using System.Text;
using MediatR;
using Web.Api.Common;
using Web.Api.Extensions;

namespace Web.Api.Endpoints.OAuth;

/// <summary>
/// POST /oauth/token — RFC 6749 §4.4 Client Credentials grant.
/// Body: application/x-www-form-urlencoded (grant_type, client_id, client_secret, scope)
/// 또는 HTTP Basic auth (Authorization: Basic base64(client_id:client_secret)) + form 의 grant_type/scope.
/// </summary>
internal sealed class Token : IEndpoint
{
    public void MapEndpoint(IEndpointRouteBuilder app)
    {
        app.MapPost("oauth/token", async (
            HttpContext httpContext,
            ISender sender,
            CancellationToken ct
        ) => {
            if (!httpContext.Request.HasFormContentType)
            {
                return CustomResults.Problem(SharedKernel.Results.Result.Failure(SharedKernel.Results.Error.Problem("OAuth.InvalidRequest", "Content-Type must be application/x-www-form-urlencoded.")));
            }

            var form = await httpContext.Request.ReadFormAsync(ct);

            string? clientID = form["client_id"];
            string? clientSecret = form["client_secret"];

            // HTTP Basic auth fallback (RFC 6749 §2.3.1)
            if (string.IsNullOrEmpty(clientID))
            {
                var auth = httpContext.Request.Headers.Authorization.ToString();

                if (auth.StartsWith("Basic ", StringComparison.OrdinalIgnoreCase))
                {
                    try
                    {
                        var base64 = auth["Basic ".Length..];
                        var decoded = Encoding.UTF8.GetString(Convert.FromBase64String(base64));
                        var sep = decoded.IndexOf(':');

                        if (sep > 0)
                        {
                            clientID = decoded[..sep];
                            clientSecret = decoded[(sep + 1)..];
                        }
                    }
                    catch (FormatException)
                    {
                        // ignore — invalid base64 falls through to validation
                    }
                }
            }

            var command = new Application.Features.Api.OAuth.IssueToken.Command(
                form["grant_type"].ToString(),
                clientID,
                clientSecret,
                form["scope"].ToString()
            );

            var result = await sender.Send(command, ct);

            return result.Match(
                data => Results.Ok(data),
                CustomResults.Problem
            );
        })
        .WithTags("OAuth")
        .WithGroupName("public")
        .AllowAnonymous();
    }
}