using System.Security.Claims;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Mvc;
using OpenIddict.Abstractions;
using OpenIddict.Client.AspNetCore;
using static OpenIddict.Abstractions.OpenIddictConstants;

namespace OpenIddict.Sandbox.AspNetCore.Server.Controllers;

public class AuthenticationController : Controller
{
    // Note: this controller uses the same callback action for all providers
    // but for users who prefer using a different action per provider,
    // the following action can be split into separate actions.
    [HttpGet("~/callback/login/{provider}"), HttpPost("~/callback/login/{provider}"), IgnoreAntiforgeryToken]
    public async Task<ActionResult> LogInCallback()
    {
        // Retrieve the authorization data validated by OpenIddict as part of the callback handling.
        var result = await HttpContext.AuthenticateAsync(OpenIddictClientAspNetCoreDefaults.AuthenticationScheme);

        // Multiple strategies exist to handle OAuth 2.0/OpenID Connect callbacks, each with their pros and cons:
        //
        //   * Directly using the tokens to perform the necessary action(s) on behalf of the user, which is suitable
        //     for applications that don't need a long-term access to the user's resources or don't want to store
        //     access/refresh tokens in a database or in an authentication cookie (which has security implications).
        //     It is also suitable for applications that don't need to authenticate users but only need to perform
        //     action(s) on their behalf by making API calls using the access token returned by the remote server.
        //
        //   * Storing the external claims/tokens in a database (and optionally keeping the essential claims in an
        //     authentication cookie so that cookie size limits are not hit). For the applications that use ASP.NET
        //     Core Identity, the UserManager.SetAuthenticationTokenAsync() API can be used to store external tokens.
        //
        //     Note: in this case, it's recommended to use column encryption to protect the tokens in the database.
        //
        //   * Storing the external claims/tokens in an authentication cookie, which doesn't require having
        //     a user database but may be affected by the cookie size limits enforced by most browser vendors
        //     (e.g Safari for macOS and Safari for iOS/iPadOS enforce a per-domain 4KB limit for all cookies).
        //
        //     Note: this is the approach used here, but the external claims are first filtered to only persist
        //     a few claims like the user identifier. The same approach is used to store the access/refresh tokens.

        // Important: if the remote server doesn't support OpenID Connect and doesn't expose a userinfo endpoint,
        // result.Principal.Identity will represent an unauthenticated identity and won't contain any user claim.
        //
        // Such identities cannot be used as-is to build an authentication cookie in ASP.NET Core (as the
        // antiforgery stack requires at least a name claim to bind CSRF cookies to the user's identity) but
        // the access/refresh tokens can be retrieved using result.Properties.GetTokens() to make API calls.
        if (result is not { Succeeded: true, Principal.Identity.IsAuthenticated: true })
        {
            throw new InvalidOperationException("The external authorization data cannot be used for authentication.");
        }

        // Build an identity based on the external claims and that will be used to create the authentication cookie.
        var identity = new ClaimsIdentity(
            authenticationType: "ExternalLogin",
            nameType: ClaimTypes.Name,
            roleType: ClaimTypes.Role);

        // By default, OpenIddict will automatically try to map the email/name and name identifier claims from
        // their standard OpenID Connect or provider-specific equivalent, if available. If needed, additional
        // claims can be resolved from the external identity and copied to the final authentication cookie.
        identity.SetClaim(ClaimTypes.Email, result.Principal.GetClaim(ClaimTypes.Email))
                .SetClaim(ClaimTypes.Name, result.Principal.GetClaim(ClaimTypes.Name))
                .SetClaim(ClaimTypes.NameIdentifier, result.Principal.GetClaim(ClaimTypes.NameIdentifier));

        // Preserve the registration details to be able to resolve them later.
        identity.SetClaim(Claims.Private.RegistrationId, result.Principal.GetClaim(Claims.Private.RegistrationId))
                .SetClaim(Claims.Private.ProviderName, result.Principal.GetClaim(Claims.Private.ProviderName));

        // Important: when using ASP.NET Core Identity and its default UI, the identity created in this action is
        // not directly persisted in the final authentication cookie (called "application cookie" by Identity) but
        // in an intermediate authentication cookie called "external cookie" (the final authentication cookie is
        // later created by Identity's ExternalLogin Razor Page by calling SignInManager.ExternalLoginSignInAsync()).
        //
        // Unfortunately, this process doesn't preserve the claims added here, which prevents flowing claims
        // returned by the external provider down to the final authentication cookie. For scenarios that
        // require that, the claims can be stored in Identity's database by calling UserManager.AddClaimAsync()
        // directly in this action or by scaffolding the ExternalLogin.cshtml page that is part of the default UI:
        // https://learn.microsoft.com/en-us/aspnet/core/security/authentication/social/additional-claims#add-and-update-user-claims.
        //
        // Alternatively, if flowing the claims from the "external cookie" to the "application cookie" is preferred,
        // the default ExternalLogin.cshtml page provided by Identity can be scaffolded to replace the call to
        // SignInManager.ExternalLoginSignInAsync() by a manual sign-in operation that will preserve the claims.
        // For scenarios where scaffolding the ExternalLogin.cshtml page is not convenient, a custom SignInManager
        // with an overridden SignInOrTwoFactorAsync() method can also be used to tweak the default Identity logic.
        //
        // For more information, see https://haacked.com/archive/2019/07/16/external-claims/ and
        // https://stackoverflow.com/questions/42660568/asp-net-core-identity-extract-and-save-external-login-tokens-and-add-claims-to-l/42670559#42670559.

        // Build the authentication properties based on the properties that were added when the challenge was triggered.
        var properties = new AuthenticationProperties(result.Properties.Items)
        {
            RedirectUri = result.Properties.RedirectUri ?? "/",

            // Set the creation and expiration dates of the ticket to null to decorrelate the lifetime
            // of the resulting authentication cookie from the lifetime of the identity token returned by
            // the authorization server (if applicable). In this case, the expiration date time will be
            // automatically computed by the cookie handler using the lifetime configured in the options.
            //
            // Applications that prefer binding the lifetime of the ticket stored in the authentication cookie
            // to the identity token returned by the identity provider can remove or comment these two lines:
            IssuedUtc = null,
            ExpiresUtc = null,

            // Note: this flag controls whether the authentication cookie that will be returned to the
            // browser will be treated as a session cookie (i.e destroyed when the browser is closed)
            // or as a persistent cookie. In both cases, the lifetime of the authentication ticket is
            // always stored as protected data, preventing malicious users from trying to use an
            // authentication cookie beyond the lifetime of the authentication ticket itself.
            IsPersistent = false
        };

        // If needed, the tokens returned by the authorization server can be stored in the authentication cookie.
        // To make cookies less heavy, tokens that are not used are filtered out before creating the cookie.
        properties.StoreTokens(result.Properties.GetTokens().Where(token => token.Name is
            // Preserve the access and refresh tokens returned in the token response, if available.
            OpenIddictClientAspNetCoreConstants.Tokens.BackchannelAccessToken or
            OpenIddictClientAspNetCoreConstants.Tokens.RefreshToken));

#if SUPPORTS_REDIRECTION_ON_SIGN_IN
        // Ask the default sign-in handler to return a new cookie and redirect the
        // user agent to the return URL stored in the authentication properties.
        //
        // For scenarios where the default sign-in handler configured in the ASP.NET Core
        // authentication options shouldn't be used, a specific scheme can be specified here.
        return SignIn(new ClaimsPrincipal(identity), properties);
#else
        // Note: "return SignIn(...)" cannot be directly used as-is on ASP.NET Core <7.0, as the cookies handler
        // doesn't allow redirecting from an endpoint that doesn't match the path set in the cookie options.
        await HttpContext.SignInAsync(new ClaimsPrincipal(identity), properties);
        return Redirect(properties.RedirectUri ?? "/");
#endif
    }
}