package photos

import (
	"bufio"
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"galo/internal/auth"
	"galo/internal/httpx"
	"galo/internal/models"
	"galo/internal/roles"
	"galo/internal/sse"
	"galo/internal/storage"
)

type AlbumAccess interface {
	Access(ctx context.Context, albumID, userID string) (*models.Album, string, error)
	// NotifyAlbumChanged announces a change to the album's photo composition on
	// the recipients' personal streams (album cards and counts update live).
	NotifyAlbumChanged(ctx context.Context, albumID string)
}

type Service struct {
	store   Repository
	albums  AlbumAccess
	storage storage.Backend
	hub     *sse.Hub

	imageMax     int64
	videoMax     int64
	videoEnabled bool
	tempDir      string
}

func NewService(store Repository, albums AlbumAccess, storage storage.Backend, hub *sse.Hub) *Service {
	return &Service{
		store:        store,
		albums:       albums,
		storage:      storage,
		hub:          hub,
		imageMax:     100 << 20,
		videoMax:     2 << 30,
		videoEnabled: true,
	}
}

// SetUploadLimits overrides the per-kind upload size limits.
func (s *Service) SetUploadLimits(imageMax, videoMax int64) {
	if imageMax > 0 {
		s.imageMax = imageMax
	}
	if videoMax > 0 {
		s.videoMax = videoMax
	}
}

// SetVideoEnabled controls whether video uploads are accepted. It is false when
// the ffmpeg/ffprobe toolchain is unavailable.
func (s *Service) SetVideoEnabled(enabled bool) { s.videoEnabled = enabled }

// SetTempDir sets where upload spool files are written (empty = system temp).
func (s *Service) SetTempDir(dir string) { s.tempDir = dir }

// MaxUploadSize returns the largest per-file limit across media kinds, for the
// request body cap.
func (s *Service) MaxUploadSize() int64 {
	if s.videoMax > s.imageMax {
		return s.videoMax
	}
	return s.imageMax
}

type UploadInput struct {
	AlbumID  string
	UserID   string
	Filename string
	MimeType string
	// Reader is the upload stream. When nil, Data is used instead.
	Reader io.Reader
	// Size is the declared payload size when known (0 when unknown).
	Size int64
	// Data is an optional in-memory payload for callers that already hold it.
	Data []byte
}

func (in UploadInput) reader() io.Reader {
	if in.Reader != nil {
		return in.Reader
	}
	return bytes.NewReader(in.Data)
}

func (in UploadInput) declaredSize() int64 {
	if in.Size > 0 {
		return in.Size
	}
	return int64(len(in.Data))
}

func (s *Service) Upload(ctx context.Context, in UploadInput) (*models.Photo, error) {
	_, role, err := s.albums.Access(ctx, in.AlbumID, in.UserID)
	if err != nil {
		return nil, err
	}
	if !roles.CanUpload(role) {
		return nil, httpx.Forbidden("forbidden", "you do not have permission to upload photos")
	}

	br := bufio.NewReader(in.reader())
	head, _ := br.Peek(512)
	kind, mime := resolveMedia(in.MimeType, in.Filename, head)
	if kind == "" {
		return nil, httpx.BadRequest("invalid_file", "file is not an image or video")
	}
	if kind == KindVideo && !s.videoEnabled {
		return nil, httpx.BadRequest("video_disabled", "video upload is not available")
	}
	limit := s.imageMax
	if kind == KindVideo {
		limit = s.videoMax
	}
	if sz := in.declaredSize(); sz > limit {
		return nil, uploadTooLarge(kind, limit)
	}

	// Spool to a temporary file, computing size and checksum without holding the
	// whole payload in memory. LimitReader enforces the cap even when the
	// declared size is unknown.
	tmp, err := os.CreateTemp(s.tempDir, "upload-*")
	if err != nil {
		return nil, err
	}
	tmpName := tmp.Name()
	defer func() { _ = os.Remove(tmpName) }()

	hasher := sha256.New()
	written, err := io.Copy(io.MultiWriter(tmp, hasher), io.LimitReader(br, limit+1))
	if err != nil {
		_ = tmp.Close()
		return nil, err
	}
	if err := tmp.Close(); err != nil {
		return nil, err
	}
	if written > limit {
		return nil, uploadTooLarge(kind, limit)
	}

	var width, height int
	var durationMS int64
	attrs := map[string]any{}
	var meta exifInfo
	if kind == KindImage {
		data, err := os.ReadFile(tmpName)
		if err != nil {
			return nil, err
		}
		w, h, ok := inspect(data)
		if !ok {
			return nil, httpx.BadRequest("invalid_image", "could not decode image")
		}
		width, height = w, h
		meta = extractEXIF(data)
		attrs = meta.Attributes
		if attrs == nil {
			attrs = map[string]any{}
		}
	}

	ext := strings.ToLower(filepath.Ext(in.Filename))
	if ext == "" {
		ext = ".bin"
	}

	photoID := auth.NewID()
	objectID := auth.NewID()
	key := objectKey(objectID, RoleOriginal, ext)

	p := &models.Photo{
		ID:               photoID,
		AlbumID:          in.AlbumID,
		UploaderID:       in.UserID,
		StorageKey:       key,
		OriginalFilename: in.Filename,
		Size:             written,
		Width:            width,
		Height:           height,
		Kind:             kind,
		DurationMS:       durationMS,
		MimeType:         mime,
		TakenAt:          meta.TakenAt,
		Latitude:         meta.Latitude,
		Longitude:        meta.Longitude,
		EXIF:             attrs,
	}
	obj := &Object{
		ID:         objectID,
		StorageKey: key,
		MimeType:   mime,
		Size:       written,
		Width:      width,
		Height:     height,
		Checksum:   hex.EncodeToString(hasher.Sum(nil)),
	}

	// The metadata layer is the ledger of record: the row is written first,
	// then the bytes are stored, then the object is activated.
	if err := s.store.CreateWithOriginal(ctx, p, obj); err != nil {
		return nil, err
	}
	file, err := os.Open(tmpName)
	if err != nil {
		_ = s.store.DeleteUpload(ctx, photoID, objectID)
		return nil, err
	}
	putErr := s.storage.Put(ctx, key, file, written, mime)
	file.Close()
	if putErr != nil {
		_ = s.store.DeleteUpload(ctx, photoID, objectID)
		return nil, putErr
	}
	if err := s.store.ActivateObject(ctx, objectID); err != nil {
		return nil, err
	}

	// The first photo uploaded to an album becomes its default cover.
	s.store.SetCoverIfEmpty(ctx, in.AlbumID, p.ID)

	if err := s.attachURLs(ctx, p); err != nil {
		return nil, err
	}
	// The photo appears in the album: subscribers insert it, and the album's
	// recipients see the new count (and cover, if this was the first photo).
	s.hub.Publish(in.AlbumID, "photo.created", p)
	s.albums.NotifyAlbumChanged(ctx, in.AlbumID)
	return p, nil
}

// resolveMedia determines the media kind and effective MIME type of an upload.
// It prefers the declared MIME type, falls back to sniffing the leading bytes,
// then to the file extension.
func resolveMedia(declared, filename string, head []byte) (kind, outMime string) {
	kind = kindFor(declared, filename)
	if kind == "" && len(head) > 0 {
		detected := http.DetectContentType(head)
		kind = kindFor(detected, filename)
		if declared == "" {
			declared = detected
		}
	}
	if kind == "" {
		return "", ""
	}
	outMime = declared
	if !strings.HasPrefix(outMime, kind+"/") {
		if byExt := mime.TypeByExtension(filepath.Ext(filename)); byExt != "" {
			outMime = byExt
		}
	}
	if outMime == "" || !strings.HasPrefix(outMime, kind+"/") {
		if kind == KindVideo {
			outMime = "video/mp4"
		} else {
			outMime = "image/jpeg"
		}
	}
	return kind, outMime
}

// kindFor classifies a MIME type or file extension as image or video.
func kindFor(mimeType, filename string) string {
	switch {
	case strings.HasPrefix(mimeType, "image/"):
		return KindImage
	case strings.HasPrefix(mimeType, "video/"):
		return KindVideo
	}
	switch strings.ToLower(filepath.Ext(filename)) {
	case ".mp4", ".m4v", ".mov", ".mkv", ".webm", ".avi", ".mpg", ".mpeg", ".3gp":
		return KindVideo
	case ".jpg", ".jpeg", ".png", ".gif", ".webp", ".heic", ".heif", ".tiff", ".tif", ".bmp", ".avif":
		return KindImage
	}
	return ""
}

func uploadTooLarge(kind string, limit int64) error {
	return httpx.NewError(http.StatusRequestEntityTooLarge, "file_too_large",
		fmt.Sprintf("file exceeds the maximum %s upload size (%s)", kind, humanSize(limit)))
}

func humanSize(n int64) string {
	switch {
	case n >= 1<<30:
		return fmt.Sprintf("%d GB", n>>30)
	case n >= 1<<20:
		return fmt.Sprintf("%d MB", n>>20)
	case n >= 1<<10:
		return fmt.Sprintf("%d KB", n>>10)
	default:
		return fmt.Sprintf("%d B", n)
	}
}

func (s *Service) attachURLs(ctx context.Context, p *models.Photo) error {
	if p.StorageKey != "" {
		url, err := s.storage.URL(ctx, p.StorageKey)
		if err != nil {
			return err
		}
		p.OriginalURL = url
		p.DownloadURL = url
	}
	if p.ThumbKey != "" {
		if url, err := s.storage.URL(ctx, p.ThumbKey); err == nil {
			p.ThumbURL = url
		}
	}
	if p.MediumKey != "" {
		if url, err := s.storage.URL(ctx, p.MediumKey); err == nil {
			p.MediumURL = url
		}
	}
	if p.PreviewKey != "" {
		if url, err := s.storage.URL(ctx, p.PreviewKey); err == nil {
			p.PreviewURL = url
		}
	}
	if p.PlaybackKey != "" {
		if url, err := s.storage.URL(ctx, p.PlaybackKey); err == nil {
			p.PlaybackURL = url
		}
	}
	return nil
}

func (s *Service) List(ctx context.Context, albumID, userID, cursor string, since *time.Time, limit int) ([]models.Photo, string, error) {
	if _, _, err := s.albums.Access(ctx, albumID, userID); err != nil {
		return nil, "", err
	}
	out, err := s.store.List(ctx, ListParams{
		AlbumID: albumID,
		Viewer:  userID,
		Cursor:  cursor,
		Since:   since,
		Limit:   limit,
	})
	if err != nil {
		return nil, "", err
	}
	for i := range out {
		_ = s.attachURLs(ctx, &out[i])
	}
	next := ""
	if since == nil && len(out) == limit && limit > 0 {
		next = out[len(out)-1].ID
	}
	return out, next, nil
}

// ListPublic lists photos for a share link (access already validated by token).
func (s *Service) ListPublic(ctx context.Context, albumID, cursor string, since *time.Time, limit int) ([]models.Photo, string, error) {
	out, err := s.store.List(ctx, ListParams{
		AlbumID: albumID,
		Viewer:  "",
		Cursor:  cursor,
		Since:   since,
		Limit:   limit,
	})
	if err != nil {
		return nil, "", err
	}
	for i := range out {
		_ = s.attachURLs(ctx, &out[i])
	}
	next := ""
	if since == nil && len(out) == limit && limit > 0 {
		next = out[len(out)-1].ID
	}
	return out, next, nil
}

// GetPublic returns a single photo for a share link.
func (s *Service) GetPublic(ctx context.Context, photoID string) (*models.Photo, error) {
	p, err := s.store.GetByID(ctx, photoID, "")
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return nil, httpx.NotFound("photo_not_found", "photo not found")
		}
		return nil, err
	}
	if p.DeletedAt != nil {
		return nil, httpx.NotFound("photo_not_found", "photo not found")
	}
	if err := s.attachURLs(ctx, p); err != nil {
		return nil, err
	}
	return p, nil
}

// DownloadPublic returns a signed original URL for a share link.
func (s *Service) DownloadPublic(ctx context.Context, photoID string) (string, error) {
	p, err := s.GetPublic(ctx, photoID)
	if err != nil {
		return "", err
	}
	return s.storage.URL(ctx, p.StorageKey)
}

func (s *Service) Get(ctx context.Context, photoID, userID string) (*models.Photo, error) {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return nil, httpx.NotFound("photo_not_found", "photo not found")
		}
		return nil, err
	}
	if p.DeletedAt != nil {
		return nil, httpx.NotFound("photo_not_found", "photo not found")
	}
	if _, _, err := s.albums.Access(ctx, p.AlbumID, userID); err != nil {
		return nil, err
	}
	if err := s.attachURLs(ctx, p); err != nil {
		return nil, err
	}
	return p, nil
}

func (s *Service) Download(ctx context.Context, photoID, userID string) (string, error) {
	p, err := s.Get(ctx, photoID, userID)
	if err != nil {
		return "", err
	}
	url, err := s.storage.URL(ctx, p.StorageKey)
	if err != nil {
		return "", err
	}
	return url, nil
}

func (s *Service) Rename(ctx context.Context, photoID, userID, filename string) (*models.Photo, error) {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return nil, httpx.NotFound("photo_not_found", "photo not found")
		}
		return nil, err
	}
	_, role, err := s.albums.Access(ctx, p.AlbumID, userID)
	if err != nil {
		return nil, err
	}
	own := p.UploaderID == userID
	if !(roles.CanDeleteAnyPhoto(role) || (own && roles.CanDeleteOwnPhoto(role))) {
		return nil, httpx.Forbidden("forbidden", "you cannot rename this photo")
	}
	name := strings.TrimSpace(filename)
	if name == "" {
		return nil, httpx.BadRequest("invalid_filename", "filename is required")
	}
	if len(name) > 255 {
		name = name[:255]
	}
	if err := s.store.UpdateFilename(ctx, photoID, name); err != nil {
		return nil, err
	}
	p.OriginalFilename = name
	if err := s.attachURLs(ctx, p); err != nil {
		return nil, err
	}
	s.hub.Publish(p.AlbumID, "photo.updated", p)
	return p, nil
}

func (s *Service) Delete(ctx context.Context, photoID, userID string) error {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return httpx.NotFound("photo_not_found", "photo not found")
		}
		return err
	}
	_, role, err := s.albums.Access(ctx, p.AlbumID, userID)
	if err != nil {
		return err
	}
	if !canDeletePhoto(role, p.UploaderID == userID) {
		return httpx.Forbidden("forbidden", "you cannot delete this photo")
	}
	if p.DeletedAt != nil {
		return nil
	}
	if err := s.store.SetDeleted(ctx, photoID, true); err != nil {
		return err
	}
	// A trashed cover leaves the album without one.
	s.store.ClearCoverIfMatches(ctx, p.AlbumID, photoID)
	s.publishDeleted(p)
	s.albums.NotifyAlbumChanged(ctx, p.AlbumID)
	return nil
}

func canDeletePhoto(role string, own bool) bool {
	return roles.CanDeleteAnyPhoto(role) || (own && roles.CanDeleteOwnPhoto(role))
}

func (s *Service) publishDeleted(p *models.Photo) {
	s.hub.Publish(p.AlbumID, "photo.deleted", map[string]string{
		"id": p.ID, "album_id": p.AlbumID, "uploader_id": p.UploaderID,
	})
}

// DeleteBatch moves the given photos to the trash. It skips photos the user cannot delete.
func (s *Service) DeleteBatch(ctx context.Context, ids []string, userID string) (int, error) {
	deleted := 0
	for _, id := range ids {
		if err := s.Delete(ctx, id, userID); err != nil {
			continue
		}
		deleted++
	}
	return deleted, nil
}

// Restore returns a photo from the trash back to its album.
// Restore returns a photo from the trash back to an album. When targetAlbumID is
// empty the photo goes back to its own album; if that album is gone, an
// album_required error is returned so the client can prompt for a target.
func (s *Service) Restore(ctx context.Context, photoID, userID, targetAlbumID string) (*models.Photo, error) {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return nil, httpx.NotFound("photo_not_found", "photo not found")
		}
		return nil, err
	}

	if targetAlbumID != "" {
		_, role, err := s.albums.Access(ctx, targetAlbumID, userID)
		if err != nil {
			return nil, err
		}
		if !roles.CanUpload(role) {
			return nil, httpx.Forbidden("forbidden", "you cannot add photos to the target album")
		}
		if err := s.store.RestoreToAlbum(ctx, photoID, targetAlbumID); err != nil {
			return nil, err
		}
		p.AlbumID = targetAlbumID
		p.DeletedAt = nil
	} else {
		if p.AlbumID == "" {
			return nil, httpx.BadRequest("album_required", "choose an album to restore this photo into")
		}
		exists, err := s.store.AlbumExists(ctx, p.AlbumID)
		if err != nil {
			return nil, err
		}
		if !exists {
			return nil, httpx.BadRequest("album_required", "choose an album to restore this photo into")
		}
		_, role, err := s.albums.Access(ctx, p.AlbumID, userID)
		if err != nil {
			return nil, err
		}
		if !canDeletePhoto(role, p.UploaderID == userID) {
			return nil, httpx.Forbidden("forbidden", "you cannot restore this photo")
		}
		if p.DeletedAt != nil {
			if err := s.store.SetDeleted(ctx, photoID, false); err != nil {
				return nil, err
			}
		}
		p.DeletedAt = nil
	}

	if err := s.attachURLs(ctx, p); err != nil {
		return nil, err
	}
	if p.AlbumID != "" {
		s.hub.Publish(p.AlbumID, "photo.created", p)
		s.albums.NotifyAlbumChanged(ctx, p.AlbumID)
	}
	return p, nil
}

// PermanentDelete removes the photo row; stored objects are deleted only when no
// other album references the same storage key.
func (s *Service) PermanentDelete(ctx context.Context, photoID, userID string) error {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return httpx.NotFound("photo_not_found", "photo not found")
		}
		return err
	}
	if p.AlbumID == "" {
		// A photo whose album was deleted only has its uploader to vouch for it.
		if p.UploaderID != userID {
			return httpx.Forbidden("forbidden", "you cannot delete this photo")
		}
	} else {
		_, role, err := s.albums.Access(ctx, p.AlbumID, userID)
		if err != nil {
			return err
		}
		if !canDeletePhoto(role, p.UploaderID == userID) {
			return httpx.Forbidden("forbidden", "you cannot delete this photo")
		}
	}
	objectIDs, err := s.store.PhotoObjectIDs(ctx, photoID)
	if err != nil {
		return err
	}
	if err := s.store.HardDelete(ctx, photoID); err != nil {
		return err
	}
	if p.AlbumID != "" {
		s.publishDeleted(p)
		s.albums.NotifyAlbumChanged(ctx, p.AlbumID)
	}
	// Mark objects that no longer have any binding for garbage collection.
	// The background worker removes the blobs from storage.
	for _, oid := range objectIDs {
		if n, err := s.store.ObjectRefCount(ctx, oid); err == nil && n == 0 {
			_ = s.store.MarkObjectDeleting(ctx, oid)
		}
	}
	return nil
}

// EmptyTrash permanently deletes every trashed photo the user may remove,
// skipping the rest, and returns how many were deleted.
func (s *Service) EmptyTrash(ctx context.Context, userID string) (int, error) {
	items, err := s.store.ListTrashIdentities(ctx, userID)
	if err != nil {
		return 0, err
	}
	deleted := 0
	for _, it := range items {
		if err := s.PermanentDelete(ctx, it.ID, userID); err != nil {
			continue
		}
		deleted++
	}
	return deleted, nil
}

// MoveBatch moves photos to another album (metadata only; stored objects untouched).
func (s *Service) MoveBatch(ctx context.Context, ids []string, userID, targetAlbumID string) (int, error) {
	_, targetRole, err := s.albums.Access(ctx, targetAlbumID, userID)
	if err != nil {
		return 0, err
	}
	if !roles.CanUpload(targetRole) {
		return 0, httpx.Forbidden("forbidden", "you cannot add photos to the target album")
	}
	moved := 0
	changed := map[string]struct{}{}
	for _, id := range ids {
		p, err := s.store.GetByID(ctx, id, userID)
		if err != nil || p.DeletedAt != nil {
			continue
		}
		oldAlbum := p.AlbumID
		if oldAlbum == targetAlbumID {
			continue
		}
		_, srcRole, err := s.albums.Access(ctx, oldAlbum, userID)
		if err != nil {
			continue
		}
		if !canDeletePhoto(srcRole, p.UploaderID == userID) {
			continue
		}
		if err := s.store.UpdateAlbum(ctx, id, targetAlbumID); err != nil {
			continue
		}
		// Moving a cover photo out of its album leaves the album without one.
		s.store.ClearCoverIfMatches(ctx, oldAlbum, id)
		p.AlbumID = targetAlbumID
		s.hub.Publish(oldAlbum, "photo.deleted", map[string]string{
			"id": p.ID, "album_id": oldAlbum, "uploader_id": p.UploaderID,
		})
		if err := s.attachURLs(ctx, p); err == nil {
			s.hub.Publish(targetAlbumID, "photo.created", p)
		}
		changed[oldAlbum] = struct{}{}
		changed[targetAlbumID] = struct{}{}
		moved++
	}
	// One album.updated per affected album, not per photo.
	for albumID := range changed {
		s.albums.NotifyAlbumChanged(ctx, albumID)
	}
	return moved, nil
}

// CopyBatch clones photos into another album (metadata only; stored objects shared).
func (s *Service) CopyBatch(ctx context.Context, ids []string, userID, targetAlbumID string) ([]models.Photo, error) {
	_, targetRole, err := s.albums.Access(ctx, targetAlbumID, userID)
	if err != nil {
		return nil, err
	}
	if !roles.CanUpload(targetRole) {
		return nil, httpx.Forbidden("forbidden", "you cannot add photos to the target album")
	}
	out := []models.Photo{}
	for _, id := range ids {
		src, err := s.store.GetByID(ctx, id, userID)
		if err != nil || src.DeletedAt != nil {
			continue
		}
		if _, _, err := s.albums.Access(ctx, src.AlbumID, userID); err != nil {
			continue
		}
		newID := auth.NewID()
		if err := s.store.Clone(ctx, src, targetAlbumID, userID, newID); err != nil {
			continue
		}
		clone, err := s.store.GetByID(ctx, newID, userID)
		if err != nil {
			continue
		}
		if err := s.attachURLs(ctx, clone); err != nil {
			continue
		}
		s.store.SetCoverIfEmpty(ctx, targetAlbumID, newID)
		s.hub.Publish(targetAlbumID, "photo.created", clone)
		out = append(out, *clone)
	}
	if len(out) > 0 {
		s.albums.NotifyAlbumChanged(ctx, targetAlbumID)
	}
	return out, nil
}

// Trash lists soft-deleted photos from all albums the user belongs to.
func (s *Service) Trash(ctx context.Context, userID string) ([]models.Photo, error) {
	out, err := s.store.ListTrash(ctx, userID)
	if err != nil {
		return nil, err
	}
	for i := range out {
		_ = s.attachURLs(ctx, &out[i])
	}
	return out, nil
}

// TrashCount returns the number of photos in the user's trash.
func (s *Service) TrashCount(ctx context.Context, userID string) (int, error) {
	return s.store.TrashCount(ctx, userID)
}

// Tags lists the user's tags, optionally filtered by a search query.
func (s *Service) Tags(ctx context.Context, userID, q string) ([]models.Tag, error) {
	return s.store.ListTags(ctx, userID, q)
}

func (s *Service) taggablePhoto(ctx context.Context, photoID, userID string) (*models.Photo, error) {
	p, err := s.store.GetByID(ctx, photoID, userID)
	if err != nil {
		if errors.Is(err, ErrNotFound) {
			return nil, httpx.NotFound("photo_not_found", "photo not found")
		}
		return nil, err
	}
	if p.DeletedAt != nil {
		return nil, httpx.NotFound("photo_not_found", "photo not found")
	}
	if p.AlbumID == "" {
		return nil, httpx.NotFound("photo_not_found", "photo not found")
	}
	if _, _, err := s.albums.Access(ctx, p.AlbumID, userID); err != nil {
		return nil, err
	}
	return p, nil
}

// AddTag attaches a tag (created on demand) to a photo and returns the refreshed photo.
func (s *Service) AddTag(ctx context.Context, photoID, userID, name string) (*models.Photo, error) {
	if _, err := s.taggablePhoto(ctx, photoID, userID); err != nil {
		return nil, err
	}
	tag, err := s.store.EnsureTag(ctx, userID, name)
	if err != nil {
		return nil, httpx.BadRequest("invalid_tag", "tag name is required")
	}
	if err := s.store.AttachTag(ctx, photoID, tag.ID); err != nil {
		return nil, err
	}
	return s.Get(ctx, photoID, userID)
}

// RemoveTag detaches one of the user's tags from a photo.
func (s *Service) RemoveTag(ctx context.Context, photoID, userID, tagID string) (*models.Photo, error) {
	if _, err := s.taggablePhoto(ctx, photoID, userID); err != nil {
		return nil, err
	}
	owned, err := s.store.TagOwnedBy(ctx, tagID, userID)
	if err != nil {
		return nil, err
	}
	if !owned {
		return nil, httpx.NotFound("tag_not_found", "tag not found")
	}
	if err := s.store.DetachTag(ctx, photoID, tagID); err != nil {
		return nil, err
	}
	return s.Get(ctx, photoID, userID)
}