import { createHash, randomUUID } from "node:crypto";

/**
 * Derive a stable 12-hex agent id from the FULL session id.
 * Hashing matters: pi session ids are time-ordered UUIDs whose leading chars encode a
 * timestamp, so any prefix collides for sessions launched in the same instant (e.g. cmux
 * opening several panes at once). A hash spreads the random bits across the whole id.
 * Stable across resume: same session id ⇒ same agent id.
 */
export function deriveSelfId(sessionId: string | undefined | null): string {
	if (sessionId && typeof sessionId === "string" && sessionId.trim()) {
		return createHash("sha1").update(sessionId).digest("hex").slice(0, 12);
	}
	return randomUUID().replace(/-/g, "").slice(0, 12); // ephemeral (--no-session) fallback
}