/**
 * Async input queue — copy of the helper from `harnesses/claude.ts:37-68`.
 *
 * The Claude harness uses this exact shape as the input prompt to the Claude
 * Agent SDK's long-lived `query()`. The pi session loop uses the same pattern
 * so the non-blocking live-conversation behavior matches Claude byte-for-byte
 * at the queue level: pushMessage() never awaits the model, and each queued
 * message is consumed as its own turn.
 *
 * Deliberately NO bulk-drain helper: an earlier `drainPending()` let the
 * session fold mid-turn messages into the in-flight turn, which broke the
 * channel manager's one-routing-target-per-push FIFO (see
 * PI-PARITY-AUDIT-2026-06-11.md D1-1). One message in → one turn out.
 */
export interface AsyncQueue<T> extends AsyncIterable<T> {
  push(item: T): void;
  end(): void;
}

export function createAsyncQueue<T>(): AsyncQueue<T> {
  const pending: T[] = [];
  let resolve: ((value: IteratorResult<T>) => void) | null = null;
  let done = false;

  return {
    push(item: T) {
      if (done) return;
      if (resolve) {
        resolve({ value: item, done: false });
        resolve = null;
      } else {
        pending.push(item);
      }
    },
    end() {
      done = true;
      if (resolve) resolve({ value: undefined as any, done: true });
    },
    [Symbol.asyncIterator]() {
      return {
        next(): Promise<IteratorResult<T>> {
          if (pending.length > 0) {
            return Promise.resolve({ value: pending.shift()!, done: false });
          }
          if (done) return Promise.resolve({ value: undefined as any, done: true });
          return new Promise((r) => { resolve = r; });
        },
      };
    },
  };
}