storage

type CursorStorage interface {
	// GetCursorFor retrieves the given cursor.
	GetCursorFor(cursor *spec.Cursor) (*spec.Cursor, error)
	// SaveCursor persists the given cursor.
	SaveCursor(cursor *spec.Cursor) error
}

type EventStorage interface {
	// Append appends the given event to the log.
	Append(event *spec.Event) (*spec.Event, error)
	// GetIterator creates an iterator pointing to the given event.
	// EventsIterator.Value() will retrieves the given event.
	GetIterator(event *spec.Event) (EventsIterator, error)
}

type EventsIterator interface {
	io.Closer

	// Value returns the current event or nil if done.
	Value() (*spec.Event, error)

	// Next moves the iterator to the next event.
	// It returns false if the iterator is exhausted.
	Next() bool
}

type IDGenerator interface {
	// Next generates the next sortable and collision free event ID.
	Next() string
}

type KeyGenerator interface {
	// Cursor generates cursor key.
	Cursor(cursor *spec.Cursor) []byte
	// Event generates event key.
	Event(event *spec.Event) []byte
	// KeyToEvent reconstructs the event from the values in the given key (topic, id).
	KeyToEvent(key []byte) (*spec.Event, error)
}

type LevelDB interface {
	io.Closer
	Get(key []byte, ro *opt.ReadOptions) (value []byte, err error)
	Write(batch *leveldb.Batch, wo *opt.WriteOptions) error
	NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator
}

type Metrics interface {
	// MeasureAppendEvent measures duration and success rate of appending events
	MeasureAppendEvent(call func() (*spec.Event, error)) (*spec.Event, error)
	// MeasureGetIterator measures duration and success rate of iterator retrieval
	MeasureGetIterator(call func() (EventsIterator, error)) (EventsIterator, error)
}