import type { Context } from "hono";

const LOOPBACK = /^(127\.|::1$|::ffff:127\.)/;

/**
 * The client's address, for rate limits. The socket peer, unless the peer is loopback: then it is
 * a reverse proxy on the same host (Caddy, as Kepr 2 was deployed), and the address is the
 * rightmost `X-Forwarded-For` entry, the one that proxy appended. Anything to its left came from
 * the client and could be forged, so it is never trusted.
 */
export function clientIp(c: Context): string {
	// Bun passes its server as the env; a test passes a stand-in with the same method.
	const server = c.env as { requestIP?: (request: Request) => { address: string } | null };
	const peer = server?.requestIP?.(c.req.raw)?.address ?? "";
	if (!LOOPBACK.test(peer)) return peer;
	return c.req.header("x-forwarded-for")?.split(",").at(-1)?.trim() || peer;
}