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 java.util.concurrent.atomic.AtomicLong;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.*;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableGenerate<T, S> extends Flowable<T> {
    final Callable<S> stateSupplier;
    final BiFunction<S, Emitter<T>, S> generator;
    final Consumer<? super S> disposeState;

    public FlowableGenerate(Callable<S> stateSupplier, BiFunction<S, Emitter<T>, S> generator,
            Consumer<? super S> disposeState) {
        this.stateSupplier = stateSupplier;
        this.generator = generator;
        this.disposeState = disposeState;
    }

    @Override
    public void subscribeActual(Subscriber<? super T> s) {
        S state;

        try {
            state = stateSupplier.call();
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            EmptySubscription.error(e, s);
            return;
        }

        s.onSubscribe(new GeneratorSubscription<T, S>(s, generator, disposeState, state));
    }

    static final class GeneratorSubscription<T, S>
    extends AtomicLong
    implements Emitter<T>, Subscription {

        private static final long serialVersionUID = 7565982551505011832L;

        final Subscriber<? super T> downstream;
        final BiFunction<S, ? super Emitter<T>, S> generator;
        final Consumer<? super S> disposeState;

        S state;

        volatile boolean cancelled;

        boolean terminate;

        boolean hasNext;

        GeneratorSubscription(Subscriber<? super T> actual,
                BiFunction<S, ? super Emitter<T>, S> generator,
                Consumer<? super S> disposeState, S initialState) {
            this.downstream = actual;
            this.generator = generator;
            this.disposeState = disposeState;
            this.state = initialState;
        }

        @Override
        public void request(long n) {
            if (!SubscriptionHelper.validate(n)) {
                return;
            }
            if (BackpressureHelper.add(this, n) != 0L) {
                return;
            }

            long e = 0L;

            S s = state;

            final BiFunction<S, ? super Emitter<T>, S> f = generator;

            for (;;) {
                while (e != n) {

                    if (cancelled) {
                        state = null;
                        dispose(s);
                        return;
                    }

                    hasNext = false;

                    try {
                        s = f.apply(s, this);
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        cancelled = true;
                        state = null;
                        onError(ex);
                        dispose(s);
                        return;
                    }

                    if (terminate) {
                        cancelled = true;
                        state = null;
                        dispose(s);
                        return;
                    }

                    e++;
                }

                n = get();
                if (e == n) {
                    state = s;
                    n = addAndGet(-e);
                    if (n == 0L) {
                        break;
                    }
                    e = 0L;
                }
            }
        }

        private void dispose(S s) {
            try {
                disposeState.accept(s);
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                RxJavaPlugins.onError(ex);
            }
        }

        @Override
        public void cancel() {
            if (!cancelled) {
                cancelled = true;

                // if there are no running requests, just dispose the state
                if (BackpressureHelper.add(this, 1) == 0) {
                    S s = state;
                    state = null;
                    dispose(s);
                }
            }
        }

        @Override
        public void onNext(T t) {
            if (!terminate) {
                if (hasNext) {
                    onError(new IllegalStateException("onNext already called in this generate turn"));
                } else {
                    if (t == null) {
                        onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
                    } else {
                        hasNext = true;
                        downstream.onNext(t);
                    }
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (terminate) {
                RxJavaPlugins.onError(t);
            } else {
                if (t == null) {
                    t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
                }
                terminate = true;
                downstream.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (!terminate) {
                terminate = true;
                downstream.onComplete();
            }
        }
    }
}