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import { Channel, Receiver, Sender } from "./channel.ts";import { UnreachableError } from "./internal/errors.ts";import { isReceiver, isSender, sleep } from "./internal/utils.ts";
/** * Extra options used for the `select` function. */export interface SelectOptions<TDefault = never> {  default: TDefault;  abortCtrl?: AbortController;}
export type SelectGetOperation<T> = Receiver<T>;export type SelectSendOperation<T> = [Sender<T>, T];
export type SelectOperation<T> =  | SelectGetOperation<T>  | SelectSendOperation<T>;export type SelectDefaultResult<T> = [T, undefined];export type SelectOperationResult<T> =  | [T, Receiver<T>]  | [true, Sender<T>];export type SelectResult<T, TDefault> = (  | SelectOperationResult<T>  | SelectDefaultResult<TDefault>);
export function isSelectSendOperation(  x: unknown,): x is SelectSendOperation<unknown> {  return Array.isArray(x) && x.length === 2 && isSender(x[0]);}
export function isSelectOperation(x: unknown): x is SelectOperation<unknown> {  return isReceiver(x) || isSelectSendOperation(x);}
export async function select(  ops: [],  options?:    | SelectOptions<never>    | Omit<SelectOptions<never>, "default">,): Promise<never>;
export async function select<T, TDefault = never>(  ops: [SelectOperation<T>],  options?:    | SelectOptions<TDefault>    | Omit<SelectOptions<TDefault>, "default">,): Promise<SelectResult<T, TDefault>>;
export async function select<T1, T2, TDefault = never>(  ops: [SelectOperation<T1>, SelectOperation<T2>],  options?:    | SelectOptions<TDefault>    | Omit<SelectOptions<TDefault>, "default">,): Promise<  | SelectOperationResult<T1>  | SelectOperationResult<T2>  | SelectDefaultResult<TDefault>>;export async function select<T, TDefault = never>(  ops: Exclude<SelectOperation<T>[], []>,  options?:    | SelectOptions<TDefault>    | Omit<SelectOptions<TDefault>, "default">,): Promise<SelectResult<T, TDefault>>;/** * `select` takes a list of channel operations, and completes **at-most** one of * them (the first operation that is ready). * * If the `default` option is provided, and no operation is immediately read, * then all the operations will be aborted and the default value is returned. * * @template T, TDefault * @param {(Receiver<T> | [Sender<T>, T])[]} ops *   A list of channel operations. *   Each item in this list can be either a receiver or a tuple of a sender and *   the value to send. * @param {SelectOptions<T> | Omit<SelectOptions<T>, "default">} options *   The options for `select`. *   *Note: `undefined` is considered a valid value for `default`, so if you *   want to wait for one of the operations, omit `default` from the options *   struct.* * * @return {Promise<[T, Receiver<T>] | [true, Sender<T>] | [TDefault, undefined]>} *   If default is provided and no operation was ready, then the tuple *   `[default, undefined]` is returned. * *   If a `get` operation is completed, then the tuple `[T, Receiver<T>]` *   is returned (where `T` is the value received, and `Receiver<T>` is the *   receiver channel that returned it). * *   If a `send` operation is completed, then the tuple `[true, Sender<T>]` is *   returned (where `Sender<T>` is the sender channel that we sent the value *   with). */export async function select<T, TDefault = never>(  ops: SelectOperation<T>[],  options?:    | SelectOptions<TDefault>    | Omit<SelectOptions<TDefault>, "default">,): Promise<SelectResult<T, TDefault>> {  if (ops.length < 1) {    throw new TypeError("cannot perform select on less than 1 operation");  }  const abortCtrl = options?.abortCtrl || new AbortController();  const selectPromises: Promise<void | T | undefined>[] = ops.map((item) => {    if (isReceiver(item)) {      return item.get(abortCtrl).then(([val]) => val);    }    return item[0].send(item[1], abortCtrl);  });
  if (options && "default" in options) {    sleep(0).then(() => abortCtrl.abort());  }
  const results = await Promise.allSettled([...selectPromises]);
  for (let i = 0; i < results.length; i++) {    const item = ops[i];    const result = results[i];    if (result.status === "rejected") continue;
    if (item instanceof Channel) {      return [result.value as T, item];    }
    if (Array.isArray(item)) {      return [true, item[0]];    }  }
  if (options && "default" in options) {    return [options.default, undefined];  }
  throw new UnreachableError();}