using System.Net;
using System.Security.Claims;
using Application.Abstractions.RateLimit;

namespace Web.Api.Middleware;

/// <summary>
/// /v1/* 공개 API endpoint 의 rate limit 미들웨어.
/// 기본 60 req/min per token. 토큰이 없으면 IP 단위.
/// </summary>
public sealed class RateLimitMiddleware(RequestDelegate next, IRateLimiter limiter)
{
    private const int DefaultLimitPerMinute = 60;
    private static readonly TimeSpan Window = TimeSpan.FromMinutes(1);

    public async Task InvokeAsync(HttpContext context)
    {
        if (!context.Request.Path.StartsWithSegments("/v1"))
        {
            await next(context);
            return;
        }

        var key = ResolveKey(context);
        var result = await limiter.CheckAsync(key, DefaultLimitPerMinute, Window, context.RequestAborted);

        context.Response.Headers["X-RateLimit-Limit"] = result.Limit.ToString();
        context.Response.Headers["X-RateLimit-Remaining"] = result.Remaining.ToString();
        context.Response.Headers["X-RateLimit-Reset"] = new DateTimeOffset(result.ResetAt, TimeSpan.Zero).ToUnixTimeSeconds().ToString();

        if (!result.Allowed)
        {
            context.Response.StatusCode = (int)HttpStatusCode.TooManyRequests;
            context.Response.ContentType = "application/problem+json";
            await context.Response.WriteAsJsonAsync(new
            {
                type = "https://tools.ietf.org/html/rfc6585#section-4",
                title = "Too Many Requests",
                status = 429,
                detail = "Rate limit exceeded. Try again later."
            }, context.RequestAborted);
            return;
        }

        await next(context);
    }

    private static string ResolveKey(HttpContext context)
    {
        if (context.User.Identity?.IsAuthenticated == true)
        {
            var tokenID = context.User.FindFirst("token_id")?.Value;
            if (!string.IsNullOrEmpty(tokenID))
            {
                return $"tok:{tokenID}";
            }

            var sub = context.User.FindFirst(ClaimTypes.NameIdentifier)?.Value
                ?? context.User.FindFirst("sub")?.Value;
            if (!string.IsNullOrEmpty(sub))
            {
                return $"sub:{sub}";
            }
        }

        var ip = context.Connection.RemoteIpAddress?.ToString() ?? "unknown";
        return $"ip:{ip}";
    }
}