/*
 * 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.rxjava3.internal.operators.flowable;

import java.util.*;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.rxjava3.core.*;
import io.reactivex.rxjava3.core.Scheduler.Worker;
import io.reactivex.rxjava3.exceptions.MissingBackpressureException;
import io.reactivex.rxjava3.internal.disposables.SequentialDisposable;
import io.reactivex.rxjava3.internal.fuseable.SimplePlainQueue;
import io.reactivex.rxjava3.internal.queue.MpscLinkedQueue;
import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
import io.reactivex.rxjava3.internal.util.BackpressureHelper;
import io.reactivex.rxjava3.processors.UnicastProcessor;

public final class FlowableWindowTimed<T> extends AbstractFlowableWithUpstream<T, Flowable<T>> {
    final long timespan;
    final long timeskip;
    final TimeUnit unit;
    final Scheduler scheduler;
    final long maxSize;
    final int bufferSize;
    final boolean restartTimerOnMaxSize;

    public FlowableWindowTimed(Flowable<T> source,
            long timespan, long timeskip, TimeUnit unit, Scheduler scheduler, long maxSize,
            int bufferSize, boolean restartTimerOnMaxSize) {
        super(source);
        this.timespan = timespan;
        this.timeskip = timeskip;
        this.unit = unit;
        this.scheduler = scheduler;
        this.maxSize = maxSize;
        this.bufferSize = bufferSize;
        this.restartTimerOnMaxSize = restartTimerOnMaxSize;
    }

    @Override
    protected void subscribeActual(Subscriber<? super Flowable<T>> downstream) {
        if (timespan == timeskip) {
            if (maxSize == Long.MAX_VALUE) {
                source.subscribe(new WindowExactUnboundedSubscriber<>(
                        downstream,
                        timespan, unit, scheduler, bufferSize));
                return;
            }
            source.subscribe(new WindowExactBoundedSubscriber<>(
                        downstream,
                        timespan, unit, scheduler,
                        bufferSize, maxSize, restartTimerOnMaxSize));
            return;
        }
        source.subscribe(new WindowSkipSubscriber<>(downstream,
                timespan, timeskip, unit, scheduler.createWorker(), bufferSize));
    }

    abstract static class AbstractWindowSubscriber<T>
    extends AtomicInteger
    implements FlowableSubscriber<T>, Subscription {
        private static final long serialVersionUID = 5724293814035355511L;

        final Subscriber<? super Flowable<T>> downstream;

        final SimplePlainQueue<Object> queue;

        final long timespan;
        final TimeUnit unit;
        final int bufferSize;

        final AtomicLong requested;
        long emitted;

        volatile boolean done;
        Throwable error;

        Subscription upstream;

        final AtomicBoolean downstreamCancelled;

        volatile boolean upstreamCancelled;

        final AtomicInteger windowCount;

        AbstractWindowSubscriber(Subscriber<? super Flowable<T>> downstream, long timespan, TimeUnit unit, int bufferSize) {
            this.downstream = downstream;
            this.queue = new MpscLinkedQueue<>();
            this.timespan = timespan;
            this.unit = unit;
            this.bufferSize = bufferSize;
            this.requested = new AtomicLong();
            this.downstreamCancelled = new AtomicBoolean();
            this.windowCount = new AtomicInteger(1);
        }

        @Override
        public final void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;

                downstream.onSubscribe(this);

                createFirstWindow();
            }
        }

        abstract void createFirstWindow();

        @Override
        public final void onNext(T t) {
            queue.offer(t);
            drain();
        }

        @Override
        public final void onError(Throwable t) {
            error = t;
            done = true;
            drain();
        }

        @Override
        public final void onComplete() {
            done = true;
            drain();
        }

        @Override
        public final void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
            }
        }

        @Override
        public final void cancel() {
            if (downstreamCancelled.compareAndSet(false, true)) {
                windowDone();
            }
        }

        final void windowDone() {
            if (windowCount.decrementAndGet() == 0) {
                cleanupResources();
                upstream.cancel();
                upstreamCancelled = true;
                drain();
            }
        }

        abstract void cleanupResources();

        abstract void drain();
    }

    static final class WindowExactUnboundedSubscriber<T>
            extends AbstractWindowSubscriber<T>
            implements Runnable {

        private static final long serialVersionUID = 1155822639622580836L;

        final Scheduler scheduler;

        UnicastProcessor<T> window;

        final SequentialDisposable timer;

        static final Object NEXT_WINDOW = new Object();

        final Runnable windowRunnable;

        WindowExactUnboundedSubscriber(Subscriber<? super Flowable<T>> actual, long timespan, TimeUnit unit,
                Scheduler scheduler, int bufferSize) {
            super(actual, timespan, unit, bufferSize);
            this.scheduler = scheduler;
            this.timer = new SequentialDisposable();
            this.windowRunnable = new WindowRunnable();
        }

        @Override
        void createFirstWindow() {
            if (!downstreamCancelled.get()) {
                if (requested.get() != 0L) {
                    windowCount.getAndIncrement();
                    window = UnicastProcessor.create(bufferSize, windowRunnable);

                    emitted = 1;

                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                    downstream.onNext(intercept);

                    timer.replace(scheduler.schedulePeriodicallyDirect(this, timespan, timespan, unit));

                    if (intercept.tryAbandon()) {
                        window.onComplete();
                    }

                    upstream.request(Long.MAX_VALUE);
                } else {
                    upstream.cancel();
                    downstream.onError(new MissingBackpressureException(missingBackpressureMessage(emitted)));

                    cleanupResources();
                    upstreamCancelled = true;
                }
            }
        }

        @Override
        public void run() {
            queue.offer(NEXT_WINDOW);
            drain();
        }

        @Override
        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            final SimplePlainQueue<Object> queue = this.queue;
            final Subscriber<? super Flowable<T>> downstream = this.downstream;
            UnicastProcessor<T> window = this.window;

            int missed = 1;
            for (;;) {

                if (upstreamCancelled) {
                    queue.clear();
                    window = null;
                    this.window = null;
                } else {
                    boolean isDone = done;
                    Object o = queue.poll();
                    boolean isEmpty = o == null;

                    if (isDone && isEmpty) {
                        Throwable ex = error;
                        if (ex != null) {
                            if (window != null) {
                                window.onError(ex);
                            }
                            downstream.onError(ex);
                        } else {
                            if (window != null) {
                                window.onComplete();
                            }
                            downstream.onComplete();
                        }
                        cleanupResources();
                        upstreamCancelled = true;
                        continue;
                    }
                    else if (!isEmpty) {

                        if (o == NEXT_WINDOW) {
                            if (window != null) {
                                window.onComplete();
                                window = null;
                                this.window = null;
                            }
                            if (downstreamCancelled.get()) {
                                timer.dispose();
                            } else {
                                if (requested.get() == emitted) {
                                    upstream.cancel();
                                    cleanupResources();
                                    upstreamCancelled = true;

                                    downstream.onError(new MissingBackpressureException(missingBackpressureMessage(emitted)));
                                } else {
                                    emitted++;

                                    windowCount.getAndIncrement();
                                    window = UnicastProcessor.create(bufferSize, windowRunnable);
                                    this.window = window;

                                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                                    downstream.onNext(intercept);

                                    if (intercept.tryAbandon()) {
                                        window.onComplete();
                                    }
                                }
                            }
                        } else if (window != null) {
                            @SuppressWarnings("unchecked")
                            T item = (T)o;
                            window.onNext(item);
                        }

                        continue;
                    }
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        @Override
        void cleanupResources() {
            timer.dispose();
        }

        final class WindowRunnable implements Runnable {
            @Override
            public void run() {
                windowDone();
            }
        }
    }

    static final class WindowExactBoundedSubscriber<T>
    extends AbstractWindowSubscriber<T>
    implements Runnable {
        private static final long serialVersionUID = -6130475889925953722L;

        final Scheduler scheduler;
        final boolean restartTimerOnMaxSize;
        final long maxSize;
        final Scheduler.Worker worker;

        long count;

        UnicastProcessor<T> window;

        final SequentialDisposable timer;

        WindowExactBoundedSubscriber(
                Subscriber<? super Flowable<T>> actual,
                long timespan, TimeUnit unit, Scheduler scheduler,
                int bufferSize, long maxSize, boolean restartTimerOnMaxSize) {
            super(actual, timespan, unit, bufferSize);
            this.scheduler = scheduler;
            this.maxSize = maxSize;
            this.restartTimerOnMaxSize = restartTimerOnMaxSize;
            if (restartTimerOnMaxSize) {
                worker = scheduler.createWorker();
            } else {
                worker = null;
            }
            this.timer = new SequentialDisposable();
        }

        @Override
        void createFirstWindow() {
            if (!downstreamCancelled.get()) {
                if (requested.get() != 0L) {
                    emitted = 1;

                    windowCount.getAndIncrement();
                    window = UnicastProcessor.create(bufferSize, this);

                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                    downstream.onNext(intercept);

                    Runnable boundaryTask = new WindowBoundaryRunnable(this, 1L);
                    if (restartTimerOnMaxSize) {
                        timer.replace(worker.schedulePeriodically(boundaryTask, timespan, timespan, unit));
                    } else {
                        timer.replace(scheduler.schedulePeriodicallyDirect(boundaryTask, timespan, timespan, unit));
                    }

                    if (intercept.tryAbandon()) {
                        window.onComplete();
                    }

                    upstream.request(Long.MAX_VALUE);
                } else {
                    upstream.cancel();
                    downstream.onError(new MissingBackpressureException(missingBackpressureMessage(emitted)));

                    cleanupResources();
                    upstreamCancelled = true;
                }
            }
        }

        @Override
        public void run() {
            windowDone();
        }

        @Override
        void cleanupResources() {
            timer.dispose();
            Worker w = worker;
            if (w != null) {
                w.dispose();
            }
        }

        void boundary(WindowBoundaryRunnable sender) {
            queue.offer(sender);
            drain();
        }

        @Override
        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            int missed = 1;
            final SimplePlainQueue<Object> queue = this.queue;
            final Subscriber<? super Flowable<T>> downstream = this.downstream;
            UnicastProcessor<T> window = this.window;

            for (;;) {

                if (upstreamCancelled) {
                    queue.clear();
                    window = null;
                    this.window = null;
                } else {

                    boolean isDone = done;
                    Object o = queue.poll();
                    boolean isEmpty = o == null;

                    if (isDone && isEmpty) {
                        Throwable ex = error;
                        if (ex != null) {
                            if (window != null) {
                                window.onError(ex);
                            }
                            downstream.onError(ex);
                        } else {
                            if (window != null) {
                                window.onComplete();
                            }
                            downstream.onComplete();
                        }
                        cleanupResources();
                        upstreamCancelled = true;
                        continue;
                    } else if (!isEmpty) {
                        if (o instanceof WindowBoundaryRunnable) {
                            WindowBoundaryRunnable boundary = (WindowBoundaryRunnable) o;
                            if (boundary.index == emitted || !restartTimerOnMaxSize) {
                                this.count = 0;
                                window = createNewWindow(window);
                            }
                        } else if (window != null) {
                            @SuppressWarnings("unchecked")
                            T item = (T)o;
                            window.onNext(item);

                            long count = this.count + 1;
                            if (count == maxSize) {
                                this.count = 0;
                                window = createNewWindow(window);
                            } else {
                                this.count = count;
                            }
                        }

                        continue;
                    }
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        UnicastProcessor<T> createNewWindow(UnicastProcessor<T> window) {
            if (window != null) {
                window.onComplete();
                window = null;
            }

            if (downstreamCancelled.get()) {
                cleanupResources();
            } else {
                long emitted = this.emitted;
                if (requested.get() == emitted) {
                    upstream.cancel();
                    cleanupResources();
                    upstreamCancelled = true;

                    downstream.onError(new MissingBackpressureException(missingBackpressureMessage(emitted)));
                } else {
                    this.emitted = ++emitted;

                    windowCount.getAndIncrement();
                    window = UnicastProcessor.create(bufferSize, this);
                    this.window = window;

                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                    downstream.onNext(intercept);

                    if (restartTimerOnMaxSize) {
                        timer.update(worker.schedulePeriodically(new WindowBoundaryRunnable(this, emitted), timespan, timespan, unit));
                    }

                    if (intercept.tryAbandon()) {
                        window.onComplete();
                    }
                }
            }

            return window;
        }

        static final class WindowBoundaryRunnable implements Runnable {

            final WindowExactBoundedSubscriber<?> parent;

            final long index;

            WindowBoundaryRunnable(WindowExactBoundedSubscriber<?> parent, long index) {
                this.parent = parent;
                this.index = index;
            }

            @Override
            public void run() {
                parent.boundary(this);
            }
        }
    }

    static final class WindowSkipSubscriber<T>
    extends AbstractWindowSubscriber<T>
    implements Runnable {
        private static final long serialVersionUID = -7852870764194095894L;

        final long timeskip;
        final Scheduler.Worker worker;

        final List<UnicastProcessor<T>> windows;

        WindowSkipSubscriber(Subscriber<? super Flowable<T>> actual,
                long timespan, long timeskip, TimeUnit unit,
                Worker worker, int bufferSize) {
            super(actual, timespan, unit, bufferSize);
            this.timeskip = timeskip;
            this.worker = worker;
            this.windows = new LinkedList<>();
        }

        @Override
        void createFirstWindow() {
            if (!downstreamCancelled.get()) {
                if (requested.get() != 0L) {
                    emitted = 1;

                    windowCount.getAndIncrement();
                    UnicastProcessor<T> window = UnicastProcessor.create(bufferSize, this);
                    windows.add(window);

                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                    downstream.onNext(intercept);

                    worker.schedule(new WindowBoundaryRunnable(this, false), timespan, unit);
                    worker.schedulePeriodically(new WindowBoundaryRunnable(this, true), timeskip, timeskip, unit);

                    if (intercept.tryAbandon()) {
                        window.onComplete();
                        windows.remove(window);
                    }

                    upstream.request(Long.MAX_VALUE);
                } else {
                    upstream.cancel();
                    downstream.onError(new MissingBackpressureException(missingBackpressureMessage(emitted)));

                    cleanupResources();
                    upstreamCancelled = true;
                }
            }
        }

        @Override
        void cleanupResources() {
            worker.dispose();
        }

        @Override
        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            int missed = 1;
            final SimplePlainQueue<Object> queue = this.queue;
            final Subscriber<? super Flowable<T>> downstream = this.downstream;
            final List<UnicastProcessor<T>> windows = this.windows;

            for (;;) {
                if (upstreamCancelled) {
                    queue.clear();
                    windows.clear();
                } else {
                    boolean isDone = done;
                    Object o = queue.poll();
                    boolean isEmpty = o == null;

                    if (isDone && isEmpty) {
                        Throwable ex = error;
                        if (ex != null) {
                            for (UnicastProcessor<T> window : windows) {
                                window.onError(ex);
                            }
                            downstream.onError(ex);
                        } else {
                            for (UnicastProcessor<T> window : windows) {
                                window.onComplete();
                            }
                            downstream.onComplete();
                        }
                        cleanupResources();
                        upstreamCancelled = true;
                        continue;
                    } else if (!isEmpty) {
                        if (o == WINDOW_OPEN) {
                            if (!downstreamCancelled.get()) {
                                long emitted = this.emitted;
                                if (requested.get() != emitted) {
                                    this.emitted = ++emitted;

                                    windowCount.getAndIncrement();
                                    UnicastProcessor<T> window = UnicastProcessor.create(bufferSize, this);
                                    windows.add(window);

                                    FlowableWindowSubscribeIntercept<T> intercept = new FlowableWindowSubscribeIntercept<>(window);
                                    downstream.onNext(intercept);

                                    worker.schedule(new WindowBoundaryRunnable(this, false), timespan, unit);

                                    if (intercept.tryAbandon()) {
                                        window.onComplete();
                                    }
                                } else {
                                    upstream.cancel();
                                    Throwable ex = new MissingBackpressureException(missingBackpressureMessage(emitted));
                                    for (UnicastProcessor<T> window : windows) {
                                        window.onError(ex);
                                    }
                                    downstream.onError(ex);

                                    cleanupResources();
                                    upstreamCancelled = true;
                                    continue;
                                }
                            }
                        } else if (o == WINDOW_CLOSE) {
                            if (!windows.isEmpty()) {
                                windows.remove(0).onComplete();
                            }
                        } else {
                            @SuppressWarnings("unchecked")
                            T item = (T)o;
                            for (UnicastProcessor<T> window : windows) {
                                window.onNext(item);
                            }
                        }
                        continue;
                    }
                }
                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        @Override
        public void run() {
            windowDone();
        }

        void boundary(boolean isOpen) {
            queue.offer(isOpen ? WINDOW_OPEN : WINDOW_CLOSE);
            drain();
        }

        static final Object WINDOW_OPEN = new Object();
        static final Object WINDOW_CLOSE = new Object();

        static final class WindowBoundaryRunnable implements Runnable {

            final WindowSkipSubscriber<?> parent;

            final boolean isOpen;

            WindowBoundaryRunnable(WindowSkipSubscriber<?> parent, boolean isOpen) {
                this.parent = parent;
                this.isOpen = isOpen;
            }

            @Override
            public void run() {
                parent.boundary(isOpen);
            }
        }
    }

    static String missingBackpressureMessage(long index) {
        return "Unable to emit the next window (#" + index + ") due to lack of requests. Please make sure the downstream is ready to consume windows.";
    }

}
