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