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 java.util.concurrent.atomic.AtomicReference;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.*;
import io.reactivex.functions.*;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.plugins.RxJavaPlugins;

Creates a resource and a dependent Maybe for each incoming Observer and optionally
disposes the resource eagerly (before the terminal event is send out).
Type parameters:
<T> – the value type
<D> – the resource type/**
 * Creates a resource and a dependent Maybe for each incoming Observer and optionally
 * disposes the resource eagerly (before the terminal event is send out).
 *
 * @param <T> the value type
 * @param <D> the resource type
 */
public final class MaybeUsing<T, D> extends Maybe<T> {

    final Callable<? extends D> resourceSupplier;

    final Function<? super D, ? extends MaybeSource<? extends T>> sourceSupplier;

    final Consumer<? super D> resourceDisposer;

    final boolean eager;

    public MaybeUsing(Callable<? extends D> resourceSupplier,
            Function<? super D, ? extends MaybeSource<? extends T>> sourceSupplier,
            Consumer<? super D> resourceDisposer,
            boolean eager) {
        this.resourceSupplier = resourceSupplier;
        this.sourceSupplier = sourceSupplier;
        this.resourceDisposer = resourceDisposer;
        this.eager = eager;
    }

    @Override
    protected void subscribeActual(MaybeObserver<? super T> observer) {
        D resource;

        try {
            resource = resourceSupplier.call();
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptyDisposable.error(ex, observer);
            return;
        }

        MaybeSource<? extends T> source;

        try {
            source = ObjectHelper.requireNonNull(sourceSupplier.apply(resource), "The sourceSupplier returned a null MaybeSource");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            if (eager) {
                try {
                    resourceDisposer.accept(resource);
                } catch (Throwable exc) {
                    Exceptions.throwIfFatal(exc);
                    EmptyDisposable.error(new CompositeException(ex, exc), observer);
                    return;
                }
            }

            EmptyDisposable.error(ex, observer);

            if (!eager) {
                try {
                    resourceDisposer.accept(resource);
                } catch (Throwable exc) {
                    Exceptions.throwIfFatal(exc);
                    RxJavaPlugins.onError(exc);
                }
            }
            return;
        }

        source.subscribe(new UsingObserver<T, D>(observer, resource, resourceDisposer, eager));
    }

    static final class UsingObserver<T, D>
    extends AtomicReference<Object>
    implements MaybeObserver<T>, Disposable {

        private static final long serialVersionUID = -674404550052917487L;

        final MaybeObserver<? super T> downstream;

        final Consumer<? super D> disposer;

        final boolean eager;

        Disposable upstream;

        UsingObserver(MaybeObserver<? super T> actual, D resource, Consumer<? super D> disposer, boolean eager) {
            super(resource);
            this.downstream = actual;
            this.disposer = disposer;
            this.eager = eager;
        }

        @Override
        public void dispose() {
            upstream.dispose();
            upstream = DisposableHelper.DISPOSED;
            disposeResourceAfter();
        }

        @SuppressWarnings("unchecked")
        void disposeResourceAfter() {
            Object resource = getAndSet(this);
            if (resource != this) {
                try {
                    disposer.accept((D)resource);
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    RxJavaPlugins.onError(ex);
                }
            }
        }

        @Override
        public boolean isDisposed() {
            return upstream.isDisposed();
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.validate(this.upstream, d)) {
                this.upstream = d;

                downstream.onSubscribe(this);
            }
        }

        @SuppressWarnings("unchecked")
        @Override
        public void onSuccess(T value) {
            upstream = DisposableHelper.DISPOSED;
            if (eager) {
                Object resource = getAndSet(this);
                if (resource != this) {
                    try {
                        disposer.accept((D)resource);
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        downstream.onError(ex);
                        return;
                    }
                } else {
                    return;
                }
            }

            downstream.onSuccess(value);

            if (!eager) {
                disposeResourceAfter();
            }
        }

        @SuppressWarnings("unchecked")
        @Override
        public void onError(Throwable e) {
            upstream = DisposableHelper.DISPOSED;
            if (eager) {
                Object resource = getAndSet(this);
                if (resource != this) {
                    try {
                        disposer.accept((D)resource);
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        e = new CompositeException(e, ex);
                    }
                } else {
                    return;
                }
            }

            downstream.onError(e);

            if (!eager) {
                disposeResourceAfter();
            }
        }

        @SuppressWarnings("unchecked")
        @Override
        public void onComplete() {
            upstream = DisposableHelper.DISPOSED;
            if (eager) {
                Object resource = getAndSet(this);
                if (resource != this) {
                    try {
                        disposer.accept((D)resource);
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        downstream.onError(ex);
                        return;
                    }
                } else {
                    return;
                }
            }

            downstream.onComplete();

            if (!eager) {
                disposeResourceAfter();
            }
        }
    }
}