import { fault } from '../canvas-core/values.ts';
import { createDeque } from './structures.ts';

/** Shared bounded transport capacity for writes, uploads and run reads. */
export function createNetworkGate(limit = 2) {
  if(!Number.isSafeInteger(limit)||limit<1)throw fault('invalid_concurrency');
  let active = 0;
  const waiting = createDeque<{ signal: AbortSignal; grant(): void; cancelled: boolean }>();
  async function enter(signal: AbortSignal) {
    signal.throwIfAborted();
    if (active < limit) { active++; return; }
    await new Promise<void>((resolve,reject) => {
      const item = { signal, cancelled: false, grant() { signal.removeEventListener('abort',abort);resolve(); } };
      const abort = () => { item.cancelled=true;signal.removeEventListener('abort',abort);reject(signal.reason); };
      signal.addEventListener('abort',abort,{once:true});waiting.push(item);
    });
  }
  function release() {
    let item=waiting.pop();while(item?.cancelled)item=waiting.pop();
    if(item)item.grant();else active--;
  }
  return Object.freeze({ async run<T>(signal: AbortSignal, callback: () => Promise<T>): Promise<T> {
    await enter(signal);
    try { signal.throwIfAborted();return await callback(); } finally { release(); }
  } });
}