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.flowable;

import java.util.concurrent.Callable;

import org.reactivestreams.*;

import io.reactivex.Flowable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.plugins.RxJavaPlugins;

Utility classes to work with scalar-sourced XMap operators (where X == { flat, concat, switch }).
/**
 * Utility classes to work with scalar-sourced XMap operators (where X == { flat, concat, switch }).
 */
public final class FlowableScalarXMap {

    
Utility class. /** Utility class. */
    private FlowableScalarXMap() {
        throw new IllegalStateException("No instances!");
    }

    
Tries to subscribe to a possibly Callable source's mapped Publisher.
Params:
source – the source Publisher
subscriber – the subscriber
mapper – the function mapping a scalar value into a Publisher
Type parameters:
<T> – the input value type
<R> – the output value type
Returns:
true if successful, false if the caller should continue with the regular path./**
     * Tries to subscribe to a possibly Callable source's mapped Publisher.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param source the source Publisher
     * @param subscriber the subscriber
     * @param mapper the function mapping a scalar value into a Publisher
     * @return true if successful, false if the caller should continue with the regular path.
     */
    @SuppressWarnings("unchecked")
    public static <T, R> boolean tryScalarXMapSubscribe(Publisher<T> source,
            Subscriber<? super R> subscriber,
            Function<? super T, ? extends Publisher<? extends R>> mapper) {
        if (source instanceof Callable) {
            T t;

            try {
                t = ((Callable<T>)source).call();
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptySubscription.error(ex, subscriber);
                return true;
            }

            if (t == null) {
                EmptySubscription.complete(subscriber);
                return true;
            }

            Publisher<? extends R> r;

            try {
                r = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null Publisher");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                EmptySubscription.error(ex, subscriber);
                return true;
            }

            if (r instanceof Callable) {
                R u;

                try {
                    u = ((Callable<R>)r).call();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    EmptySubscription.error(ex, subscriber);
                    return true;
                }

                if (u == null) {
                    EmptySubscription.complete(subscriber);
                    return true;
                }
                subscriber.onSubscribe(new ScalarSubscription<R>(subscriber, u));
            } else {
                r.subscribe(subscriber);
            }

            return true;
        }
        return false;
    }

    
Maps a scalar value into a Publisher and emits its values.
Params:
value – the scalar value to map
mapper – the function that gets the scalar value and should return
a Publisher that gets streamed
Type parameters:
<T> – the scalar value type
<U> – the output value type
Returns:
the new Flowable instance/**
     * Maps a scalar value into a Publisher and emits its values.
     *
     * @param <T> the scalar value type
     * @param <U> the output value type
     * @param value the scalar value to map
     * @param mapper the function that gets the scalar value and should return
     * a Publisher that gets streamed
     * @return the new Flowable instance
     */
    public static <T, U> Flowable<U> scalarXMap(final T value, final Function<? super T, ? extends Publisher<? extends U>> mapper) {
        return RxJavaPlugins.onAssembly(new ScalarXMapFlowable<T, U>(value, mapper));
    }

    
Maps a scalar value to a Publisher and subscribes to it.
Type parameters:
<T> – the scalar value type
<R> – the mapped Publisher's element type./**
     * Maps a scalar value to a Publisher and subscribes to it.
     *
     * @param <T> the scalar value type
     * @param <R> the mapped Publisher's element type.
     */
    static final class ScalarXMapFlowable<T, R> extends Flowable<R> {

        final T value;

        final Function<? super T, ? extends Publisher<? extends R>> mapper;

        ScalarXMapFlowable(T value,
                Function<? super T, ? extends Publisher<? extends R>> mapper) {
            this.value = value;
            this.mapper = mapper;
        }

        @SuppressWarnings("unchecked")
        @Override
        public void subscribeActual(Subscriber<? super R> s) {
            Publisher<? extends R> other;
            try {
                other = ObjectHelper.requireNonNull(mapper.apply(value), "The mapper returned a null Publisher");
            } catch (Throwable e) {
                EmptySubscription.error(e, s);
                return;
            }
            if (other instanceof Callable) {
                R u;

                try {
                    u = ((Callable<R>)other).call();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    EmptySubscription.error(ex, s);
                    return;
                }

                if (u == null) {
                    EmptySubscription.complete(s);
                    return;
                }
                s.onSubscribe(new ScalarSubscription<R>(s, u));
            } else {
                other.subscribe(s);
            }
        }
    }
}