using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Dispatcher;

namespace Umbraco.Web.WebApi
{
    public class NamespaceHttpControllerSelector : DefaultHttpControllerSelector
    {
        private const string ControllerKey = "controller";
        private readonly HttpConfiguration _configuration;
        private readonly Lazy<ConcurrentStack<NamespaceHttpControllerMetadata>> _duplicateControllerTypes;

        public NamespaceHttpControllerSelector(HttpConfiguration configuration) : base(configuration)
        {
            _configuration = configuration;
            _duplicateControllerTypes = new Lazy<ConcurrentStack<NamespaceHttpControllerMetadata>>(GetDuplicateControllerTypes);
        }

        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            var routeData = request.GetRouteData();
            if (routeData == null 
                || routeData.Route == null
                || routeData.Route.DataTokens == null 
                || routeData.Route.DataTokens["Namespaces"] == null)
                return base.SelectController(request);
            
            // Look up controller in route data
            object controllerName;
            routeData.Values.TryGetValue(ControllerKey, out controllerName);
            var controllerNameAsString = controllerName as string;
            if (controllerNameAsString == null) 
                return base.SelectController(request);
            
            //get the currently cached default controllers - this will not contain duplicate controllers found so if
            // this controller is found in the underlying cache we don't need to do anything
            var map = base.GetControllerMapping();
            if (map.ContainsKey(controllerNameAsString)) 
                return base.SelectController(request);
            
            //the cache does not contain this controller because it's most likely a duplicate, 
            // so we need to sort this out ourselves and we can only do that if the namespace token
            // is formatted correctly.
            var namespaces = routeData.Route.DataTokens["Namespaces"] as IEnumerable<string>;
            if (namespaces == null)
                return base.SelectController(request);

            //see if this is in our cache
            var found = _duplicateControllerTypes.Value.FirstOrDefault(x => string.Equals(x.ControllerName, controllerNameAsString, StringComparison.OrdinalIgnoreCase) && namespaces.Contains(x.ControllerNamespace));
            if (found == null)
                return base.SelectController(request);

            return found.Descriptor;
        }

        private ConcurrentStack<NamespaceHttpControllerMetadata> GetDuplicateControllerTypes()
        {
            var assembliesResolver = _configuration.Services.GetAssembliesResolver();
            var controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
            var controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);

            var groupedByName = controllerTypes.GroupBy(
                t => t.Name.Substring(0, t.Name.Length - ControllerSuffix.Length),
                StringComparer.OrdinalIgnoreCase).Where(x => x.Count() > 1);

            var duplicateControllers = groupedByName.ToDictionary(
                g => g.Key,
                g => g.ToLookup(t => t.Namespace ?? String.Empty, StringComparer.OrdinalIgnoreCase),
                StringComparer.OrdinalIgnoreCase);

            var result = new ConcurrentStack<NamespaceHttpControllerMetadata>();

            foreach (var controllerTypeGroup in duplicateControllers)
            {
                foreach (var controllerType in controllerTypeGroup.Value.SelectMany(controllerTypesGrouping => controllerTypesGrouping))
                {
                    result.Push(new NamespaceHttpControllerMetadata(controllerTypeGroup.Key, controllerType.Namespace,
                        new HttpControllerDescriptor(_configuration, controllerTypeGroup.Key, controllerType)));
                }
            }

            return result;
        }

        private class NamespaceHttpControllerMetadata
        {
            private readonly string _controllerName;
            private readonly string _controllerNamespace;
            private readonly HttpControllerDescriptor _descriptor;

            public NamespaceHttpControllerMetadata(string controllerName, string controllerNamespace, HttpControllerDescriptor descriptor)
            {
                _controllerName = controllerName;
                _controllerNamespace = controllerNamespace;
                _descriptor = descriptor;
            }

            public string ControllerName
            {
                get { return _controllerName; }
            }

            public string ControllerNamespace
            {
                get { return _controllerNamespace; }
            }

            public HttpControllerDescriptor Descriptor
            {
                get { return _descriptor; }
            }
        }
    }
}