// This class is derived from https://raw.githubusercontent.com/dotnet/aspnetcore/main/src/Identity/Core/src/IdentityApiEndpointRouteBuilderExtensions.cs
// It was recommended by a member of the .Net platform team to copy this class if I want to customize some of the default behavior.
// That recommendation is here: https://github.com/dotnet/aspnetcore/issues/50303#issuecomment-1836909245

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

namespace Shogi.Api.Controllers;

/// <summary>
/// Provides extension methods for <see cref="IEndpointRouteBuilder"/> to add identity endpoints.
/// </summary>
public static class MyIdentityApiEndpointRouteBuilderExtensions
{
	// Validate the email address using DataAnnotations like the UserValidator does when RequireUniqueEmail = true.
	private static readonly EmailAddressAttribute _emailAddressAttribute = new();

	/// <summary>
	/// Add endpoints for registering, logging in, and logging out using ASP.NET Core Identity.
	/// </summary>
	/// <typeparam name="TUser">The type describing the user. This should match the generic parameter in <see cref="UserManager{TUser}"/>.</typeparam>
	/// <param name="endpoints">
	/// The <see cref="IEndpointRouteBuilder"/> to add the identity endpoints to.
	/// Call <see cref="EndpointRouteBuilderExtensions.MapGroup(IEndpointRouteBuilder, string)"/> to add a prefix to all the endpoints.
	/// </param>
	/// <returns>An <see cref="IEndpointConventionBuilder"/> to further customize the added endpoints.</returns>
	public static IEndpointConventionBuilder MyMapIdentityApi<TUser>(this IEndpointRouteBuilder endpoints, IWebHostEnvironment environment)
			where TUser : class, new()
	{
		ArgumentNullException.ThrowIfNull(endpoints);

		var timeProvider = endpoints.ServiceProvider.GetRequiredService<TimeProvider>();
		var bearerTokenOptions = endpoints.ServiceProvider.GetRequiredService<IOptionsMonitor<BearerTokenOptions>>();
		var emailSender = endpoints.ServiceProvider.GetRequiredService<IEmailSender<TUser>>();
		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("");

		// NOTE: We cannot inject UserManager<TUser> directly because the TUser generic parameter is currently unsupported by RDG.
		// https://github.com/dotnet/aspnetcore/issues/47338
		routeGroup.MapPost("/register", async Task<Results<Ok, ValidationProblem>>
				([FromBody] RegisterRequest registration, HttpContext context, [FromServices] IServiceProvider sp) =>
		{
			var userManager = sp.GetRequiredService<UserManager<TUser>>();

			if (!userManager.SupportsUserEmail)
			{
				throw new NotSupportedException($"{nameof(MyMapIdentityApi)} requires a user store with email support.");
			}

			var userStore = sp.GetRequiredService<IUserStore<TUser>>();
			var emailStore = (IUserEmailStore<TUser>)userStore;
			var email = registration.Email;

			if (string.IsNullOrEmpty(email) || !_emailAddressAttribute.IsValid(email))
			{
				return CreateValidationProblem(IdentityResult.Failed(userManager.ErrorDescriber.InvalidEmail(email)));
			}

			var user = new TUser();
			await userStore.SetUserNameAsync(user, email, CancellationToken.None);
			await emailStore.SetEmailAsync(user, email, CancellationToken.None);
			var result = await userManager.CreateAsync(user, registration.Password);

			if (!result.Succeeded)
			{
				return CreateValidationProblem(result);
			}

			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<TUser>>();

			var useCookieScheme = (useCookies == true) || (useSessionCookies == true);
			var isPersistent = (useCookies == true) && (useSessionCookies != true);
			signInManager.AuthenticationScheme = useCookieScheme ? IdentityConstants.ApplicationScheme : IdentityConstants.BearerScheme;

			var result = await signInManager.PasswordSignInAsync(login.Email, 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<TUser>>();
			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 TUser 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<TUser>>();
			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
			{
				// As with Identity UI, email and user name are one and the same. So when we update the email,
				// we need to update the user name.
				result = await userManager.ChangeEmailAsync(user, changedEmail, code);

				if (result.Succeeded)
				{
					result = await userManager.SetUserNameAsync(user, changedEmail);
				}
			}

			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(MyMapIdentityApi)}-{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<TUser>>();
			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<TUser>>();
			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<TUser>>();

			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<TUser>>();
			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.");
				}
				else 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.");
				}
				else 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<TUser>>();
			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<TUser>>();
			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));
		});

		async Task SendConfirmationEmailAsync(TUser user, UserManager<TUser> 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);
			}

			HostString? host = environment.IsDevelopment() ? null : new HostString("api.lucaserver.space/Shogi.Api");
			var confirmEmailUrl = linkGenerator.GetUriByName(context, confirmEmailEndpointName, routeValues, host: host)
					?? 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;
	}
}