/**
* @param \Amp\Observable $observable
* @param callable(mixed $value): bool $filter
*
* @return \Amp\Observable
*/
function filter(Observable $observable, callable $filter) : Observable
{
$postponed = new Postponed();
$pending = true;
$observable->subscribe(function ($value) use(&$pending, $postponed, $filter) {
if ($pending) {
try {
if (!$filter($value)) {
return null;
}
return $postponed->emit($value);
} catch (\Throwable $exception) {
$pending = false;
$postponed->fail($exception);
}
}
return null;
});
$observable->when(function ($exception, $value) use(&$pending, $postponed) {
if (!$pending) {
return;
}
$pending = false;
if ($exception) {
$postponed->fail($exception);
return;
}
$postponed->resolve($value);
});
return $postponed->observe();
}