<?php
namespace GuzzleHttp\Ring\Future;

use GuzzleHttp\Ring\Exception\CancelledFutureAccessException;
use GuzzleHttp\Ring\Exception\RingException;
use React\Promise\PromiseInterface;

/**
* Implements common future functionality built on top of promises.
*/
trait BaseFutureTrait
{
/** @var callable */
private $waitfn;

/** @var callable */
private $cancelfn;

/** @var PromiseInterface */
private $wrappedPromise;

/** @var \Exception Error encountered. */
private $error;

/** @var mixed Result of the future */
private $result;

private $isRealized = false;

/**
* @param PromiseInterface $promise Promise to shadow with the future.
* @param callable $wait Function that blocks until the deferred
* computation has been resolved. This
* function MUST resolve the deferred value
* associated with the supplied promise.
* @param callable $cancel If possible and reasonable, provide a
* function that can be used to cancel the
* future from completing.
*/
public function __construct(
PromiseInterface $promise,
callable $wait = null,
callable $cancel = null
) {
$this->wrappedPromise = $promise;
$this->waitfn = $wait;
$this->cancelfn = $cancel;
}

/**
* @return mixed
*/
public function wait()
{
if (!$this->isRealized) {
$this->addShadow();
if (!$this->isRealized && $this->waitfn) {
$this->invokeWait();
}
if (!$this->isRealized) {
$this->error = new RingException('Waiting did not resolve future');
}
}

if ($this->error) {
throw $this->error;
}

return $this->result;
}

/**
* @return PromiseInterface
*/
public function promise()
{
return $this->wrappedPromise;
}

/**
* @return PromiseInterface
*/
public function then(
callable $onFulfilled = null,
callable $onRejected = null,
callable $onProgress = null
) {
return $this->wrappedPromise->then($onFulfilled, $onRejected, $onProgress);
}

public function cancel()
{
if (!$this->isRealized) {
$cancelfn = $this->cancelfn;
$this->waitfn = $this->cancelfn = null;
$this->isRealized = true;
$this->error = new CancelledFutureAccessException();
if ($cancelfn) {
$cancelfn($this);
}
}
}

private function addShadow()
{
// Get the result and error when the promise is resolved. Note that
// calling this function might trigger the resolution immediately.
$this->wrappedPromise->then(
function ($value) {
$this->isRealized = true;
$this->result = $value;
$this->waitfn = $this->cancelfn = null;
},
function ($error) {
$this->isRealized = true;
$this->error = $error;
$this->waitfn = $this->cancelfn = null;
}
);
}

private function invokeWait()
{
try {
$wait = $this->waitfn;
$this->waitfn = null;
$wait();
} catch (\Exception $e) {
// Defer can throw to reject.
$this->error = $e;
$this->isRealized = true;
}
}
}