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<IEnumerable<Type>> _duplicateControllerTypes;

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

        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            var routeData = request.GetRouteData();
            if (routeData == null || routeData.Route == 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
                .Where(x => string.Equals(x.Name, controllerNameAsString + ControllerSuffix, StringComparison.OrdinalIgnoreCase))
                .FirstOrDefault(x => namespaces.Contains(x.Namespace));

            if (found == null)
                return base.SelectController(request);

            return new HttpControllerDescriptor(_configuration, controllerNameAsString, found);
        }

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

            //we have all controller types, so just store the ones with duplicate class names - we don't
            // want to cache too much and the underlying selector caches everything else

            var duplicates = controllerTypes.GroupBy(x => x.Name)
                .Where(x => x.Count() > 1)
                .SelectMany(x => x);

            return duplicates;
        }
        
    }
}