Chris@0: <?php
Chris@0: namespace GuzzleHttp\Promise;
Chris@0: 
Chris@0: /**
Chris@0:  * Promises/A+ implementation that avoids recursion when possible.
Chris@0:  *
Chris@0:  * @link https://promisesaplus.com/
Chris@0:  */
Chris@0: class Promise implements PromiseInterface
Chris@0: {
Chris@0:     private $state = self::PENDING;
Chris@0:     private $result;
Chris@0:     private $cancelFn;
Chris@0:     private $waitFn;
Chris@0:     private $waitList;
Chris@0:     private $handlers = [];
Chris@0: 
Chris@0:     /**
Chris@0:      * @param callable $waitFn   Fn that when invoked resolves the promise.
Chris@0:      * @param callable $cancelFn Fn that when invoked cancels the promise.
Chris@0:      */
Chris@0:     public function __construct(
Chris@0:         callable $waitFn = null,
Chris@0:         callable $cancelFn = null
Chris@0:     ) {
Chris@0:         $this->waitFn = $waitFn;
Chris@0:         $this->cancelFn = $cancelFn;
Chris@0:     }
Chris@0: 
Chris@0:     public function then(
Chris@0:         callable $onFulfilled = null,
Chris@0:         callable $onRejected = null
Chris@0:     ) {
Chris@0:         if ($this->state === self::PENDING) {
Chris@0:             $p = new Promise(null, [$this, 'cancel']);
Chris@0:             $this->handlers[] = [$p, $onFulfilled, $onRejected];
Chris@0:             $p->waitList = $this->waitList;
Chris@0:             $p->waitList[] = $this;
Chris@0:             return $p;
Chris@0:         }
Chris@0: 
Chris@0:         // Return a fulfilled promise and immediately invoke any callbacks.
Chris@0:         if ($this->state === self::FULFILLED) {
Chris@0:             return $onFulfilled
Chris@0:                 ? promise_for($this->result)->then($onFulfilled)
Chris@0:                 : promise_for($this->result);
Chris@0:         }
Chris@0: 
Chris@0:         // It's either cancelled or rejected, so return a rejected promise
Chris@0:         // and immediately invoke any callbacks.
Chris@0:         $rejection = rejection_for($this->result);
Chris@0:         return $onRejected ? $rejection->then(null, $onRejected) : $rejection;
Chris@0:     }
Chris@0: 
Chris@0:     public function otherwise(callable $onRejected)
Chris@0:     {
Chris@0:         return $this->then(null, $onRejected);
Chris@0:     }
Chris@0: 
Chris@0:     public function wait($unwrap = true)
Chris@0:     {
Chris@0:         $this->waitIfPending();
Chris@0: 
Chris@0:         $inner = $this->result instanceof PromiseInterface
Chris@0:             ? $this->result->wait($unwrap)
Chris@0:             : $this->result;
Chris@0: 
Chris@0:         if ($unwrap) {
Chris@0:             if ($this->result instanceof PromiseInterface
Chris@0:                 || $this->state === self::FULFILLED
Chris@0:             ) {
Chris@0:                 return $inner;
Chris@0:             } else {
Chris@0:                 // It's rejected so "unwrap" and throw an exception.
Chris@0:                 throw exception_for($inner);
Chris@0:             }
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     public function getState()
Chris@0:     {
Chris@0:         return $this->state;
Chris@0:     }
Chris@0: 
Chris@0:     public function cancel()
Chris@0:     {
Chris@0:         if ($this->state !== self::PENDING) {
Chris@0:             return;
Chris@0:         }
Chris@0: 
Chris@0:         $this->waitFn = $this->waitList = null;
Chris@0: 
Chris@0:         if ($this->cancelFn) {
Chris@0:             $fn = $this->cancelFn;
Chris@0:             $this->cancelFn = null;
Chris@0:             try {
Chris@0:                 $fn();
Chris@0:             } catch (\Throwable $e) {
Chris@0:                 $this->reject($e);
Chris@0:             } catch (\Exception $e) {
Chris@0:                 $this->reject($e);
Chris@0:             }
Chris@0:         }
Chris@0: 
Chris@0:         // Reject the promise only if it wasn't rejected in a then callback.
Chris@0:         if ($this->state === self::PENDING) {
Chris@0:             $this->reject(new CancellationException('Promise has been cancelled'));
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     public function resolve($value)
Chris@0:     {
Chris@0:         $this->settle(self::FULFILLED, $value);
Chris@0:     }
Chris@0: 
Chris@0:     public function reject($reason)
Chris@0:     {
Chris@0:         $this->settle(self::REJECTED, $reason);
Chris@0:     }
Chris@0: 
Chris@0:     private function settle($state, $value)
Chris@0:     {
Chris@0:         if ($this->state !== self::PENDING) {
Chris@0:             // Ignore calls with the same resolution.
Chris@0:             if ($state === $this->state && $value === $this->result) {
Chris@0:                 return;
Chris@0:             }
Chris@0:             throw $this->state === $state
Chris@0:                 ? new \LogicException("The promise is already {$state}.")
Chris@0:                 : new \LogicException("Cannot change a {$this->state} promise to {$state}");
Chris@0:         }
Chris@0: 
Chris@0:         if ($value === $this) {
Chris@0:             throw new \LogicException('Cannot fulfill or reject a promise with itself');
Chris@0:         }
Chris@0: 
Chris@0:         // Clear out the state of the promise but stash the handlers.
Chris@0:         $this->state = $state;
Chris@0:         $this->result = $value;
Chris@0:         $handlers = $this->handlers;
Chris@0:         $this->handlers = null;
Chris@0:         $this->waitList = $this->waitFn = null;
Chris@0:         $this->cancelFn = null;
Chris@0: 
Chris@0:         if (!$handlers) {
Chris@0:             return;
Chris@0:         }
Chris@0: 
Chris@0:         // If the value was not a settled promise or a thenable, then resolve
Chris@0:         // it in the task queue using the correct ID.
Chris@0:         if (!method_exists($value, 'then')) {
Chris@0:             $id = $state === self::FULFILLED ? 1 : 2;
Chris@0:             // It's a success, so resolve the handlers in the queue.
Chris@0:             queue()->add(static function () use ($id, $value, $handlers) {
Chris@0:                 foreach ($handlers as $handler) {
Chris@0:                     self::callHandler($id, $value, $handler);
Chris@0:                 }
Chris@0:             });
Chris@0:         } elseif ($value instanceof Promise
Chris@0:             && $value->getState() === self::PENDING
Chris@0:         ) {
Chris@0:             // We can just merge our handlers onto the next promise.
Chris@0:             $value->handlers = array_merge($value->handlers, $handlers);
Chris@0:         } else {
Chris@0:             // Resolve the handlers when the forwarded promise is resolved.
Chris@0:             $value->then(
Chris@0:                 static function ($value) use ($handlers) {
Chris@0:                     foreach ($handlers as $handler) {
Chris@0:                         self::callHandler(1, $value, $handler);
Chris@0:                     }
Chris@0:                 },
Chris@0:                 static function ($reason) use ($handlers) {
Chris@0:                     foreach ($handlers as $handler) {
Chris@0:                         self::callHandler(2, $reason, $handler);
Chris@0:                     }
Chris@0:                 }
Chris@0:             );
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     /**
Chris@0:      * Call a stack of handlers using a specific callback index and value.
Chris@0:      *
Chris@0:      * @param int   $index   1 (resolve) or 2 (reject).
Chris@0:      * @param mixed $value   Value to pass to the callback.
Chris@0:      * @param array $handler Array of handler data (promise and callbacks).
Chris@0:      *
Chris@0:      * @return array Returns the next group to resolve.
Chris@0:      */
Chris@0:     private static function callHandler($index, $value, array $handler)
Chris@0:     {
Chris@0:         /** @var PromiseInterface $promise */
Chris@0:         $promise = $handler[0];
Chris@0: 
Chris@0:         // The promise may have been cancelled or resolved before placing
Chris@0:         // this thunk in the queue.
Chris@0:         if ($promise->getState() !== self::PENDING) {
Chris@0:             return;
Chris@0:         }
Chris@0: 
Chris@0:         try {
Chris@0:             if (isset($handler[$index])) {
Chris@0:                 $promise->resolve($handler[$index]($value));
Chris@0:             } elseif ($index === 1) {
Chris@0:                 // Forward resolution values as-is.
Chris@0:                 $promise->resolve($value);
Chris@0:             } else {
Chris@0:                 // Forward rejections down the chain.
Chris@0:                 $promise->reject($value);
Chris@0:             }
Chris@0:         } catch (\Throwable $reason) {
Chris@0:             $promise->reject($reason);
Chris@0:         } catch (\Exception $reason) {
Chris@0:             $promise->reject($reason);
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     private function waitIfPending()
Chris@0:     {
Chris@0:         if ($this->state !== self::PENDING) {
Chris@0:             return;
Chris@0:         } elseif ($this->waitFn) {
Chris@0:             $this->invokeWaitFn();
Chris@0:         } elseif ($this->waitList) {
Chris@0:             $this->invokeWaitList();
Chris@0:         } else {
Chris@0:             // If there's not wait function, then reject the promise.
Chris@0:             $this->reject('Cannot wait on a promise that has '
Chris@0:                 . 'no internal wait function. You must provide a wait '
Chris@0:                 . 'function when constructing the promise to be able to '
Chris@0:                 . 'wait on a promise.');
Chris@0:         }
Chris@0: 
Chris@0:         queue()->run();
Chris@0: 
Chris@0:         if ($this->state === self::PENDING) {
Chris@0:             $this->reject('Invoking the wait callback did not resolve the promise');
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     private function invokeWaitFn()
Chris@0:     {
Chris@0:         try {
Chris@0:             $wfn = $this->waitFn;
Chris@0:             $this->waitFn = null;
Chris@0:             $wfn(true);
Chris@0:         } catch (\Exception $reason) {
Chris@0:             if ($this->state === self::PENDING) {
Chris@0:                 // The promise has not been resolved yet, so reject the promise
Chris@0:                 // with the exception.
Chris@0:                 $this->reject($reason);
Chris@0:             } else {
Chris@0:                 // The promise was already resolved, so there's a problem in
Chris@0:                 // the application.
Chris@0:                 throw $reason;
Chris@0:             }
Chris@0:         }
Chris@0:     }
Chris@0: 
Chris@0:     private function invokeWaitList()
Chris@0:     {
Chris@0:         $waitList = $this->waitList;
Chris@0:         $this->waitList = null;
Chris@0: 
Chris@0:         foreach ($waitList as $result) {
Chris@0:             while (true) {
Chris@0:                 $result->waitIfPending();
Chris@0: 
Chris@0:                 if ($result->result instanceof Promise) {
Chris@0:                     $result = $result->result;
Chris@0:                 } else {
Chris@0:                     if ($result->result instanceof PromiseInterface) {
Chris@0:                         $result->result->wait(false);
Chris@0:                     }
Chris@0:                     break;
Chris@0:                 }
Chris@0:             }
Chris@0:         }
Chris@0:     }
Chris@0: }