lib/src/support/bus/StateEvent.ts

import {Container, Inject, Injectable, Instantiable} from '../../di'
import {Awaitable, ErrorWithContext, hasOwnProperty, JSONState, uuid4} from '../../util'
import {BaseSerializer} from './serial/BaseSerializer'
import {Event} from './types'

/**
 * An event base class that provides its own validator and serializer implementation.
 * This is meant to streamline event creation for app-space by forcing the payload of
 * the event to be a JSONState.
 */
@Injectable()
export abstract class StateEvent<T extends JSONState> implements Event {
    @Inject()
    protected readonly injector!: Container

    /** The payload of the event. */
    private state?: T

    eventUuid = uuid4()

    public get eventName(): string {
        return this.getName()
    }

    /** Validate the incoming data. */
    public abstract validate(state: JSONState): state is T

    /** Get the event's name for the bus. */
    public getName(): string {
        const ctor = this.constructor as typeof StateEvent
        return `state:${ctor.name}`
    }

    /** Get the Serializer implementation for this event. */
    public getSerializer(): StateEventSerializer {
        const ctor = this.constructor as typeof StateEvent
        return this.injector.makeNew<StateEventSerializer>(StateEventSerializer, ctor)
    }

    /** Validate & set the internal state of this event instance. */
    public setState(state: JSONState): this {
        if ( !this.validate(state) ) {
            throw new ErrorWithContext('Invalid state', {
                state,
            })
        }

        this.state = state
        return this
    }

    /** Get the internal state of this event, validated. */
    public getState(): T {
        if ( typeof this.state === 'undefined' ) {
            throw new ErrorWithContext('State has not been set on event')
        }

        return this.state
    }
}

/** A serialized `StateEvent` instance. */
export type SerializedStateEvent<T extends JSONState = JSONState> = {
    state: T,
    eventUuid: string,
}

export function isSerializedStateEvent(what: unknown): what is SerializedStateEvent {
    return (
        typeof what === 'object' && what !== null
        && hasOwnProperty(what, 'state')
        && hasOwnProperty(what, 'eventUuid')
        && typeof what.eventUuid === 'string'
    )
}

/**
 * Generic serializer implementation for StateEvents.
 * Note that this is NOT registered with @ObjectSerializer() because we need to
 * create an instance of this class for EACH implementation of StateEvent.
 * Still working that one out. For now, you'll need to manually register the
 * serializer. You can do this with the `getSerializer` method.
 *
 * @example
 * ```ts
 * type MyState = {
 *     id: number
 * }
 *
 * class MyStateEvent extends StateEvent<MyState> {
 *     public validate(state: JSONState): state is MyState {
 *         return is<MyState>(state)
 *     }
 * }
 * ```
 */
@Injectable()
export class StateEventSerializer extends BaseSerializer<StateEvent<JSONState>, SerializedStateEvent> {
    @Inject()
    protected readonly injector!: Container

    /** The StateEvent implementation. */
    public readonly eventClass: Instantiable<StateEvent<JSONState>>

    constructor(
        eventClass: Instantiable<StateEvent<JSONState>>,
    ) {
        super()
        this.eventClass = eventClass
    }

    matchActual(some: StateEvent<JSONState>): boolean {
        return some instanceof this.eventClass
    }

    protected encodeActual(actual: StateEvent<JSONState>): Awaitable<SerializedStateEvent> {
        return {
            state: actual.getState(),
            eventUuid: actual.eventUuid,
        }
    }

    protected decodeSerial(serial: SerializedStateEvent): Awaitable<StateEvent<JSONState>> {
        const inst = this.injector.makeNew<StateEvent<JSONState>>(this.eventClass)
        if ( !isSerializedStateEvent(serial) || !inst.validate(serial.state) ) {
            throw new ErrorWithContext('Invalid serial state', {
                serial,
                eventClass: inst.getName(),
            })
        }

        inst.setState(serial.state)
        inst.eventUuid = serial.eventUuid
        return inst
    }

    protected getName(): string {
        const inst = this.injector.makeNew<StateEvent<JSONState>>(this.eventClass)
        return `${inst.getName()}Serializer`
    }
}