using System;
using System.Collections.Generic;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.Deploy;
using Umbraco.Extensions;

namespace Umbraco.Cms.Core
{
    public static class UdiParserServiceConnectors
    {
        // notes - see U4-10409
        // if this class is used during application pre-start it cannot scans the assemblies,
        // this is addressed by lazily-scanning, with the following caveats:
        // - parsing a root udi still requires a scan and therefore still breaks
        // - parsing an invalid udi ("umb://should-be-guid/<not-a-guid>") corrupts KnowUdiTypes

        private static volatile bool _scanned;
        private static readonly object ScanLocker = new object();

        /// <summary>
        /// Scan for deploy <see cref="IServiceConnector"/> in assemblies for known UDI types.
        /// </summary>
        /// <param name="typeLoader"></param>
        public static void ScanDeployServiceConnectorsForUdiTypes(TypeLoader typeLoader)
        {
            if (typeLoader is null)
                throw new ArgumentNullException(nameof(typeLoader));

            if (_scanned) return;

            lock (ScanLocker)
            {
                // Scan for unknown UDI types
                // there is no way we can get the "registered" service connectors, as registration
                // happens in Deploy, not in Core, and the Udi class belongs to Core - therefore, we
                // just pick every service connectors - just making sure that not two of them
                // would register the same entity type, with different udi types (would not make
                // much sense anyways)
                var connectors = typeLoader.GetTypes<IServiceConnector>();
                var result = new Dictionary<string, UdiType>();
                foreach (var connector in connectors)
                {
                    var attrs = connector.GetCustomAttributes<UdiDefinitionAttribute>(false);
                    foreach (var attr in attrs)
                    {
                        if (result.TryGetValue(attr.EntityType, out var udiType) && udiType != attr.UdiType)
                            throw new Exception(string.Format("Entity type \"{0}\" is declared by more than one IServiceConnector, with different UdiTypes.", attr.EntityType));
                        result[attr.EntityType] = attr.UdiType;
                    }
                }

                // merge these into the known list
                foreach (var item in result)
                    UdiParser.RegisterUdiType(item.Key, item.Value);

                _scanned = true;
            }
        }

        /// <summary>
        /// Registers a single <see cref="IServiceConnector"/> to add it's UDI type.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        public static void RegisterServiceConnector<T>()
            where T: IServiceConnector
        {
            var result = new Dictionary<string, UdiType>();
            var connector = typeof(T);
            var attrs = connector.GetCustomAttributes<UdiDefinitionAttribute>(false);
            foreach (var attr in attrs)
            {
                if (result.TryGetValue(attr.EntityType, out var udiType) && udiType != attr.UdiType)
                    throw new Exception(string.Format("Entity type \"{0}\" is declared by more than one IServiceConnector, with different UdiTypes.", attr.EntityType));
                result[attr.EntityType] = attr.UdiType;
            }

            // merge these into the known list
            foreach (var item in result)
                UdiParser.RegisterUdiType(item.Key, item.Value);
        }
    }
}