novy-syndicate/actor.ts

import { Value } from 'preserves';

type Assertion = Value<Peer>;

type ActorId = number;

type ExitReason = null | { ok: true } | { ok: false, err: Error };

let nextActorId: ActorId = 0;

type AssertionHandle = object;

const assert = Symbol('assert');
const retract = Symbol('retract');
const message = Symbol('message');

type RestParameters<T extends (arg: any, ...args: any) => any> =
    T extends (arg: any, ...args: infer P) => any ? P : never;

type Event =
    | { type: typeof assert, args: RestParameters<Facet[typeof assert]> }
    | { type: typeof retract, args: RestParameters<Facet[typeof retract]> }
    | { type: typeof message, args: RestParameters<Facet[typeof message]> }

type Action = Event;

class Peer {
    readonly actor: Actor;
    readonly target: Facet;

    constructor(actor: Actor, target: Facet) {
        this.actor = actor;
        this.target = target;
    }
}

interface Facet {
    [assert](turn: Turn, assertion: Assertion, handle: AssertionHandle): void;
    [retract](turn: Turn, handle: AssertionHandle): void;
    [message](turn: Turn, message: Assertion): void;
}

class Actor {
    readonly id: ActorId = nextActorId++;
    exitReason: ExitReason = null;

    scheduleTurn(target: Facet, turn: Turn) {
        queueMicrotask(() => {
            if (this.alive) {
                try {
                    const event = turn.event;
                    (target as any)[event.type](turn, ...event.args);
                    // ^ This is safe. Try replacing it with the following to see:
                    //
                    // switch (event.type) {
                    //     case assert:  target[event.type](turn, ...event.args); break;
                    //     case retract: target[event.type](turn, ...event.args); break;
                    //     case message: target[event.type](turn, ...event.args); break;
                    // }
                    turn.finish();
                } catch (err) {
                    this.terminateWith({ ok: false, err });
                }
            }
        });
    }

    get alive(): boolean {
        return this.exitReason === null;
    }

    stop() {
        this.terminateWith({ ok: true });
    }

    terminateWith(reason: Exclude<ExitReason, null>) {
        if (this.alive) {
            this.exitReason = reason;
            // TODO cleanup
        }
    }
}

class Turn {
    readonly recipient: Actor;
    readonly event: Event;
    readonly actions: Map<Actor, Map<Facet, Action[]>> = new Map();

    constructor(recipient: Actor, event: Event) {
        this.recipient = recipient;
        this.event = event;
    }

    enqueueAction(peer: Peer, action: Action) {
        let targetMap = this.actions.get(peer.actor);
        if (targetMap === void 0) {
            targetMap = new Map();
            this.actions.set(peer.actor, targetMap);
        }
        let actions = targetMap.get(peer.target);
        if (actions === void 0) {
            actions = [];
            targetMap.set(peer.target, actions);
        }
        actions.push(action);
    }

    finish() {
        this.actions.forEach((targetMap, actor) => {
            targetMap.forEach((actions, target) => {
                actions.forEach(action => actor.scheduleTurn(target, new Turn(actor, action)));
            });
        });
    }
}