"use client";
import { ClientApiError } from "@/lib/client/api";

/** POST /api/arena/:id/export?format= and save the file through a temporary object URL. */
export async function downloadArenaExport(sessionId: string, format: "markdown" | "json"): Promise<string> {
  const res = await fetch(`/api/arena/${encodeURIComponent(sessionId)}/export?format=${format}`, { method: "POST", credentials: "same-origin" });
  if (!res.ok) {
    let err: { error?: { code?: string; message?: string } } = {};
    try {
      err = await res.json();
    } catch {
      /* ignore */
    }
    throw new ClientApiError(res.status, err.error?.code ?? "HTTP_ERROR", err.error?.message ?? `Export failed (${res.status})`);
  }
  const blob = await res.blob();
  const cd = res.headers.get("Content-Disposition") ?? "";
  const filename = res.headers.get("X-Filename") ?? /filename="([^"]+)"/.exec(cd)?.[1] ?? `arena.${format === "json" ? "json" : "md"}`;
  const url = URL.createObjectURL(blob);
  const a = document.createElement("a");
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  a.remove();
  setTimeout(() => URL.revokeObjectURL(url), 2000);
  return filename;
}