<?php
namespace GuzzleHttp\Promise;
use Exception;
use Generator;
use Throwable;
/**
* Creates a promise that is resolved using a generator that yields values or
* promises (somewhat similar to C#'s async keyword).
*
* When called, the Coroutine::of method will start an instance of the generator
* and returns a promise that is fulfilled with its final yielded value.
*
* Control is returned back to the generator when the yielded promise settles.
* This can lead to less verbose code when doing lots of sequential async calls
* with minimal processing in between.
*
* use GuzzleHttp\Promise;
*
* function createPromise($value) {
* return new Promise\FulfilledPromise($value);
* }
*
* $promise = Promise\Coroutine::of(function () {
* $value = (yield createPromise('a'));
* try {
* $value = (yield createPromise($value . 'b'));
* } catch (\Exception $e) {
* // The promise was rejected.
* }
* yield $value . 'c';
* });
*
* // Outputs "abc"
* $promise->then(function ($v) { echo $v; });
*
* @param callable $generatorFn Generator function to wrap into a promise.
*
* @return Promise
*
* @link https://github.com/petkaantonov/bluebird/blob/master/API.md#generators inspiration
*/
final class Coroutine implements PromiseInterface
{
/**
* @var PromiseInterface|null
*/
private $currentPromise;
/**
* @var Generator
*/
private $generator;
/**
* @var Promise
*/
private $result;
public function __construct(callable $generatorFn)
{
$this->generator = $generatorFn();
$this->result = new Promise(function () {
while (isset($this->currentPromise)) {
$this->currentPromise->wait();
}
});
try {
$this->nextCoroutine($this->generator->current());
} catch (\Exception $exception) {
$this->result->reject($exception);
} catch (Throwable $throwable) {
$this->result->reject($throwable);
}
}
/**
* Create a new coroutine.
*
* @return self
*/
public static function of(callable $generatorFn)
{
return new self($generatorFn);
}
public function then(
callable $onFulfilled = null,
callable $onRejected = null
) {
return $this->result->then($onFulfilled, $onRejected);
}
public function otherwise(callable $onRejected)
{
return $this->result->otherwise($onRejected);
}
public function wait($unwrap = true)
{
return $this->result->wait($unwrap);
}
public function getState()
{
return $this->result->getState();
}
public function resolve($value)
{
$this->result->resolve($value);
}
public function reject($reason)
{
$this->result->reject($reason);
}
public function cancel()
{
$this->currentPromise->cancel();
$this->result->cancel();
}
private function nextCoroutine($yielded)
{
$this->currentPromise = Create::promiseFor($yielded)
->then([$this, '_handleSuccess'], [$this, '_handleFailure']);
}
/**
* @internal
*/
public function _handleSuccess($value)
{
unset($this->currentPromise);
try {
$next = $this->generator->send($value);
if ($this->generator->valid()) {
$this->nextCoroutine($next);
} else {
$this->result->resolve($value);
}
} catch (Exception $exception) {
$this->result->reject($exception);
} catch (Throwable $throwable) {
$this->result->reject($throwable);
}
}
/**
* @internal
*/
public function _handleFailure($reason)
{
unset($this->currentPromise);
try {
$nextYield = $this->generator->throw(Create::exceptionFor($reason));
// The throw was caught, so keep iterating on the coroutine
$this->nextCoroutine($nextYield);
} catch (Exception $exception) {
$this->result->reject($exception);
} catch (Throwable $throwable) {
$this->result->reject($throwable);
}
}
}