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/*
 * Copyright 2021-2024 the original author or authors.
 *
 * 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 com.metaeffekt.mirror.concurrency;

import org.apache.commons.lang3.tuple.Pair;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

public class ScheduledDelayedThreadPoolExecutor {

    private final static Logger LOG = LoggerFactory.getLogger(ScheduledDelayedThreadPoolExecutor.class);
    protected final static int LOG_PROGRESS_EVERY_PERCENT = 25;

    private ScheduledThreadPoolExecutor executor;
    private final BlockingQueue backlog;

    private final AtomicInteger remainingScheduledTasks = new AtomicInteger(0);
    private final AtomicInteger maxTaskListSize = new AtomicInteger(0);
    private final AtomicLong batchStartTime = new AtomicLong();
    private final AtomicLong currentBatchEndTime = new AtomicLong();
    private final AtomicLong lastLoggedProgressPercent = new AtomicLong();

    private final List> exceptions = Collections.synchronizedList(new ArrayList<>());

    private long delay;
    private boolean logProgress = true;
    private int logEveryPercent = LOG_PROGRESS_EVERY_PERCENT;

    public ScheduledDelayedThreadPoolExecutor(int size, long delay) {
        this.executor = this.createExecutor(size);
        this.backlog = new LinkedBlockingQueue<>();
        this.setDelay(delay);
        this.currentBatchEndTime.set(System.currentTimeMillis());
    }

    public void setSize(int size) {
        if (size <= 0) throw new IllegalArgumentException("Size must be greater than 0");
        final int maxThreads = Math.max(1, Math.min(size, Runtime.getRuntime().availableProcessors() - 1));
        this.executor.setCorePoolSize(maxThreads);
    }

    public void setDelay(long delay) {
        if (delay < 0) throw new IllegalArgumentException("Delay must be non-negative");
        this.delay = delay;
    }

    public void setLogProgress(boolean logProgress) {
        this.logProgress = logProgress;
    }

    public void setLogEveryPercent(int logEveryPercent) {
        this.logEveryPercent = logEveryPercent;
    }

    public void submit(ThrowingRunnable task) {
        if (task == null) throw new IllegalArgumentException("Task must not be null");
        if (task instanceof Thread) {
            LOG.warn("Thread [{}] submitted to executor. Use Runnable instead", ((Thread) task).getName());
        }
        this.backlog.offer(task);
    }

    public void start() {
        final long startTime = System.currentTimeMillis();
        batchStartTime.set(startTime);
        final long timeRemainingUntilDone = currentBatchEndTime.get() - startTime;

        long delay;
        if (timeRemainingUntilDone > 0) {
            delay = timeRemainingUntilDone + this.delay;
        } else {
            delay = this.delay;
        }

        while (!backlog.isEmpty()) {
            executor.schedule(backlog.poll(), delay, TimeUnit.MILLISECONDS);
            delay += this.delay;
            remainingScheduledTasks.incrementAndGet();
        }
        currentBatchEndTime.set(System.currentTimeMillis() + delay - this.delay);

        maxTaskListSize.set(Math.max(maxTaskListSize.get(), remainingScheduledTasks.get()));
    }

    public void join() throws InterruptedException {
        executor.shutdown();
        while (!executor.awaitTermination(5, TimeUnit.MINUTES)) {
            LOG.info("Waiting for executor to terminate");
        }
        final int corePoolSize = executor.getCorePoolSize();
        executor = this.createExecutor(corePoolSize);

        remainingScheduledTasks.set(0);
        maxTaskListSize.set(0);
        lastLoggedProgressPercent.set(0);
        currentBatchEndTime.set(System.currentTimeMillis());

        LOG.info("Executor terminated");

        if (!exceptions.isEmpty()) {
            throw new RuntimeException(exceptions.size() + " exceptions occurred during execution. See log for details.");
        }
    }

    public boolean isRunning() {
        if (executor.isTerminated()) {
            return false;
        }
        return remainingScheduledTasks.get() > 0;
    }

    private int calculateRemainingPercent() {
        final double remainingTasks = remainingScheduledTasks.get();
        final double maxTasks = maxTaskListSize.get();

        if (maxTasks == 0) return 0;

        return (int) (100 - (remainingTasks / (maxTasks / 100)));
    }

    private long calculateEstimatedTimeRemaining() {
        final long completedTasks = maxTaskListSize.get() - remainingScheduledTasks.get();
        if (completedTasks == 0) return 0;

        final long elapsedTime = System.currentTimeMillis() - batchStartTime.get();
        final long averageTaskTime = elapsedTime / completedTasks;

        return averageTaskTime * remainingScheduledTasks.get();
    }

    private boolean shouldProgressBeLogged() {
        if (!logProgress) return false;

        final long lastLoggedProgress = this.lastLoggedProgressPercent.get();
        final long currentProgress = calculateRemainingPercent();

        if (currentProgress == 0) return false;

        if (currentProgress - lastLoggedProgress >= this.logEveryPercent) {
            this.lastLoggedProgressPercent.set(currentProgress);
            return true;
        }

        return false;
    }

    private ScheduledThreadPoolExecutor createExecutor(int size) {
        return new ScheduledThreadPoolExecutor(size) {
            @Override
            protected void afterExecute(Runnable r, Throwable t) {
                super.afterExecute(r, t);
                remainingScheduledTasks.decrementAndGet();

                if (shouldProgressBeLogged()) {
                    final int remainingPercent = calculateRemainingPercent();

                    // TODO: properly calculate time remaining, then show it in the log message
                    final long estimatedTimeRemaining = calculateEstimatedTimeRemaining();
                    final long estimatedTimeRemainingSecs = TimeUnit.MILLISECONDS.toSeconds(estimatedTimeRemaining);

                    LOG.info("Started [{} / {}] tasks [{} %]",
                            maxTaskListSize.get() - remainingScheduledTasks.get(),
                            maxTaskListSize.get(),
                            remainingPercent);
                }

                if (t == null && r instanceof Future) {
                    try {
                        Future future = (Future) r;
                        if (future.isDone()) {
                            future.get();
                        }
                    } catch (CancellationException ce) {
                        t = ce;
                    } catch (ExecutionException ee) {
                        t = ee.getCause();
                    } catch (InterruptedException ie) {
                        Thread.currentThread().interrupt(); // propagate interrupt
                    }
                }
                if (t != null) {
                    if (t instanceof ThrowingRunnableException) {
                        t = t.getCause();
                    }
                    exceptions.add(Pair.of(maxTaskListSize.get() - remainingScheduledTasks.get(), t));
                    throw new RuntimeException("Exception in scheduled task at ~" + (maxTaskListSize.get() - remainingScheduledTasks.get()), t);
                }
            }
        };
    }

    private static class ThrowingRunnableException extends RuntimeException {
        public ThrowingRunnableException(String message) {
            super(message);
        }

        public ThrowingRunnableException(String message, Throwable cause) {
            super(message, cause);
        }

        public ThrowingRunnableException(Throwable cause) {
            super(cause);
        }
    }

    public interface ThrowingRunnable extends Runnable {
        @Override
        default void run() {
            try {
                runThrows();
            } catch (Exception e) {
                throw new ThrowingRunnableException(e);
            }
        }

        void runThrows() throws Exception;
    }
}