Fraud Detector

fraud.ts

/*
Notes:

DataSource
  - a stream of data
    - hasNext(), getNext()
  - examples: Location, Transactions, Contacts, ...
  - an algorithm's output is a DataSource

Transaction
  - is a type of DataSource (stream)

Algorithm
  - takes a stream of data sources as input
  - outputs a stream of transactions with metadata
  - an algorithm output stream is a DataSource
  - can specify its data sources
*/
interface DataSource<T> {
  hasNext(): Boolean,
  getNext(): T
}

interface Algo<Out> {
  stream(): DataSource<Out>
}

class AppendLocationAlgo implements Algo<(Transaction, Location)> {
  ...
}

class AppendContactsAlgo implements Algo<(Transaction, Contact)> {
  ...
}

class SuspectFraudAlgo implements Algo<(Transaction, Boolean)> {
  ...
}

function getAlgo(id: AlgoId, sources: Map[DataSourceId, DataSource]): Algo {
  switch (id) {
    case Algo.AppendLocation:
      return AppendLocationAlgo({
        dependsOn: [],
        sources: [sources.locations, sources.transactions]
      })
    case Algo.AppendContacts:
      return new AppendContactsAlgo({
        dependsOn: [],
        sources: [sources.contacts, sources.transactions]
      })
    case Algo.SuspectFraud:
      return SuspectFraudAlgo({
        dependsOn: [Algo.AppendLocation, Algo.AppendContacts],
        sources: [sources.locations, sources.contacts, sources.transactions]
      })
    case default:
      throw new Error('invalid algoId specified')
  }  
}

class FraudDetector {
  private inputs: Map[DataSourceId, DataSource]
  private outputs: Map[AlgoId, DataSource]

  constructor(options: FraudDetectorOptions) {
    // entityId could correspond to a user, merchant, etc...
    // the data sources will vary depending on entity
    this.inputs = getDataSourceInputs(options.entityId) 
  }

  setAlgo(algoId: AlgoId): void {
    const algo = getAlgo(algoId, this.dataSources)
    this.outputs[algoId] = algo.stream()
  }

  removeAlgo(algo: AlgoId): void {
    // remove algo / cleanup
  }

  listen(algoId: AlgoId): DataSource {
    return this.outputs[algoId]
  }
}