meta

type Batcher interface {
	// BatchGet retrieves multiple FileMeta objects by their IDs. It must handle different versions for backward compatibility.
	BatchGet(ids []string) (map[string]FileMeta, error)
	// BatchUpdate overwrites multiple existing FileMeta objects.
	BatchUpdate(fileMetas map[string]FileMeta) error
}

type File struct {
	ID   string
	Meta FileMeta
}

type FileMeta interface {
	// CurrentVersion returns the version number of this metadata record.
	CurrentVersion() int32
	// Size returns the byte size of the file contents.
	Size() int64
	// ModTime returns when the contents of the file itself were last modified.
	ModTime() time.Time
	// GetEmbeddedData returns the raw byte data if the file content is embedded directly in the metadata.
	// It returns nil if the content is not embedded.
	GetEmbeddedData() []byte
	// GetShards returns a list of blob hashes if the file content is stored in external blobs (shards).
	// It returns nil if the content is embedded or the file is empty.
	GetShards() []string
}

type FileMetaVersion struct {
	Version int32 `msgpack:"v"`
}

type Store interface {
	// Create persists a new FileMeta object using a pre-determined, content-derived ID.
	// The caller is responsible for generating the correct ID.
	Create(id string, fileMeta FileMeta) error
	// Get retrieves a FileMeta object by its ID. It must handle different versions for backward compatibility.
	Get(id string) (FileMeta, error)
	// Exists checks if a FileMeta object with the given ID exists.
	Exists(id string) (bool, error)
	// Update overwrites an existing FileMeta object.
	Update(id string, fileMeta FileMeta) (FileMeta, error)
	// Delete removes a FileMeta object by its ID.
	Delete(id string) error
	// Migrate migrates a FileMeta object from a previous version to the current version.
	Migrate(id string) (FileMeta, error)
	// CurrentVersion returns the version number used for writing new metadata.
	CurrentVersion() int
}

type StoreMeta[T FileMeta] struct {
	Version int32 `json:"version" msgpack:"v"`
	Data    T     `json:"data" msgpack:"d"`
}