResponse struct {
+	ImdbId string `json:"imdb_id"`
+}