using System;
using System.Collections.Concurrent;
using System.Diagnostics;
using Microsoft.Extensions.Logging;

namespace AyaNova.Util
{

    /// <summary>
    /// Used by reporting system to ensure headless browsers don't hang around in an untimely manner chewing up resources
    /// needed due to bugs in puppeteersharp where it won't close the browser on timeout properly
    /// also zombie process issues in linux etc, this just ensures it's safe
    /// This is triggered when a report is rendered on demand
    /// in other words demand drives whether it kills long running renders or not
    /// this is by design to allow a scenario where a super long running report can still be run off hours (for example)
    /// </summary>
    internal static class ReportRenderManager
    {
        /*        
            expired processes are removed by the act of tryign to get a new slot so in this way it still supports running super long reports overnight for example as long as there is no contention
            The other way was by a job that looks for expired processes but that would mean all old jobs would expire all the time so there would be an issue with huge reports never working
        */

        //thread safe collection for unordered items, optimized for single thread produce/consume (which is the norm here) but supports multithread produce / consume (which is needed for separate cleanup job)
        private static ConcurrentBag<ReportRenderInstanceInfo> _baginstances = new ConcurrentBag<ReportRenderInstanceInfo>();

        public class ReportRenderInstanceInfo
        {
            public int ReporterProcessId { get; set; }
            public DateTime Expires { get; set; }

            public ReportRenderInstanceInfo(int processId)
            {
                ReporterProcessId = processId;
                Expires = DateTime.UtcNow.AddMilliseconds(ServerBootConfig.AYANOVA_REPORT_RENDERING_TIMEOUT);
            }
        }


        public static bool RenderSlotAvailable(ILogger log)
        {
            log.LogTrace("RenderSlotAvailable check");
            var count = _baginstances.Count;
// #if (DEBUG)
//             log.LogInformation($"DBG: RenderSlotAvailable check, there are currently {count} instances in the bag");
// #endif
            if (count >= ServerBootConfig.AYANOVA_REPORT_RENDERING_MAX_INSTANCES)
            {
                log.LogTrace($"RenderSlotAvailable there are no free report rendering slots available, current count is {count}, checking for expired slots to force closed");
                //check for expired and remove
                var Instances = _baginstances.ToArray();
                var dtNow = DateTime.UtcNow;
                foreach (ReportRenderInstanceInfo i in Instances)
                {
                    if (i.Expires < dtNow)
                    {
// #if (DEBUG)
//                         log.LogInformation($"DBG: RenderSlotAvailable attempting kill of expired process {i.ReporterProcessId}");
// #endif
                        ForceCloseProcess(i, log);
                    }
                }
            }
            //allow to continue if there are now fewer than max instances in the bag
            return _baginstances.Count < ServerBootConfig.AYANOVA_REPORT_RENDERING_MAX_INSTANCES;
        }

        private static bool ForceCloseProcess(ReportRenderInstanceInfo instance, ILogger log)
        {
            log.LogTrace($"ForceCloseProcess on instance id {instance.ReporterProcessId} started {instance.Expires.ToString()} utc");
            try
            {
                var p = Process.GetProcessById(instance.ReporterProcessId);
                if (p != null)
                {
                    //we have an existing process                   
                    //try to kill it                   
                    p.Kill();
                    if (p.HasExited == false)
                    {

                        log.LogDebug($"RenderSlotAvailable oldest slot could not be stopped");
                        return false;//can't kill it so can't free up a slot
                    }
                }
                //remove it from the list, it's either gone or killed at this point
                //this would not be unexpected since it will normally just close on it's own
                //at the finally in render report
                _baginstances.TryTake(out instance);
                return true;//process that was there is now not there so while not perfect system we will consider it free

            }
            catch (ArgumentException)
            {
                //do nothing, this is normal, the process could not be found and this means it's already been removed:
                //ArgumentException
                //The process specified by the processId parameter is not running. The identifier might be expired.
                _baginstances.TryTake(out instance);
                return true;
            }           
        }

        internal static void AddProcess(int processId)
        {
            _baginstances.Add(new ReportRenderInstanceInfo(processId));
        }

        internal static void RemoveProcess(int processId, ILogger log)
        {
            foreach (var i in _baginstances)
            {
                if (i.ReporterProcessId == processId)
                {
                    ForceCloseProcess(i, log);
                    break;
                }
            }
        }

    }//eoc
}//eons