CacheEntry = object
  mid*: MessageId
  topicId*: string

MCache = object of RootObj
  msgs*: Table[MessageId, Message]
  history*: seq[seq[CacheEntry]]
  windowSize*: Natural

func contains(c: MCache; mid: MessageId): bool {....raises: [], tags: [].}

func get(c: MCache; mid: MessageId): Option[Message] {....raises: [], tags: [].}

func init(T: type MCache; window, history: Natural): T:type {....raises: [].}

func put(c: var MCache; msgId: MessageId; msg: Message) {....raises: [], tags: [].}

func shift(c: var MCache) {....raises: [], tags: [].}

func window(c: MCache; topic: string): HashSet[MessageId] {....raises: [], tags: [].}