/* ========================================================================
 * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace Opc.Ua.PubSub
{
    /// <summary>
    /// component that is specialized in calculating and executing a routine for a given interval
    /// </summary>
    public class IntervalRunner : IDisposable
    {
        private const int kMinInterval = 10;
        private readonly Lock m_lock = new();
        private readonly ILogger m_logger;
        private readonly TimeProvider m_timeProvider;

        private double m_interval = kMinInterval;
        private double m_nextPublishTick;

        /// <summary>
        /// event used to cancel run
        /// </summary>
        private CancellationTokenSource? m_cancellationToken = new();

        /// <summary>
        /// Create new instance of <see cref="IntervalRunner"/>.
        /// </summary>
        public IntervalRunner(
            object? id,
            double interval,
            Func<bool> canExecuteFunc,
            Func<Task> intervalActionAsync,
            ITelemetryContext telemetry,
            TimeProvider? timeProvider = null)
        {
            m_logger = telemetry.CreateLogger<IntervalRunner>();
            Id = id;
            Interval = interval;
            CanExecuteFunc = canExecuteFunc;
            IntervalActionAsync = intervalActionAsync;
            m_timeProvider = timeProvider ?? TimeProvider.System;
        }

        /// <summary>
        /// Identifier of current IntervalRunner
        /// </summary>
        public object? Id { get; }

        /// <summary>
        /// Get/set the Interval between Runs in milliseconds
        /// </summary>
        public double Interval
        {
            get => m_interval;
            set
            {
                lock (m_lock)
                {
                    if (value < kMinInterval)
                    {
                        value = kMinInterval;
                    }

                    m_interval = value;
                }
            }
        }

        /// <summary>
        /// Get the function that decides if the configured action can be executed when the Interval elapses
        /// </summary>
        public Func<bool> CanExecuteFunc { get; }

        /// <summary>
        /// Get the async action that will be executed at each interval
        /// </summary>
        public Func<Task> IntervalActionAsync { get; }

        /// <summary>
        /// Starts the IntervalRunner and makes it ready to execute the code.
        /// </summary>
        public void Start()
        {
            lock (m_lock)
            {
                // m_cancellationToken is only null after Dispose; the existing contract
                // assumes Start is not called after Dispose (latent NRE preserved).
                // TODO: Consider adding ObjectDisposedException check after Dispose.
                if (m_cancellationToken!.IsCancellationRequested)
                {
                    m_cancellationToken.Dispose();
                    m_cancellationToken = new CancellationTokenSource();
                }
            }
            Task.Run(ProcessAsync).ConfigureAwait(false);
            m_logger.LogInformation("IntervalRunner with id: {Id} was started.", Id);
        }

        /// <summary>
        /// Stop the publishing thread.
        /// </summary>
        public virtual void Stop()
        {
            lock (m_lock)
            {
                m_cancellationToken?.Cancel();
            }

            m_logger.LogInformation("IntervalRunner with id: {Id} was stopped.", Id);
        }

        /// <summary>
        /// Releases all resources used by the current instance of the <see cref="UaPublisher"/> class.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        ///  When overridden in a derived class, releases the unmanaged resources used by that class
        ///  and optionally releases the managed resources.
        /// </summary>
        /// <param name="disposing"> true to release both managed and unmanaged resources; false to release only unmanaged resources.</param>
        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                Stop();

                m_cancellationToken?.Dispose();
                m_cancellationToken = null;
            }
        }

        /// <summary>
        /// Periodically executes the .
        /// </summary>
        private async Task ProcessAsync()
        {
            bool isSystemProvider = ReferenceEquals(m_timeProvider, TimeProvider.System);
            long ticksPerMs = Math.Max(1L, m_timeProvider.TimestampFrequency / 1000L);
            lock (m_lock)
            {
                m_nextPublishTick = m_timeProvider.GetTimestamp();
            }
            // m_cancellationToken is only null after Dispose; ProcessAsync is started
            // by Start before Dispose can be reached in normal usage.
            while (!m_cancellationToken!.IsCancellationRequested)
            {
                long nowTick = m_timeProvider.GetTimestamp();
                double nextPublishTick = 0;

                lock (m_lock)
                {
                    nextPublishTick = m_nextPublishTick;
                }

                double sleepCycle = (nextPublishTick - nowTick) / ticksPerMs;
                if (sleepCycle > 16)
                {
                    // Use Task.Delay if sleep cycle is larger
                    await m_timeProvider.Delay(
                        TimeSpan.FromMilliseconds(sleepCycle),
                        m_cancellationToken.Token)
                        .ConfigureAwait(false);

                    // Still ticks to consume (spurious wakeup too early), improbable
                    nowTick = m_timeProvider.GetTimestamp();
                    if (nowTick < nextPublishTick)
                    {
                        if (isSystemProvider)
                        {
                            SpinWait.SpinUntil(() => m_timeProvider.GetTimestamp() >= nextPublishTick);
                        }
                        else
                        {
                            double remainingMs = (nextPublishTick - nowTick) / ticksPerMs;
                            if (remainingMs > 0)
                            {
                                await m_timeProvider.Delay(
                                    TimeSpan.FromMilliseconds(remainingMs),
                                    m_cancellationToken.Token)
                                    .ConfigureAwait(false);
                            }
                        }
                    }
                }
                else if (sleepCycle is >= 0 and <= 16)
                {
                    if (isSystemProvider)
                    {
                        SpinWait.SpinUntil(() => m_timeProvider.GetTimestamp() >= nextPublishTick);
                    }
                    else if (sleepCycle > 0)
                    {
                        await m_timeProvider.Delay(
                            TimeSpan.FromMilliseconds(sleepCycle),
                            m_cancellationToken.Token)
                            .ConfigureAwait(false);
                    }
                }

                lock (m_lock)
                {
                    double nextCycle = (long)m_interval * ticksPerMs;
                    m_nextPublishTick += nextCycle;

                    if (IntervalActionAsync != null && CanExecuteFunc != null && CanExecuteFunc())
                    {
                        // call on a new task without blocking the thread pool
                        _ = Task.Run(IntervalActionAsync);
                    }
                }
            }
        }
    }
}