import { envNumber } from "./env.ts";

const limitEnv = envNumber("LUME_CONCURRENCY");
const limitDefault = limitEnv !== undefined && limitEnv >= 1 ? limitEnv : 200;

/** Run a callback concurrently with all the elements of an Iterable */
export async function concurrent<Type>(
  iterable: AsyncIterable<Type> | Iterable<Type>,
  iteratorFn: (arg: Type) => Promise<unknown>,
  limit = limitDefault,
) {
  const executing: Promise<unknown>[] = [];

  for await (const item of iterable) {
    const p: Promise<unknown> = iteratorFn(item).then(() =>
      executing.splice(executing.indexOf(p), 1)
    );

    executing.push(p);

    if (executing.length >= limit) {
      await Promise.race(executing);
    }
  }

  await Promise.all(executing);
}