machineGroupControl/src/dispatch/demandDispatcher.js

'use strict';

const { LatestWinsGate } = require('generalFunctions');

// Thin wrapper around LatestWinsGate for the MGC demand path. Replaces
// the original `_dispatchInFlight` + `_delayedCall` pair in
// specificClass.handleInput: a new demand arriving while a dispatch is
// in flight overwrites any pending one, so the latest value always wins
// and intermediates are dropped silently.

class DemandDispatcher {
    constructor(ctx = {}, runFn) {
        if (typeof runFn !== 'function') {
            throw new TypeError('DemandDispatcher requires a runFn');
        }
        this.ctx = ctx;
        this.logger = ctx.logger || null;
        this._runFn = runFn;
        this._gate = new LatestWinsGate(
            async (demand) => this._runFn(demand, this.ctx),
            { logger: this.logger },
        );
    }

    fire(demand) {
        this._gate.fire(demand);
    }

    // Returns a promise that resolves when THIS demand's dispatch settles.
    // If superseded by a later fireAndWait while parked, the promise
    // resolves with the LatestWinsGate SUPERSEDED sentinel
    // ({ superseded: true }) — callers can branch on it without try/catch.
    fireAndWait(demand) {
        return this._gate.fireAndWait(demand);
    }

    drain() {
        return this._gate.drain();
    }

    // Cancels any parked pending value so it cannot run. The currently
    // in-flight dispatch (if any) still runs to completion. A parked
    // fireAndWait promise resolves with the SUPERSEDED sentinel.
    cancelPending() {
        if (this._gate._pending) this._gate._supersedePending();
    }

    get inFlight() {
        return this._gate.size > 0;
    }
}

module.exports = DemandDispatcher;