# Echo: Bunnymen Functional Spec

The user defines the following classes per datasource:

**Initializer** responsible for pulling the initial data when the node joins a
topic (optional).

interface Initializer{
  // This function contains custom logic for pulling data
  init() -> RawData
}

**Fetcher** responsible for pulling the latest data (required).

interface Fetcher{
  // This function contains custom logic for pulling latest data
  fetch() -> RawData
}

**Loader** responsible for implementing logic on how the data is stored. the
load() function could append, replace, or just keep the last 50 results from the
Fetcher.

interface Loader{
  // This function contains custom logic describing how the data is stored locally AND in ipfs
  load()
}

Once these classes are implemented, the user must register the dataset to
BunnymenDB.

bunnymenDB.registerDataset(key,Initializer, Fetcher, Loader, frequency)

Next, the user needs to define how the data from the dataset is processed. This
is defined in the TransformerFn.

transformerFn(rawData1, [rawData2], [rawData3], ...)->TransformedData -> {
  // custom logic that processes data from the dataset
}

The user can then register transformerFn as follows:

bunnymenDB.registerTransformer(key,transformerFn)

Finally, the user calls init to start the db

bunnymenDB.init()

BunnymenDB
  - registerDataset(key,...) // adds Datasets to key and node subscribes to key channel via Dataset
  - registerTransformer(key, transformFn) // adds transformFn to key
  - init() // starts node
  - get(key) -> TransformedData
      transformer = getTransformer(key)
      datasets = getDatsets(key)
      rawData1 = dataset[0].get()
      rawData2 = dataset[1].get()
      transformedData = transformFn(rawData1, rawData2)
      return transformedData

  // protected methods
  - getTransformer(key)
  - getDatasets(key)
  // protected members
  - Map<Key,Transformer> keytoTransformer
  - Map<Key,[Dataset]> keyToDatasets

Dataset
  - register( Initializer,
              Fetcher,
              Loader,
              frequency) // call Node.start(), Initializer.init(), Loader.load()
  - get() -> RawData // from ipfs or local cache
  - isStale() // marked stale if frequency+offset has passed
// protected members
  - Cache
  - Node
  - Initializer
  - Fetcher
  - Loader
  - currentCID

Node
  - Node(topic)
  - connect()
  - subscribe()
  - unsubscribe()
  - poll(frequency)
  - sendMessage()
  - uploadData()
  - downloadData()
  - selectLeader()
  // Events:
  - unSubscribe
  - subscribed
  - selectedLeader
  - sentMessage
  - receivedMessage
  - uploadedData
  - dowloadedData
  - peerSubscribed
  - peerUnsubscribed