Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.
/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.internal.operators.observable;

import java.util.concurrent.Callable;

import io.reactivex.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.observers.DeferredScalarDisposable;
import io.reactivex.plugins.RxJavaPlugins;

Calls a Callable and emits its resulting single value or signals its exception.
Type parameters:
<T> – the value type/**
 * Calls a Callable and emits its resulting single value or signals its exception.
 * @param <T> the value type
 */
public final class ObservableFromCallable<T> extends Observable<T> implements Callable<T> {
    final Callable<? extends T> callable;
    public ObservableFromCallable(Callable<? extends T> callable) {
        this.callable = callable;
    }

    @Override
    public void subscribeActual(Observer<? super T> observer) {
        DeferredScalarDisposable<T> d = new DeferredScalarDisposable<T>(observer);
        observer.onSubscribe(d);
        if (d.isDisposed()) {
            return;
        }
        T value;
        try {
            value = ObjectHelper.requireNonNull(callable.call(), "Callable returned null");
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            if (!d.isDisposed()) {
                observer.onError(e);
            } else {
                RxJavaPlugins.onError(e);
            }
            return;
        }
        d.complete(value);
    }

    @Override
    public T call() throws Exception {
        return ObjectHelper.requireNonNull(callable.call(), "The callable returned a null value");
    }
}