import { availableParallelism } from 'node:os';

const MAX_LOCAL_WORKERS = 8;
const CPUS_PER_WORKER = 4;

// PM_TEST_WORKERS wins; CI without it keeps one worker, so CI only changes
// through explicit workflow edits; locally a quarter of the CPUs, at most eight.
export function workflowWorkers({ env = process.env, cpus = availableParallelism() } = {}) {
    if (env.PM_TEST_WORKERS !== undefined) {
        const workers = Number(env.PM_TEST_WORKERS);
        if (!Number.isInteger(workers) || workers < 1) {
            throw new Error(`PM_TEST_WORKERS must be a positive integer, got "${env.PM_TEST_WORKERS}"`);
        }
        return workers;
    }
    if (env.CI) return 1;
    return Math.max(1, Math.min(MAX_LOCAL_WORKERS, Math.floor(cpus / CPUS_PER_WORKER)));
}