using System.ComponentModel.DataAnnotations;
using System.Diagnostics;
using System.Security.Claims;
using System.Text;
using System.Text.Encodings.Web;
using Abstractions.Entities;
using Abstractions.Services;
using Microsoft.AspNetCore.Authentication.BearerToken;
using Microsoft.AspNetCore.Http.HttpResults;
using Microsoft.AspNetCore.Http.Metadata;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.Data;
using Microsoft.AspNetCore.WebUtilities;
using Microsoft.Extensions.Options;
using System.Text.RegularExpressions;

namespace Server.Authentication;

public static class AuthEndpoints
{
    // Validate the email address using DataAnnotations like the UserValidator does when RequireUniqueEmail = true.
    private static readonly EmailAddressAttribute EmailAddressAttribute = new();

    // Mirrors the client-side pin validation in register.vue: exactly 4 digits.
    private static readonly Regex PinFormat = new("^\\d{4}$", RegexOptions.Compiled);

    public static IEndpointConventionBuilder MapIdentityApi(this IEndpointRouteBuilder endpoints)
    {
        ArgumentNullException.ThrowIfNull(endpoints);
 
        var timeProvider = endpoints.ServiceProvider.GetRequiredService<TimeProvider>();
        var bearerTokenOptions = endpoints.ServiceProvider.GetRequiredService<IOptionsMonitor<BearerTokenOptions>>();
        var emailSender = endpoints.ServiceProvider.GetRequiredService<IEmailSender<User>>();
        var linkGenerator = endpoints.ServiceProvider.GetRequiredService<LinkGenerator>();
 
        // We'll figure out a unique endpoint name based on the final route pattern during endpoint generation.
        string? confirmEmailEndpointName = null;
 
        var routeGroup = endpoints.MapGroup("/auth");

        routeGroup.MapPost("/register", async Task<Results<Ok, ValidationProblem>>
            ([FromBody] Models.Request.RegisterRequest registration, HttpContext context, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            var signinManager = sp.GetRequiredService<SignInManager<User>>();
            var userService = sp.GetRequiredService<IUserService>();
            var cardService = sp.GetRequiredService<ICardService>();

            if (!userManager.SupportsUserEmail)
            {
                throw new NotSupportedException($"{nameof(MapIdentityApi)} requires a user store with email support.");
            }
 
            var userStore = sp.GetRequiredService<IUserStore<User>>();
            var emailStore = (IUserEmailStore<User>)userStore;
            var email = registration.Email;
 
            if (string.IsNullOrEmpty(email) || !EmailAddressAttribute.IsValid(email))
            {
                return CreateValidationProblem(IdentityResult.Failed(userManager.ErrorDescriber.InvalidEmail(email)));
            }

            var validCard = await cardService.ValidatePinAsync(registration.KonamiId, registration.Pin);

            if (!validCard)
            {
                return CreateValidationProblem("InvalidCard",
                    "The provided Card is invalid");
            }

            var user = await userService.GetUserByKonamiId(registration.KonamiId);

            if (user == null)
            {
                return CreateValidationProblem("InvalidKonamiId",
                    "The provided Card is not found");
            }

            await userStore.SetUserNameAsync(user, registration.Username, CancellationToken.None);
            await emailStore.SetEmailAsync(user, email, CancellationToken.None);
            var result = await userManager.UpdateAsync(user);
 
            if (!result.Succeeded)
            {
                return CreateValidationProblem(result);
            }

            result = await userManager.AddPasswordAsync(user, registration.Password);

            await SendConfirmationEmailAsync(user, userManager, context, email);
            return TypedResults.Ok();
        });
        
        routeGroup.MapPost("/login", async Task<Results<Ok<AccessTokenResponse>, EmptyHttpResult, ProblemHttpResult>>
            ([FromBody] LoginRequest login, [FromQuery] bool? useCookies, [FromQuery] bool? useSessionCookies, [FromServices] IServiceProvider sp) =>
        {
            var signInManager = sp.GetRequiredService<SignInManager<User>>();
 
            var useCookieScheme = (useCookies == true) || (useSessionCookies == true);
            var isPersistent = (useCookies == true) && (useSessionCookies != true);
            signInManager.AuthenticationScheme = useCookieScheme ? IdentityConstants.ApplicationScheme : IdentityConstants.BearerScheme;
 
            var user = await signInManager.UserManager.FindByEmailAsync(login.Email);
            user ??= await signInManager.UserManager.FindByNameAsync(login.Email);

            if (user == null)
            {
                return TypedResults.Problem("Invalid login attempt.", statusCode: StatusCodes.Status401Unauthorized);
            }

            var result = await signInManager.PasswordSignInAsync(user!.UserName!, login.Password, isPersistent, lockoutOnFailure: true);

            if (result.RequiresTwoFactor)
            {
                if (!string.IsNullOrEmpty(login.TwoFactorCode))
                {
                    result = await signInManager.TwoFactorAuthenticatorSignInAsync(login.TwoFactorCode, isPersistent, rememberClient: isPersistent);
                }
                else if (!string.IsNullOrEmpty(login.TwoFactorRecoveryCode))
                {
                    result = await signInManager.TwoFactorRecoveryCodeSignInAsync(login.TwoFactorRecoveryCode);
                }
            }
 
            if (!result.Succeeded)
            {
                return TypedResults.Problem(result.ToString(), statusCode: StatusCodes.Status401Unauthorized);
            }
 
            // The signInManager already produced the needed response in the form of a cookie or bearer token.
            return TypedResults.Empty;
        });
 
        routeGroup.MapPost("/refresh", async Task<Results<Ok<AccessTokenResponse>, UnauthorizedHttpResult, SignInHttpResult, ChallengeHttpResult>>
            ([FromBody] RefreshRequest refreshRequest, [FromServices] IServiceProvider sp) =>
        {
            var signInManager = sp.GetRequiredService<SignInManager<User>>();
            var refreshTokenProtector = bearerTokenOptions.Get(IdentityConstants.BearerScheme).RefreshTokenProtector;
            var refreshTicket = refreshTokenProtector.Unprotect(refreshRequest.RefreshToken);
 
            // Reject the /refresh attempt with a 401 if the token expired or the security stamp validation fails
            if (refreshTicket?.Properties.ExpiresUtc is not { } expiresUtc ||
                timeProvider.GetUtcNow() >= expiresUtc ||
                await signInManager.ValidateSecurityStampAsync(refreshTicket.Principal) is not { } user)
 
            {
                return TypedResults.Challenge();
            }
 
            var newPrincipal = await signInManager.CreateUserPrincipalAsync(user);
            return TypedResults.SignIn(newPrincipal, authenticationScheme: IdentityConstants.BearerScheme);
        });
 
        routeGroup.MapGet("/confirmEmail", async Task<Results<ContentHttpResult, UnauthorizedHttpResult>>
            ([FromQuery] string userId, [FromQuery] string code, [FromQuery] string? changedEmail, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.FindByIdAsync(userId) is not { } user)
            {
                // We could respond with a 404 instead of a 401 like Identity UI, but that feels like unnecessary information.
                return TypedResults.Unauthorized();
            }
 
            try
            {
                code = Encoding.UTF8.GetString(WebEncoders.Base64UrlDecode(code));
            }
            catch (FormatException)
            {
                return TypedResults.Unauthorized();
            }
 
            IdentityResult result;
 
            if (string.IsNullOrEmpty(changedEmail))
            {
                result = await userManager.ConfirmEmailAsync(user, code);
            }
            else
            {
                // Unlike Identity UI's default assumption, username and email are
                // independent here (registration collects them separately, and
                // Settings lets either be changed on its own) — so confirming a
                // changed email must not also overwrite the username.
                result = await userManager.ChangeEmailAsync(user, changedEmail, code);
            }
 
            if (!result.Succeeded)
            {
                return TypedResults.Unauthorized();
            }
 
            return TypedResults.Text("Thank you for confirming your email.");
        })
        .Add(endpointBuilder =>
        {
            var finalPattern = ((RouteEndpointBuilder)endpointBuilder).RoutePattern.RawText;
            confirmEmailEndpointName = $"{nameof(MapIdentityApi)}-{finalPattern}";
            endpointBuilder.Metadata.Add(new EndpointNameMetadata(confirmEmailEndpointName));
        });
 
        routeGroup.MapPost("/resendConfirmationEmail", async Task<Ok>
            ([FromBody] ResendConfirmationEmailRequest resendRequest, HttpContext context, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.FindByEmailAsync(resendRequest.Email) is not { } user)
            {
                return TypedResults.Ok();
            }
 
            await SendConfirmationEmailAsync(user, userManager, context, resendRequest.Email);
            return TypedResults.Ok();
        });
 
        routeGroup.MapPost("/forgotPassword", async Task<Results<Ok, ValidationProblem>>
            ([FromBody] ForgotPasswordRequest resetRequest, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            var user = await userManager.FindByEmailAsync(resetRequest.Email);
 
            if (user is not null && await userManager.IsEmailConfirmedAsync(user))
            {
                var code = await userManager.GeneratePasswordResetTokenAsync(user);
                code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code));
 
                await emailSender.SendPasswordResetCodeAsync(user, resetRequest.Email, HtmlEncoder.Default.Encode(code));
            }
 
            // Don't reveal that the user does not exist or is not confirmed, so don't return a 200 if we would have
            // returned a 400 for an invalid code given a valid user email.
            return TypedResults.Ok();
        });
 
        routeGroup.MapPost("/resetPassword", async Task<Results<Ok, ValidationProblem>>
            ([FromBody] ResetPasswordRequest resetRequest, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
 
            var user = await userManager.FindByEmailAsync(resetRequest.Email);
 
            if (user is null || !(await userManager.IsEmailConfirmedAsync(user)))
            {
                // Don't reveal that the user does not exist or is not confirmed, so don't return a 200 if we would have
                // returned a 400 for an invalid code given a valid user email.
                return CreateValidationProblem(IdentityResult.Failed(userManager.ErrorDescriber.InvalidToken()));
            }
 
            IdentityResult result;
            try
            {
                var code = Encoding.UTF8.GetString(WebEncoders.Base64UrlDecode(resetRequest.ResetCode));
                result = await userManager.ResetPasswordAsync(user, code, resetRequest.NewPassword);
            }
            catch (FormatException)
            {
                result = IdentityResult.Failed(userManager.ErrorDescriber.InvalidToken());
            }
 
            if (!result.Succeeded)
            {
                return CreateValidationProblem(result);
            }
 
            return TypedResults.Ok();
        });
 
        var accountGroup = routeGroup.MapGroup("/manage").RequireAuthorization();
 
        accountGroup.MapPost("/2fa", async Task<Results<Ok<TwoFactorResponse>, ValidationProblem, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromBody] TwoFactorRequest tfaRequest, [FromServices] IServiceProvider sp) =>
        {
            var signInManager = sp.GetRequiredService<SignInManager<User>>();
            var userManager = signInManager.UserManager;
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }
 
            if (tfaRequest.Enable == true)
            {
                if (tfaRequest.ResetSharedKey)
                {
                    return CreateValidationProblem("CannotResetSharedKeyAndEnable",
                        "Resetting the 2fa shared key must disable 2fa until a 2fa token based on the new shared key is validated.");
                }
 
                if (string.IsNullOrEmpty(tfaRequest.TwoFactorCode))
                {
                    return CreateValidationProblem("RequiresTwoFactor",
                        "No 2fa token was provided by the request. A valid 2fa token is required to enable 2fa.");
                }
 
                if (!await userManager.VerifyTwoFactorTokenAsync(user, userManager.Options.Tokens.AuthenticatorTokenProvider, tfaRequest.TwoFactorCode))
                {
                    return CreateValidationProblem("InvalidTwoFactorCode",
                        "The 2fa token provided by the request was invalid. A valid 2fa token is required to enable 2fa.");
                }
 
                await userManager.SetTwoFactorEnabledAsync(user, true);
            }
            else if (tfaRequest.Enable == false || tfaRequest.ResetSharedKey)
            {
                await userManager.SetTwoFactorEnabledAsync(user, false);
            }
 
            if (tfaRequest.ResetSharedKey)
            {
                await userManager.ResetAuthenticatorKeyAsync(user);
            }
 
            string[]? recoveryCodes = null;
            if (tfaRequest.ResetRecoveryCodes || (tfaRequest.Enable == true && await userManager.CountRecoveryCodesAsync(user) == 0))
            {
                var recoveryCodesEnumerable = await userManager.GenerateNewTwoFactorRecoveryCodesAsync(user, 10);
                recoveryCodes = recoveryCodesEnumerable?.ToArray();
            }
 
            if (tfaRequest.ForgetMachine)
            {
                await signInManager.ForgetTwoFactorClientAsync();
            }
 
            var key = await userManager.GetAuthenticatorKeyAsync(user);
            if (string.IsNullOrEmpty(key))
            {
                await userManager.ResetAuthenticatorKeyAsync(user);
                key = await userManager.GetAuthenticatorKeyAsync(user);
 
                if (string.IsNullOrEmpty(key))
                {
                    throw new NotSupportedException("The user manager must produce an authenticator key after reset.");
                }
            }
 
            return TypedResults.Ok(new TwoFactorResponse
            {
                SharedKey = key,
                RecoveryCodes = recoveryCodes,
                RecoveryCodesLeft = recoveryCodes?.Length ?? await userManager.CountRecoveryCodesAsync(user),
                IsTwoFactorEnabled = await userManager.GetTwoFactorEnabledAsync(user),
                IsMachineRemembered = await signInManager.IsTwoFactorClientRememberedAsync(user),
            });
        });
 
        accountGroup.MapGet("/info", async Task<Results<Ok<InfoResponse>, ValidationProblem, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }
 
            return TypedResults.Ok(await CreateInfoResponseAsync(user, userManager));
        });
 
        accountGroup.MapPost("/info", async Task<Results<Ok<InfoResponse>, ValidationProblem, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromBody] InfoRequest infoRequest, HttpContext context, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }
 
            if (!string.IsNullOrEmpty(infoRequest.NewEmail) && !EmailAddressAttribute.IsValid(infoRequest.NewEmail))
            {
                return CreateValidationProblem(IdentityResult.Failed(userManager.ErrorDescriber.InvalidEmail(infoRequest.NewEmail)));
            }
 
            if (!string.IsNullOrEmpty(infoRequest.NewPassword))
            {
                if (string.IsNullOrEmpty(infoRequest.OldPassword))
                {
                    return CreateValidationProblem("OldPasswordRequired",
                        "The old password is required to set a new password. If the old password is forgotten, use /resetPassword.");
                }
 
                var changePasswordResult = await userManager.ChangePasswordAsync(user, infoRequest.OldPassword, infoRequest.NewPassword);
                if (!changePasswordResult.Succeeded)
                {
                    return CreateValidationProblem(changePasswordResult);
                }
            }
 
            if (!string.IsNullOrEmpty(infoRequest.NewEmail))
            {
                var email = await userManager.GetEmailAsync(user);
 
                if (email != infoRequest.NewEmail)
                {
                    await SendConfirmationEmailAsync(user, userManager, context, infoRequest.NewEmail, isChange: true);
                }
            }
 
            return TypedResults.Ok(await CreateInfoResponseAsync(user, userManager));
        });

        accountGroup.MapPost("/username", async Task<Results<Ok, ValidationProblem, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromBody] Models.Request.UpdateUsernameRequest usernameRequest, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }

            if (string.IsNullOrWhiteSpace(usernameRequest.NewUsername) || usernameRequest.NewUsername.Length < 3)
            {
                return CreateValidationProblem("InvalidUserName",
                    "Username must be at least 3 characters.");
            }

            var result = await userManager.SetUserNameAsync(user, usernameRequest.NewUsername);
            if (!result.Succeeded)
            {
                return CreateValidationProblem(result);
            }

            return TypedResults.Ok();
        });

        accountGroup.MapGet("/pin", async Task<Results<Ok<Models.Response.PinResponse>, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }

            return TypedResults.Ok(new Models.Response.PinResponse { Pin = user.Pin });
        });

        accountGroup.MapPost("/pin", async Task<Results<Ok, ValidationProblem, NotFound>>
            (ClaimsPrincipal claimsPrincipal, [FromBody] Models.Request.UpdatePinRequest pinRequest, [FromServices] IServiceProvider sp) =>
        {
            var userManager = sp.GetRequiredService<UserManager<User>>();
            if (await userManager.GetUserAsync(claimsPrincipal) is not { } user)
            {
                return TypedResults.NotFound();
            }

            if (user.Pin != pinRequest.OldPin)
            {
                return CreateValidationProblem("InvalidPin", "The current pin is incorrect.");
            }

            if (!PinFormat.IsMatch(pinRequest.NewPin))
            {
                return CreateValidationProblem("InvalidPin", "Pin must be exactly 4 digits.");
            }

            user.Pin = pinRequest.NewPin;
            var result = await userManager.UpdateAsync(user);
            if (!result.Succeeded)
            {
                return CreateValidationProblem(result);
            }

            return TypedResults.Ok();
        });

        async Task SendConfirmationEmailAsync(User user, UserManager<User> userManager, HttpContext context, string email, bool isChange = false)
        {
            if (confirmEmailEndpointName is null)
            {
                throw new NotSupportedException("No email confirmation endpoint was registered!");
            }
 
            var code = isChange
                ? await userManager.GenerateChangeEmailTokenAsync(user, email)
                : await userManager.GenerateEmailConfirmationTokenAsync(user);
            code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code));
 
            var userId = await userManager.GetUserIdAsync(user);
            var routeValues = new RouteValueDictionary()
            {
                ["userId"] = userId,
                ["code"] = code,
            };
 
            if (isChange)
            {
                // This is validated by the /confirmEmail endpoint on change.
                routeValues.Add("changedEmail", email);
            }
 
            var confirmEmailUrl = linkGenerator.GetUriByName(context, confirmEmailEndpointName, routeValues)
                ?? throw new NotSupportedException($"Could not find endpoint named '{confirmEmailEndpointName}'.");
 
            await emailSender.SendConfirmationLinkAsync(user, email, HtmlEncoder.Default.Encode(confirmEmailUrl));
        }
 
        return new IdentityEndpointsConventionBuilder(routeGroup);
    }
 
    private static ValidationProblem CreateValidationProblem(string errorCode, string errorDescription) =>
        TypedResults.ValidationProblem(new Dictionary<string, string[]> {
            { errorCode, [errorDescription] }
        });
 
    private static ValidationProblem CreateValidationProblem(IdentityResult result)
    {
        // We expect a single error code and description in the normal case.
        // This could be golfed with GroupBy and ToDictionary, but perf! :P
        Debug.Assert(!result.Succeeded);
        var errorDictionary = new Dictionary<string, string[]>(1);
 
        foreach (var error in result.Errors)
        {
            string[] newDescriptions;
 
            if (errorDictionary.TryGetValue(error.Code, out var descriptions))
            {
                newDescriptions = new string[descriptions.Length + 1];
                Array.Copy(descriptions, newDescriptions, descriptions.Length);
                newDescriptions[descriptions.Length] = error.Description;
            }
            else
            {
                newDescriptions = [error.Description];
            }
 
            errorDictionary[error.Code] = newDescriptions;
        }
 
        return TypedResults.ValidationProblem(errorDictionary);
    }
 
    private static async Task<InfoResponse> CreateInfoResponseAsync<TUser>(TUser user, UserManager<TUser> userManager)
        where TUser : class
    {
        return new()
        {
            Email = await userManager.GetEmailAsync(user) ?? throw new NotSupportedException("Users must have an email."),
            IsEmailConfirmed = await userManager.IsEmailConfirmedAsync(user),
        };
    }
 
    // Wrap RouteGroupBuilder with a non-public type to avoid a potential future behavioral breaking change.
    private sealed class IdentityEndpointsConventionBuilder(RouteGroupBuilder inner) : IEndpointConventionBuilder
    {
        private IEndpointConventionBuilder InnerAsConventionBuilder => inner;
 
        public void Add(Action<EndpointBuilder> convention) => InnerAsConventionBuilder.Add(convention);
        public void Finally(Action<EndpointBuilder> finallyConvention) => InnerAsConventionBuilder.Finally(finallyConvention);
    }
 
    [AttributeUsage(AttributeTargets.Parameter)]
    private sealed class FromBodyAttribute : Attribute, IFromBodyMetadata
    {
    }
 
    [AttributeUsage(AttributeTargets.Parameter)]
    private sealed class FromServicesAttribute : Attribute, IFromServiceMetadata
    {
    }
 
    [AttributeUsage(AttributeTargets.Parameter)]
    private sealed class FromQueryAttribute : Attribute, IFromQueryMetadata
    {
        public string? Name => null;
    }
}