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/*
 * Copyright (c) 2016-2022 VMware Inc. or its affiliates, All Rights Reserved.
 *
 * 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
 *
 *   https://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 reactor.core.publisher;

import java.util.Objects;
import java.util.function.Consumer;

import org.reactivestreams.Subscription;

import reactor.core.CoreSubscriber;
import reactor.core.Exceptions;
import reactor.core.Fuseable;
import reactor.core.Fuseable.ConditionalSubscriber;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;
import reactor.util.context.ContextView;

import static reactor.core.Scannable.Attr.RUN_STYLE;
import static reactor.core.Scannable.Attr.RunStyle.SYNC;

/**
 * Peek into the lifecycle events and signals of a sequence
 *
 * @param  the value type
 *
 * @see Reactive-Streams-Commons
 */
final class FluxDoOnEach extends InternalFluxOperator {

	final Consumer> onSignal;

	FluxDoOnEach(Flux source, Consumer> onSignal) {
		super(source);
		this.onSignal = Objects.requireNonNull(onSignal, "onSignal");
	}

	@SuppressWarnings("unchecked")
	static  DoOnEachSubscriber createSubscriber(CoreSubscriber actual,
			Consumer> onSignal, boolean fuseable, boolean isMono) {
		if (fuseable) {
			if(actual instanceof ConditionalSubscriber) {
				return new DoOnEachFuseableConditionalSubscriber<>((ConditionalSubscriber) actual, onSignal, isMono);
			}
			return new DoOnEachFuseableSubscriber<>(actual, onSignal, isMono);
		}

		if (actual instanceof ConditionalSubscriber) {
			return new DoOnEachConditionalSubscriber<>((ConditionalSubscriber) actual, onSignal, isMono);
		}
		return new DoOnEachSubscriber<>(actual, onSignal, isMono);
	}

	@Override
	public CoreSubscriber subscribeOrReturn(CoreSubscriber actual) {
		return createSubscriber(actual, onSignal, false, false);
	}

	@Override
	public Object scanUnsafe(Attr key) {
		if (key == RUN_STYLE) return SYNC;
		return super.scanUnsafe(key);
	}

	static class DoOnEachSubscriber implements InnerOperator, Signal {

		static final short STATE_FLUX_START   = (short) 0;
		static final short STATE_MONO_START   = (short) 1;
		static final short STATE_SKIP_HANDLER = (short) 2;
		static final short STATE_DONE         = (short) 3;

		final CoreSubscriber   actual;
		final Context                     cachedContext;
		final Consumer> onSignal;

		T t;

		Subscription s;
		@Nullable
		Fuseable.QueueSubscription qs;

		short state;

		DoOnEachSubscriber(CoreSubscriber actual,
				Consumer> onSignal,
				boolean monoFlavor) {
			this.actual = actual;
			this.cachedContext = actual.currentContext();
			this.onSignal = onSignal;
			this.state = monoFlavor ? STATE_MONO_START : STATE_FLUX_START;
		}

		@Override
		public void request(long n) {
			s.request(n);
		}

		@Override
		public void cancel() {
			s.cancel();
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;
				this.qs = Operators.as(s);
				actual.onSubscribe(this);
			}
		}

		@Override
		public Context currentContext() {
			return cachedContext;
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.PARENT) {
				return s;
			}
			if (key == Attr.TERMINATED) {
				return state == STATE_DONE;
			}
			if (key == RUN_STYLE) {
			    return SYNC;
			}

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public void onNext(T t) {
			if (state == STATE_DONE) {
				Operators.onNextDropped(t, cachedContext);
				return;
			}
			try {
				this.t = t;
				onSignal.accept(this);
			}
			catch (Throwable e) {
				onError(Operators.onOperatorError(s, e, t, cachedContext));
				return;
			}

			if (state == STATE_MONO_START) {
				state = STATE_SKIP_HANDLER;
				try {
					onSignal.accept(Signal.complete(cachedContext));
				}
				catch (Throwable e) {
					state = STATE_MONO_START;
					onError(Operators.onOperatorError(s, e, cachedContext));
					return;
				}
			}

			actual.onNext(t);
		}

		@Override
		public void onError(Throwable t) {
			if (state == STATE_DONE) {
				Operators.onErrorDropped(t, cachedContext);
				return;
			}
			boolean applyHandler = state < STATE_SKIP_HANDLER;
			state = STATE_DONE;
			if (applyHandler) {
				try {
					onSignal.accept(Signal.error(t, cachedContext));
				}
				catch (Throwable e) {
					//this performs a throwIfFatal or suppresses t in e
					t = Operators.onOperatorError(null, e, t, cachedContext);
				}
			}

			try {
				actual.onError(t);
			}
			catch (UnsupportedOperationException use) {
				if (!Exceptions.isErrorCallbackNotImplemented(use) && use.getCause() != t) {
					throw use;
				}
				//ignore if missing callback
			}
		}

		@Override
		public void onComplete() {
			if (state == STATE_DONE) {
				return;
			}
			short oldState = state;
			state = STATE_DONE;
			if (oldState < STATE_SKIP_HANDLER) {
				try {
					onSignal.accept(Signal.complete(cachedContext));
				}
				catch (Throwable e) {
					state = oldState;
					onError(Operators.onOperatorError(s, e, cachedContext));
					return;
				}
			}

			actual.onComplete();
		}

		@Override
		public CoreSubscriber actual() {
			return actual;
		}

		@Nullable
		@Override
		public Throwable getThrowable() {
			return null;
		}

		@Nullable
		@Override
		public Subscription getSubscription() {
			return null;
		}

		@Nullable
		@Override
		public T get() {
			return t;
		}

		@Override
		public ContextView getContextView() {
			return cachedContext;
		}

		@Override
		public SignalType getType() {
			return SignalType.ON_NEXT;
		}

		@Override
		public String toString() {
			return "doOnEach_onNext(" + t + ")";
		}
	}

	static class DoOnEachFuseableSubscriber extends DoOnEachSubscriber
			implements Fuseable, Fuseable.QueueSubscription {

		int fusionMode;

		DoOnEachFuseableSubscriber(CoreSubscriber actual,
				Consumer> onSignal, boolean isMono) {
			super(actual, onSignal, isMono);
		}

		@Override
		public void onNext(T t) {
			if (this.fusionMode == Fuseable.ASYNC) {
				actual.onNext(null);
				return;
			}
			super.onNext(t);
		}

		@Override
		public int requestFusion(int mode) {
			QueueSubscription qs = this.qs;
			if (qs != null && (mode & Fuseable.THREAD_BARRIER) == 0) {
				int m = qs.requestFusion(mode);
				if (m == Fuseable.SYNC || m == Fuseable.ASYNC) {
					this.fusionMode = m;
					return m;
				}
			}
			this.fusionMode = NONE;
			return Fuseable.NONE;
		}

		@Override
		public void clear() {
			qs.clear(); //throws NPE, but should only be called after onSubscribe on a Fuseable
		}

		@Override
		public boolean isEmpty() {
			return qs == null || qs.isEmpty();
		}

		@Override
		@Nullable
		public T poll() {
			if (qs == null) {
				return null;
			}
			T v = qs.poll();
			if (v == null && this.fusionMode == SYNC) {
				state = STATE_DONE;
				try {
					onSignal.accept(Signal.complete(cachedContext));
				}
				catch (Throwable e) {
					throw e;
				}
			} else if (v != null) {
				this.t = v;
				onSignal.accept(this); //throws in case of error
			}
			return v;
		}

		@Override
		public int size() {
			return qs == null ? 0 : qs.size();
		}
	}

	static final class DoOnEachConditionalSubscriber extends DoOnEachSubscriber
			implements ConditionalSubscriber {

		DoOnEachConditionalSubscriber(ConditionalSubscriber actual,
				Consumer> onSignal, boolean isMono) {
			super(actual, onSignal, isMono);
		}

		@Override
		@SuppressWarnings("unchecked")
		public boolean tryOnNext(T t) {
			boolean result = ((ConditionalSubscriber)actual).tryOnNext(t);
			if (result) {
				this.t = t;
				onSignal.accept(this);
				//TODO also apply the handler with onComplete if there is a way to trigger tryOnNext from a Mono?
				//TODO if so, should `tryOnNext` be called first?
			}
			return result;
		}
	}

	static final class DoOnEachFuseableConditionalSubscriber extends DoOnEachFuseableSubscriber
			implements ConditionalSubscriber {

		DoOnEachFuseableConditionalSubscriber(ConditionalSubscriber actual,
				Consumer> onSignal, boolean isMono) {
			super(actual, onSignal, isMono);
		}

		@Override
		@SuppressWarnings("unchecked")
		public boolean tryOnNext(T t) {
			boolean result = ((ConditionalSubscriber) actual).tryOnNext(t);
			if (result) {
				this.t = t;
				onSignal.accept(this);
				//TODO also apply the handler with onComplete if there is a way to trigger tryOnNext from a Mono?
			}
			return result;
		}
	}
}