using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Marechai.Database.Models;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Extensions.Logging;

namespace Marechai.Areas.Identity.Pages.Account.Manage
{
    public class EnableAuthenticatorModel : PageModel
    {
        const    string AuthenticatorUriFormat = "otpauth://totp/{0}:{1}?secret={2}&issuer={0}&digits=6";
        readonly ILogger<EnableAuthenticatorModel> _logger;
        readonly UrlEncoder _urlEncoder;
        readonly UserManager<ApplicationUser> _userManager;

        public EnableAuthenticatorModel(UserManager<ApplicationUser> userManager,
                                        ILogger<EnableAuthenticatorModel> logger, UrlEncoder urlEncoder)
        {
            _userManager = userManager;
            _logger      = logger;
            _urlEncoder  = urlEncoder;
        }

        public string SharedKey { get; set; }

        public string AuthenticatorUri { get; set; }

        [TempData]
        public string[] RecoveryCodes { get; set; }

        [TempData]
        public string StatusMessage { get; set; }

        [BindProperty]
        public InputModel Input { get; set; }

        public async Task<IActionResult> OnGetAsync()
        {
            ApplicationUser user = await _userManager.GetUserAsync(User);

            if(user == null)
            {
                return NotFound($"Unable to load user with ID '{_userManager.GetUserId(User)}'.");
            }

            await LoadSharedKeyAndQrCodeUriAsync(user);

            return Page();
        }

        public async Task<IActionResult> OnPostAsync()
        {
            ApplicationUser user = await _userManager.GetUserAsync(User);

            if(user == null)
            {
                return NotFound($"Unable to load user with ID '{_userManager.GetUserId(User)}'.");
            }

            if(!ModelState.IsValid)
            {
                await LoadSharedKeyAndQrCodeUriAsync(user);

                return Page();
            }

            // Strip spaces and hypens
            string verificationCode = Input.Code.Replace(" ", string.Empty).Replace("-", string.Empty);

            bool is2faTokenValid =
                await _userManager.VerifyTwoFactorTokenAsync(user,
                                                             _userManager.Options.Tokens.AuthenticatorTokenProvider,
                                                             verificationCode);

            if(!is2faTokenValid)
            {
                ModelState.AddModelError("Input.Code", "Verification code is invalid.");
                await LoadSharedKeyAndQrCodeUriAsync(user);

                return Page();
            }

            await _userManager.SetTwoFactorEnabledAsync(user, true);
            string userId = await _userManager.GetUserIdAsync(user);
            _logger.LogInformation("User with ID '{UserId}' has enabled 2FA with an authenticator app.", userId);

            StatusMessage = "Your authenticator app has been verified.";

            if(await _userManager.CountRecoveryCodesAsync(user) == 0)
            {
                IEnumerable<string> recoveryCodes = await _userManager.GenerateNewTwoFactorRecoveryCodesAsync(user, 10);
                RecoveryCodes = recoveryCodes.ToArray();

                return RedirectToPage("./ShowRecoveryCodes");
            }

            return RedirectToPage("./TwoFactorAuthentication");
        }

        async Task LoadSharedKeyAndQrCodeUriAsync(ApplicationUser user)
        {
            // Load the authenticator key & QR code URI to display on the form
            string unformattedKey = await _userManager.GetAuthenticatorKeyAsync(user);

            if(string.IsNullOrEmpty(unformattedKey))
            {
                await _userManager.ResetAuthenticatorKeyAsync(user);
                unformattedKey = await _userManager.GetAuthenticatorKeyAsync(user);
            }

            SharedKey = FormatKey(unformattedKey);

            string email = await _userManager.GetEmailAsync(user);
            AuthenticatorUri = GenerateQrCodeUri(email, unformattedKey);
        }

        string FormatKey(string unformattedKey)
        {
            var result          = new StringBuilder();
            int currentPosition = 0;

            while(currentPosition + 4 < unformattedKey.Length)
            {
                result.Append(unformattedKey.Substring(currentPosition, 4)).Append(" ");
                currentPosition += 4;
            }

            if(currentPosition < unformattedKey.Length)
            {
                result.Append(unformattedKey.Substring(currentPosition));
            }

            return result.ToString().ToLowerInvariant();
        }

        string GenerateQrCodeUri(string email, string unformattedKey) =>
            string.Format(AuthenticatorUriFormat, _urlEncoder.Encode("Marechai"), _urlEncoder.Encode(email),
                          unformattedKey);

        public class InputModel
        {
            [Required,
             StringLength(7, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.",
                          MinimumLength   = 6), DataType(DataType.Text), Display(Name = "Verification Code")]
            public string Code { get; set; }
        }
    }
}