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.observers;

import io.reactivex.Observer;
import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.*;
import io.reactivex.internal.disposables.*;
import io.reactivex.plugins.RxJavaPlugins;

Wraps another Subscriber and ensures all onXXX methods conform the protocol
(except the requirement for serialized access).
Type parameters:
<T> – the value type/**
 * Wraps another Subscriber and ensures all onXXX methods conform the protocol
 * (except the requirement for serialized access).
 *
 * @param <T> the value type
 */
public final class SafeObserver<T> implements Observer<T>, Disposable {
    
The actual Subscriber. /** The actual Subscriber. */
    final Observer<? super T> downstream;
    
The subscription. /** The subscription. */
    Disposable upstream;
    
Indicates a terminal state. /** Indicates a terminal state. */
    boolean done;

    
Constructs a SafeObserver by wrapping the given actual Observer.
Params:
downstream – the actual Observer to wrap, not null (not validated)/**
     * Constructs a SafeObserver by wrapping the given actual Observer.
     * @param downstream the actual Observer to wrap, not null (not validated)
     */
    public SafeObserver(@NonNull Observer<? super T> downstream) {
        this.downstream = downstream;
    }

    @Override
    public void onSubscribe(@NonNull Disposable d) {
        if (DisposableHelper.validate(this.upstream, d)) {
            this.upstream = d;
            try {
                downstream.onSubscribe(this);
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                done = true;
                // can't call onError because the actual's state may be corrupt at this point
                try {
                    d.dispose();
                } catch (Throwable e1) {
                    Exceptions.throwIfFatal(e1);
                    RxJavaPlugins.onError(new CompositeException(e, e1));
                    return;
                }
                RxJavaPlugins.onError(e);
            }
        }
    }

    @Override
    public void dispose() {
        upstream.dispose();
    }

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

    @Override
    public void onNext(@NonNull T t) {
        if (done) {
            return;
        }
        if (upstream == null) {
            onNextNoSubscription();
            return;
        }

        if (t == null) {
            Throwable ex = new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources.");
            try {
                upstream.dispose();
            } catch (Throwable e1) {
                Exceptions.throwIfFatal(e1);
                onError(new CompositeException(ex, e1));
                return;
            }
            onError(ex);
            return;
        }

        try {
            downstream.onNext(t);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            try {
                upstream.dispose();
            } catch (Throwable e1) {
                Exceptions.throwIfFatal(e1);
                onError(new CompositeException(e, e1));
                return;
            }
            onError(e);
        }
    }

    void onNextNoSubscription() {
        done = true;

        Throwable ex = new NullPointerException("Subscription not set!");

        try {
            downstream.onSubscribe(EmptyDisposable.INSTANCE);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            // can't call onError because the actual's state may be corrupt at this point
            RxJavaPlugins.onError(new CompositeException(ex, e));
            return;
        }
        try {
            downstream.onError(ex);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            // if onError failed, all that's left is to report the error to plugins
            RxJavaPlugins.onError(new CompositeException(ex, e));
        }
    }

    @Override
    public void onError(@NonNull Throwable t) {
        if (done) {
            RxJavaPlugins.onError(t);
            return;
        }
        done = true;

        if (upstream == null) {
            Throwable npe = new NullPointerException("Subscription not set!");

            try {
                downstream.onSubscribe(EmptyDisposable.INSTANCE);
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                // can't call onError because the actual's state may be corrupt at this point
                RxJavaPlugins.onError(new CompositeException(t, npe, e));
                return;
            }
            try {
                downstream.onError(new CompositeException(t, npe));
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                // if onError failed, all that's left is to report the error to plugins
                RxJavaPlugins.onError(new CompositeException(t, npe, e));
            }
            return;
        }

        if (t == null) {
            t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
        }

        try {
            downstream.onError(t);
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);

            RxJavaPlugins.onError(new CompositeException(t, ex));
        }
    }

    @Override
    public void onComplete() {
        if (done) {
            return;
        }

        done = true;

        if (upstream == null) {
            onCompleteNoSubscription();
            return;
        }

        try {
            downstream.onComplete();
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            RxJavaPlugins.onError(e);
        }
    }

    void onCompleteNoSubscription() {

        Throwable ex = new NullPointerException("Subscription not set!");

        try {
            downstream.onSubscribe(EmptyDisposable.INSTANCE);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            // can't call onError because the actual's state may be corrupt at this point
            RxJavaPlugins.onError(new CompositeException(ex, e));
            return;
        }
        try {
            downstream.onError(ex);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            // if onError failed, all that's left is to report the error to plugins
            RxJavaPlugins.onError(new CompositeException(ex, e));
        }
    }

}