// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.ComponentModel.DataAnnotations;
using System.Diagnostics.CodeAnalysis;
using System.Security.Claims;
using System.Text;
using System.Text.Encodings.Web;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.WebUtilities;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNetCore.Identity.UI.V4.Pages.Account.Internal;

/// <summary>
///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
///     directly from your code. This API may change or be removed in future releases.
/// </summary>
[AllowAnonymous]
[IdentityDefaultUI(typeof(ExternalLoginModel<>))]
public class ExternalLoginModel : PageModel
{
    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    [BindProperty]
    public InputModel Input { get; set; } = default!;

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public string? ProviderDisplayName { get; set; }

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public string? ReturnUrl { get; set; }

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    [TempData]
    public string? ErrorMessage { get; set; }

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public class InputModel
    {
        /// <summary>
        ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
        ///     directly from your code. This API may change or be removed in future releases.
        /// </summary>
        [Required]
        [EmailAddress]
        public string Email { get; set; } = default!;
    }

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public virtual IActionResult OnGet() => throw new NotImplementedException();

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public virtual IActionResult OnPost(string provider, [StringSyntax(StringSyntaxAttribute.Uri)] string? returnUrl = null) => throw new NotImplementedException();

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public virtual Task<IActionResult> OnGetCallbackAsync([StringSyntax(StringSyntaxAttribute.Uri)] string? returnUrl = null, string? remoteError = null) => throw new NotImplementedException();

    /// <summary>
    ///     This API supports the ASP.NET Core Identity default UI infrastructure and is not intended to be used
    ///     directly from your code. This API may change or be removed in future releases.
    /// </summary>
    public virtual Task<IActionResult> OnPostConfirmationAsync([StringSyntax(StringSyntaxAttribute.Uri)] string? returnUrl = null) => throw new NotImplementedException();
}

internal sealed class ExternalLoginModel<TUser> : ExternalLoginModel where TUser : class
{
    private readonly SignInManager<TUser> _signInManager;
    private readonly UserManager<TUser> _userManager;
    private readonly IUserStore<TUser> _userStore;
    private readonly IUserEmailStore<TUser> _emailStore;
    private readonly IEmailSender<TUser> _emailSender;
    private readonly ILogger<ExternalLoginModel> _logger;

    public ExternalLoginModel(
        SignInManager<TUser> signInManager,
        UserManager<TUser> userManager,
        IUserStore<TUser> userStore,
        ILogger<ExternalLoginModel> logger,
        IEmailSender<TUser> emailSender)
    {
        _signInManager = signInManager;
        _userManager = userManager;
        _userStore = userStore;
        _emailStore = GetEmailStore();
        _logger = logger;
        _emailSender = emailSender;
    }

    public override IActionResult OnGet() => RedirectToPage("./Login");

    public override IActionResult OnPost(string provider, string? returnUrl = null)
    {
        // Request a redirect to the external login provider.
        var redirectUrl = Url.Page("./ExternalLogin", pageHandler: "Callback", values: new { returnUrl });
        var properties = _signInManager.ConfigureExternalAuthenticationProperties(provider, redirectUrl);
        return new ChallengeResult(provider, properties);
    }

    public override async Task<IActionResult> OnGetCallbackAsync(string? returnUrl = null, string? remoteError = null)
    {
        returnUrl = returnUrl ?? Url.Content("~/");
        if (remoteError != null)
        {
            ErrorMessage = $"Error from external provider: {remoteError}";
            return RedirectToPage("./Login", new { ReturnUrl = returnUrl });
        }
        var info = await _signInManager.GetExternalLoginInfoAsync();
        if (info == null)
        {
            ErrorMessage = "Error loading external login information.";
            return RedirectToPage("./Login", new { ReturnUrl = returnUrl });
        }

        // Sign in the user with this external login provider if the user already has a login.
        var result = await _signInManager.ExternalLoginSignInAsync(info.LoginProvider, info.ProviderKey, isPersistent: false, bypassTwoFactor: true);
        if (result.Succeeded)
        {
            if (_logger.IsEnabled(LogLevel.Information))
            {
                _logger.LogInformation(LoggerEventIds.UserLoggedInByExternalProvider, "User logged in with {LoginProvider} provider.", info.LoginProvider);
            }
            return LocalRedirect(returnUrl);
        }
        if (result.IsLockedOut)
        {
            return RedirectToPage("./Lockout");
        }
        else
        {
            // If the user does not have an account, then ask the user to create an account.
            ReturnUrl = returnUrl;
            ProviderDisplayName = info.ProviderDisplayName;
            if (info.Principal!.HasClaim(c => c.Type == ClaimTypes.Email))
            {
                Input = new InputModel
                {
                    Email = info.Principal.FindFirstValue(ClaimTypes.Email)!
                };
            }
            return Page();
        }
    }

    public override async Task<IActionResult> OnPostConfirmationAsync(string? returnUrl = null)
    {
        returnUrl = returnUrl ?? Url.Content("~/");
        // Get the information about the user from the external login provider
        var info = await _signInManager.GetExternalLoginInfoAsync();
        if (info == null)
        {
            ErrorMessage = "Error loading external login information during confirmation.";
            return RedirectToPage("./Login", new { ReturnUrl = returnUrl });
        }

        if (ModelState.IsValid)
        {
            var user = CreateUser();

            await _userStore.SetUserNameAsync(user, Input.Email, CancellationToken.None);
            await _emailStore.SetEmailAsync(user, Input.Email, CancellationToken.None);

            var result = await _userManager.CreateAsync(user);
            if (result.Succeeded)
            {
                result = await _userManager.AddLoginAsync(user, info);
                if (result.Succeeded)
                {
                    if (_logger.IsEnabled(LogLevel.Information))
                    {
                        _logger.LogInformation(LoggerEventIds.UserCreatedByExternalProvider, "User created an account using {Name} provider.", info.LoginProvider);
                    }

                    var userId = await _userManager.GetUserIdAsync(user);
                    var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
                    code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code));
                    var callbackUrl = Url.Page(
                        "/Account/ConfirmEmail",
                        pageHandler: null,
                        values: new { area = "Identity", userId = userId, code = code },
                        protocol: Request.Scheme)!;

                    await _emailSender.SendConfirmationLinkAsync(user, Input.Email, HtmlEncoder.Default.Encode(callbackUrl));

                    // If account confirmation is required, we need to show the link if we don't have a real email sender
                    if (_userManager.Options.SignIn.RequireConfirmedAccount)
                    {
                        return RedirectToPage("./RegisterConfirmation", new { Email = Input.Email });
                    }

                    await _signInManager.SignInAsync(user, isPersistent: false, info.LoginProvider);
                    return LocalRedirect(returnUrl);
                }
            }
            foreach (var error in result.Errors)
            {
                ModelState.AddModelError(string.Empty, error.Description);
            }
        }

        ProviderDisplayName = info.ProviderDisplayName;
        ReturnUrl = returnUrl;
        return Page();
    }

    private TUser CreateUser()
    {
        try
        {
            return Activator.CreateInstance<TUser>();
        }
        catch
        {
            throw new InvalidOperationException($"Can't create an instance of '{nameof(TUser)}'. " +
                $"Ensure that '{nameof(TUser)}' is not an abstract class and has a parameterless constructor, or alternatively " +
                $"override the external login page in /Areas/Identity/Pages/Account/ExternalLogin.cshtml");
        }
    }

    private IUserEmailStore<TUser> GetEmailStore()
    {
        if (!_userManager.SupportsUserEmail)
        {
            throw new NotSupportedException("The default UI requires a user store with email support.");
        }
        return (IUserEmailStore<TUser>)_userStore;
    }
}
