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

public class NamespaceHttpControllerSelector : DefaultHttpControllerSelector
{
    private readonly HttpConfiguration _configuration;
    private readonly Lazy<Dictionary<string, HttpControllerDescriptor>> _controllers;

    public NamespaceHttpControllerSelector(HttpConfiguration configuration) : base(configuration)
    {
        _configuration = configuration;
        _controllers = new Lazy<Dictionary<string, HttpControllerDescriptor>>(InitializeControllerDictionary);
    }

    private Dictionary<string, HttpControllerDescriptor> InitializeControllerDictionary()
    {
        var dictionary = new Dictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);

        var assembliesResolver = _configuration.Services.GetAssembliesResolver();
        var controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();

        var controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);

        foreach (var type in controllerTypes)
        {
            var segments = type.Namespace?.Split(Type.Delimiter);
            var key = String.Format("{0}.{1}", segments.LastOrDefault(), type.Name.Remove(type.Name.Length - "Controller".Length));

            if (!dictionary.Keys.Contains(key))
            {
                dictionary[key] = new HttpControllerDescriptor(_configuration, type.Name, type);
            }
        }

        return dictionary;
    }

    public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
    {
        var routeData = request.GetRouteData();
        var controllerName = routeData.Values["controller"].ToString();
        var namespaceName = routeData.Values["namespace"]?.ToString();
        var key = String.Format("{0}.{1}", namespaceName, controllerName);

        if (_controllers.Value.TryGetValue(key, out var descriptor))
        {
            return descriptor;
        }

        return null;
    }
}