//
// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
//

using System.Collections.Generic;
using Microsoft.SqlTools.Extensibility;
using Microsoft.SqlTools.Hosting;
using Microsoft.SqlTools.Hosting.Protocol;
using Microsoft.SqlTools.ServiceLayer.SqlContext;
using Microsoft.SqlTools.Utility;

namespace Microsoft.SqlTools.ResourceProvider
{
    /// <summary>
    /// Provides support for starting up a service host. This is a common responsibility
    /// for both the main service program and test driver that interacts with it
    /// </summary>
    public static class ResourceProviderHostLoader
    {
        private static object lockObject = new object();
        private static bool isLoaded;

        internal static UtilityServiceHost CreateAndStartServiceHost(SqlToolsContext sqlToolsContext)
        {
            UtilityServiceHost serviceHost = UtilityServiceHost.Instance;
            lock (lockObject)
            {
                if (!isLoaded)
                {
                    // Grab the instance of the service host
                    serviceHost.Initialize();

                    InitializeRequestHandlersAndServices(serviceHost, sqlToolsContext);

                    // Start the service only after all request handlers are setup. This is vital
                    // as otherwise the Initialize event can be lost - it's processed and discarded before the handler
                    // is hooked up to receive the message
                    serviceHost.Start().Wait();
                    isLoaded = true;
                }
            }
            return serviceHost;
        }

        private static void InitializeRequestHandlersAndServices(UtilityServiceHost serviceHost, SqlToolsContext sqlToolsContext)
        {
            // Load extension provider, which currently finds all exports in current DLL. Can be changed to find based
            // on directory or assembly list quite easily in the future
            ExtensionServiceProvider serviceProvider = ExtensionServiceProvider.CreateFromAssembliesInDirectory(GetResourceProviderExtensionDlls());

            serviceProvider.RegisterSingleService(sqlToolsContext);
            serviceProvider.RegisterSingleService(serviceHost);
            
            InitializeHostedServices(serviceProvider, serviceHost);

            serviceHost.InitializeRequestHandlers();
        }

        public static IEnumerable<string> GetResourceProviderExtensionDlls()
        {
            return new string[] {
                "SqlToolsResourceProviderService.dll",
                "Microsoft.SqlTools.ResourceProvider.Core.dll",
                "Microsoft.SqlTools.ResourceProvider.DefaultImpl.dll"
            };
        }

        /// <summary>
        /// Internal to support testing. Initializes <see cref="IHostedService"/> instances in the service,
        /// and registers them for their preferred service type
        /// </summary>
        internal static void InitializeHostedServices(RegisteredServiceProvider provider, IProtocolEndpoint host)
        {
            // Pre-register all services before initializing. This ensures that if one service wishes to reference
            // another one during initialization, it will be able to safely do so
            foreach (IHostedService service in provider.GetServices<IHostedService>())
            {
                provider.RegisterSingleService(service.ServiceType, service);
            }

            foreach (IHostedService service in provider.GetServices<IHostedService>())
            {
                // Initialize all hosted services, and register them in the service provider for their requested
                // service type. This ensures that when searching for the ConnectionService you can get it without
                // searching for an IHostedService of type ConnectionService
                service.InitializeService(host);
            }
        }
    }
}