using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;

namespace GB5Shared.Middleware;

public static class GatewayPrefixMiddlewareExtensions
{
    /// <summary>
    /// When a Host is reached through the GB5Build gateway under a module alias (e.g. /crm/, /prs/),
    /// the gateway strips that prefix before forwarding but sends it back via the X-GB5-Gateway-Prefix
    /// header. Setting it as PathBase here lets the app still generate correct self-referencing URLs
    /// (e.g. Swagger's swagger.json link) — this affects only URL *generation*, not endpoint routing
    /// (FastEndpoints matches on Request.Path, which is untouched), so real API calls are unaffected.
    /// Direct port access has no such header, so PathBase stays empty and behavior is unchanged.
    /// Note: the standard "X-Forwarded-Prefix" name doesn't work here — YARP treats the X-Forwarded-*
    /// family as reserved and silently strips any such header not set through its own mechanism.
    /// </summary>
    public static IApplicationBuilder UseGatewayPrefixForwarding(this IApplicationBuilder app)
    {
        return app.Use((context, next) =>
        {
            if (context.Request.Headers.TryGetValue("X-GB5-Gateway-Prefix", out var prefix) && !string.IsNullOrEmpty(prefix))
                context.Request.PathBase = new PathString(prefix.ToString());
            return next();
        });
    }
}