/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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 org.apache.commons.exec;

import java.time.Duration;
import java.util.Vector;
import java.util.concurrent.ThreadFactory;
import java.util.function.Supplier;

/**
 * Generalization of {@code ExecuteWatchdog}.
 *
 * @see org.apache.commons.exec.ExecuteWatchdog
 */
public class Watchdog implements Runnable {

    /**
     * Builds ExecuteWatchdog instances.
     *
     * @since 1.4.0
     */
    public static final class Builder implements Supplier<Watchdog> {

        private ThreadFactory threadFactory;
        private Duration timeout;

        /**
         * Constructs a new instance.
         */
        public Builder() {
            // empty
        }

        /**
         * Creates a new configured ExecuteWatchdog.
         *
         * @return a new configured ExecuteWatchdog.
         */
        @Override
        public Watchdog get() {
            return new Watchdog(threadFactory, timeout);
        }

        /**
         * Sets the thread factory.
         *
         * @param threadFactory the thread factory.
         * @return {@code this} instance.
         */
        public Builder setThreadFactory(final ThreadFactory threadFactory) {
            this.threadFactory = threadFactory;
            return this;
        }

        /**
         * Sets the timeout duration.
         *
         * @param timeout the timeout duration.
         * @return {@code this} instance.
         */
        public Builder setTimeout(final Duration timeout) {
            this.timeout = timeout;
            return this;
        }

    }

    /**
     * Creates a new builder.
     *
     * @return a new builder.
     * @since 1.4.0
     */
    public static Builder builder() {
        return new Builder();
    }

    private final Vector<TimeoutObserver> observers = new Vector<>(1);

    private final long timeoutMillis;

    private boolean stopped;

    /**
     * The thread factory.
     */
    private final ThreadFactory threadFactory;

    /**
     * Constructs a new instance.
     *
     * @param timeoutMillis the timeout duration.
     * @deprecated Use {@link Builder#get()}.
     */
    @Deprecated
    public Watchdog(final long timeoutMillis) {
        this(null, Duration.ofMillis(timeoutMillis));
    }

    /**
     * Constructs a new instance.
     *
     * @param threadFactory the thread factory.
     * @param timeout       the timeout duration.
     */
    private Watchdog(final ThreadFactory threadFactory, final Duration timeout) {
        if (timeout.isNegative() || Duration.ZERO.equals(timeout)) {
            throw new IllegalArgumentException("timeout must not be less than 1.");
        }
        this.timeoutMillis = timeout.toMillis();
        this.threadFactory = threadFactory;
    }

    /**
     * Adds a TimeoutObserver.
     *
     * @param to a TimeoutObserver to add.
     */
    public void addTimeoutObserver(final TimeoutObserver to) {
        observers.addElement(to);
    }

    /**
     * Fires a timeout occurred event for each observer.
     */
    protected final void fireTimeoutOccured() {
        observers.forEach(o -> o.timeoutOccured(this));
    }

    /**
     * Removes a TimeoutObserver.
     *
     * @param to a TimeoutObserver to remove.
     */
    public void removeTimeoutObserver(final TimeoutObserver to) {
        observers.removeElement(to);
    }

    @Override
    public void run() {
        final long startTimeMillis = System.currentTimeMillis();
        boolean isWaiting;
        synchronized (this) {
            long timeLeftMillis = timeoutMillis - (System.currentTimeMillis() - startTimeMillis);
            isWaiting = timeLeftMillis > 0;
            while (!stopped && isWaiting) {
                try {
                    wait(timeLeftMillis);
                } catch (final InterruptedException ignore) {
                    // ignore
                }
                timeLeftMillis = timeoutMillis - (System.currentTimeMillis() - startTimeMillis);
                isWaiting = timeLeftMillis > 0;
            }
        }

        // notify the listeners outside of the synchronized block (see EXEC-60)
        if (!isWaiting) {
            fireTimeoutOccured();
        }
    }

    /**
     * Starts a new thread.
     */
    public synchronized void start() {
        stopped = false;
        ThreadUtil.newThread(threadFactory, this, "CommonsExecWatchdog-", true).start();
    }

    /**
     * Requests a thread stop.
     */
    public synchronized void stop() {
        stopped = true;
        notifyAll();
    }

}