s3 support

internal/domain/media_refs.go

@@ -0,0 +1,90 @@
+package domain
+
+// MediaKind identifies which table a media_references row points into.
+type MediaKind string
+
+const (
+	MediaKindDocument MediaKind = "document"
+	MediaKindPhoto    MediaKind = "photo"
+)
+
+// MediaRefKind identifies why a document/photo is still considered "live" --
+// each distinct kind of place that can hold a durable pointer to media gets
+// its own ref_kind, so removing one kind of reference (e.g. a deleted
+// message) doesn't accidentally drop a still-live reference of another kind
+// (e.g. the same document also set as someone's profile photo).
+type MediaRefKind string
+
+const (
+	MediaRefKindMessageBox     MediaRefKind = "message_box"
+	MediaRefKindChannelMessage MediaRefKind = "channel_message"
+	MediaRefKindProfilePhoto   MediaRefKind = "profile_photo"
+	MediaRefKindStickerSet     MediaRefKind = "sticker_set"
+	MediaRefKindGift           MediaRefKind = "gift"
+)
+
+// MediaReference is one live pointer to a document/photo. GC (the storage
+// retention sweep) only considers a document/photo eligible for deletion
+// once every reference to it has been removed.
+type MediaReference struct {
+	Kind    MediaKind
+	MediaID int64
+	RefKind MediaRefKind
+	RefKey  string
+}
+
+// OrphanCandidate is a document/photo whose last reference has been removed
+// (orphaned_at is set) and is old enough to be considered for the storage
+// retention sweep.
+type OrphanCandidate struct {
+	Kind       MediaKind
+	MediaID    int64
+	Backend    MediaBackend
+	ObjectKey  string
+	Size       int64
+	OrphanedAt int64 // unix seconds
+}
+
+// MediaRefTarget identifies one document/photo embedded in a message's media
+// snapshot.
+type MediaRefTarget struct {
+	Kind MediaKind
+	ID   int64
+}
+
+// ExtractMediaRefTargets returns every document/photo id embedded in a
+// message's media snapshot (including nested ones -- a live photo's video
+// document, a webpage preview's photo), deduplicated. Used to register/drop
+// media_references rows when a message carrying this media is
+// created/edited/deleted.
+func ExtractMediaRefTargets(media *MessageMedia) []MediaRefTarget {
+	if media == nil {
+		return nil
+	}
+	seen := make(map[MediaRefTarget]struct{}, 2)
+	var out []MediaRefTarget
+	add := func(kind MediaKind, id int64) {
+		if id == 0 {
+			return
+		}
+		t := MediaRefTarget{Kind: kind, ID: id}
+		if _, ok := seen[t]; ok {
+			return
+		}
+		seen[t] = struct{}{}
+		out = append(out, t)
+	}
+	if media.Photo != nil {
+		add(MediaKindPhoto, media.Photo.ID)
+	}
+	if media.Document != nil {
+		add(MediaKindDocument, media.Document.ID)
+	}
+	if media.LivePhotoVideo != nil {
+		add(MediaKindDocument, media.LivePhotoVideo.ID)
+	}
+	if media.WebPage != nil && media.WebPage.Photo != nil {
+		add(MediaKindPhoto, media.WebPage.Photo.ID)
+	}
+	return out
+}