Paradox 3.0

EventSourceReducer.ts

// Demonstration of Core Concepts
// Event Source Reducer functional style and typesafe

// ========================= 
//  Lib Event Source 
// =========================

type UserDocument = object

type State = ReadonlyArray<object>

interface UserEvent<TDocument extends UserDocument> {
    readonly kind: EventKind
    readonly document: Partial<TDocument>
}

type EventReducer<
        TDocument extends UserDocument,
        TEvent extends UserEvent<TDocument>
    > = (
        document: TDocument,
        event: TEvent
    ) =>
        TDocument

const EventReducer = <
        TDocument extends UserDocument,
        TEvent extends UserEvent<TDocument>
    >(
        document: TDocument,
        event: TEvent
    ) =>
        ({ ...document, ...event.document })
  

// ========================= 
//  Client-Code
// ========================= 
  

// import { UserDocument, UserEvent, EventReducer } from './event_source'

// documents

interface Person extends UserDocument {
    name: string
    age: number
}

interface Address {
    street: string
    zipCode: number
}


// events

type ChangePersonName = (newName: string) => UserEvent<Person>
type ChangeAddressZipCode = (zipCode: number) => UserEvent<Address>


// -- implementation ---

const ChangePersonName: ChangePersonName =
    name => ({
        kind: "ChangePersonName",
        document: { name }
    })

const ChangeAddressZipCode: ChangeAddressZipCode =
    zipCode => ({
        kind: "ChangeAddressZipCode",
        document: { zipCode }
    }) 

// test - Generate Events

const initialPerson: Person = {
    name: "Gustavo",
    age: 666
}

const initialAddress: Address = {
    street: "R. Roz",
    zipCode: 7
}


// test

// ok -> no Error
const newPersonState = EventReducer(initialPerson,ChangePersonName("Flavio"))
// ok -> Error = imcompatible parameters
const newPersonState2 = EventReducer(initialAddress, ChangePersonName("Flavio"))