using System;
using System.Text.Json;
using System.Net.Sockets;
using System.Net.WebSockets;
using System.Security.Cryptography;

using VNLib.Utils;
using VNLib.Utils.Memory;
using VNLib.Utils.Logging;
using VNLib.Utils.Extensions;
using VNLib.Data.Caching.Extensions;
using VNLib.Net.Messaging.FBM.Client;
using VNLib.Plugins.Extensions.Loading;

namespace VNLib.Plugins.Essentials.Sessions
{
    /// <summary>
    /// A wrapper to simplify a cache client object
    /// </summary>
    public sealed class VnCacheClient : OpenResourceHandle<FBMClient?>
    {
        FBMClient? _client;

        /// <summary>
        /// The wrapped client
        /// </summary>
        public override FBMClient? Resource => _client;


        private TimeSpan RetryInterval;
        
        private readonly ILogProvider? DebugLog;
        private readonly IUnmangedHeap? ClientHeap;

        /// <summary>
        /// Initializes an emtpy client wrapper that still requires 
        /// configuration loading
        /// </summary>
        /// <param name="debugLog">An optional debugging log</param>
        /// <param name="heap">An optional <see cref="IUnmangedHeap"/> for <see cref="FBMClient"/> buffers</param>
        public VnCacheClient(ILogProvider? debugLog, IUnmangedHeap? heap = null)
        {
            DebugLog = debugLog;
            //Default to 10 seconds
            RetryInterval = TimeSpan.FromSeconds(10);

            ClientHeap = heap;
        }

        protected override void Free()
        {
            _client?.Dispose();
            _client = null;
        }

        /// <summary>
        /// Loads required configuration variables from the config store and 
        /// intializes the interal client
        /// </summary>
        /// <param name="config">A dictionary of configuration varables</param>
        /// <exception cref="KeyNotFoundException"></exception>
        public async Task LoadConfigAsync(PluginBase pbase, IReadOnlyDictionary<string, JsonElement> config)
        {
            int maxMessageSize = config["max_message_size"].GetInt32();
            string? brokerAddress = config["broker_address"].GetString() ?? throw new KeyNotFoundException("Missing required configuration variable broker_address");

            //Get keys async
            Task<string?> clientPrivTask = pbase.TryGetSecretAsync("client_private_key");
            Task<string?> brokerPubTask = pbase.TryGetSecretAsync("broker_public_key");

            //Wait for all tasks to complete
            string?[] keys = await Task.WhenAll(clientPrivTask, brokerPubTask);

            byte[] privKey = Convert.FromBase64String(keys[0] ?? throw new KeyNotFoundException("Missing required secret client_private_key"));
            byte[] brokerPub = Convert.FromBase64String(keys[1] ?? throw new KeyNotFoundException("Missing required secret broker_public_key"));
            
            RetryInterval = config["retry_interval_sec"].GetTimeSpan(TimeParseType.Seconds);

            Uri brokerUri = new(brokerAddress);

            //Init the client with default settings
            FBMClientConfig conf = FBMDataCacheExtensions.GetDefaultConfig(ClientHeap ?? Memory.Shared, maxMessageSize, DebugLog);

            _client = new(conf);
            //Add the configuration
            _client.UseBroker(brokerUri)
                .ImportBrokerPublicKey(brokerPub)
                .ImportClientPrivateKey(privKey)
                .UseTls(brokerUri.Scheme == Uri.UriSchemeHttps);

            //Zero the key memory
            Memory.InitializeBlock(privKey.AsSpan());
            Memory.InitializeBlock(brokerPub.AsSpan());
        }

        /// <summary>
        /// Discovers nodes in the configured cluster and connects to a random node
        /// </summary>
        /// <param name="Log">A <see cref="ILogProvider"/> to write log events to</param>
        /// <param name="cancellationToken">A token to cancel the operation</param>
        /// <returns>A task that completes when the operation has been cancelled or an unrecoverable error occured</returns>
        /// <exception cref="InvalidOperationException"></exception>
        /// <exception cref="OperationCanceledException"></exception>
        public async Task RunAsync(ILogProvider Log, CancellationToken cancellationToken)
        {
            _ = Resource ?? throw new InvalidOperationException("Client configuration not loaded, cannot connect to cache servers");

            while (true)
            {
                //Load the server list
                ActiveServer[]? servers;
                while (true)
                {
                    try
                    {
                        Log.Debug("Discovering cluster nodes in broker");
                        //Get server list
                        servers = await Resource.DiscoverNodesAsync(cancellationToken);
                        break;
                    }
                    catch (HttpRequestException re) when (re.InnerException is SocketException)
                    {
                        Log.Warn("Broker server is unreachable");
                    }
                    catch (Exception ex)
                    {
                        Log.Warn("Failed to get server list from broker, reason {r}", ex.Message);
                    }
                    //Gen random ms delay
                    int randomMsDelay = RandomNumberGenerator.GetInt32(1000, 2000);
                    await Task.Delay(randomMsDelay, cancellationToken);
                }
                if (servers?.Length == 0)
                {
                    Log.Warn("No cluster nodes found, retrying");
                    await Task.Delay(RetryInterval, cancellationToken);
                    continue;
                }
                //select random server from the list of servers
                ActiveServer selected = servers!.SelectRandom();
                try
                {
                    Log.Debug("Connecting to server {server}", selected.ServerId);
                    //Try to connect to server
                    await Resource.ConnectAndWaitForExitAsync(selected, cancellationToken);
                    Log.Debug("Cache server disconnected");
                }
                catch (WebSocketException wse)
                {
                    Log.Warn("Failed to connect to cache server {reason}", wse.Message);
                    continue;
                }
                catch (HttpRequestException he) when (he.InnerException is SocketException)
                {
                    Log.Debug("Failed to connect to recommended server {server}", selected.ServerId);
                    //Continue next loop
                    continue;
                }
            }
        }
    }
}