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.maybe;

import java.util.concurrent.Callable;

import io.reactivex.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.internal.disposables.EmptyDisposable;
import io.reactivex.internal.functions.ObjectHelper;

Defers the creation of the actual Maybe the incoming MaybeObserver is subscribed to.
Type parameters:
<T> – the value type/**
 * Defers the creation of the actual Maybe the incoming MaybeObserver is subscribed to.
 *
 * @param <T> the value type
 */
public final class MaybeDefer<T> extends Maybe<T> {

    final Callable<? extends MaybeSource<? extends T>> maybeSupplier;

    public MaybeDefer(Callable<? extends MaybeSource<? extends T>> maybeSupplier) {
        this.maybeSupplier = maybeSupplier;
    }

    @Override
    protected void subscribeActual(MaybeObserver<? super T> observer) {
        MaybeSource<? extends T> source;

        try {
            source = ObjectHelper.requireNonNull(maybeSupplier.call(), "The maybeSupplier returned a null MaybeSource");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptyDisposable.error(ex, observer);
            return;
        }

        source.subscribe(observer);
    }
}