type JsonErrorPayload = {
  error?: string;
  message?: string;
  detail?: string;
};

const MAX_ERROR_TEXT = 240;

function summarizeResponseText(raw: string): string {
  const compact = raw.replace(/\s+/g, " ").trim();
  if (!compact) return "";
  if (compact.length <= MAX_ERROR_TEXT) return compact;
  return `${compact.slice(0, MAX_ERROR_TEXT - 3)}...`;
}

function defaultHttpMessage(response: Response): string {
  const suffix = response.statusText?.trim() ? ` ${response.statusText.trim()}` : "";
  return `HTTP ${response.status}${suffix}`;
}

function extractErrorMessage(
  response: Response,
  raw: string,
  payload: JsonErrorPayload | null,
): string {
  const candidate =
    (typeof payload?.error === "string" && payload.error.trim()) ||
    (typeof payload?.message === "string" && payload.message.trim()) ||
    (typeof payload?.detail === "string" && payload.detail.trim()) ||
    summarizeResponseText(raw);
  return candidate || defaultHttpMessage(response);
}

export async function fetchJsonResponse<T>(url: string, init?: RequestInit): Promise<T> {
  const response = await fetch(url, { cache: "no-store", ...init });
  const raw = await response.text();
  const trimmed = raw.trim();
  let payload: (T & JsonErrorPayload) | null = null;

  if (trimmed) {
    try {
      payload = JSON.parse(trimmed) as T & JsonErrorPayload;
    } catch {
      if (!response.ok) {
        throw new Error(extractErrorMessage(response, trimmed, null));
      }
      throw new Error(`Invalid JSON response from ${url}`);
    }
  }

  if (!response.ok) {
    throw new Error(extractErrorMessage(response, trimmed, payload));
  }

  if (payload !== null) {
    return payload as T;
  }

  return {} as T;
}

export async function readErrorMessage(response: Response): Promise<string> {
  const raw = (await response.text()).trim();
  let payload: JsonErrorPayload | null = null;
  if (raw) {
    try {
      payload = JSON.parse(raw) as JsonErrorPayload;
    } catch {
      payload = null;
    }
  }
  return extractErrorMessage(response, raw, payload);
}