export class ApiError extends Error {
  constructor(
    message: string,
    readonly status: number,
  ) {
    super(message);
  }
}

let sessionReady: Promise<void> | null = null;

async function ensureSession(): Promise<void> {
  if (!sessionReady) {
    sessionReady = fetch("/api/session", { cache: "no-store" }).then((response) => {
      if (!response.ok) throw new Error("Could not initialize the private MatchDay session");
    });
  }
  try {
    await sessionReady;
  } catch (error) {
    sessionReady = null;
    throw error;
  }
}

function readableDetail(detail: unknown, fallback: string): string {
  if (typeof detail === "string" && detail.trim()) return detail;
  if (Array.isArray(detail)) {
    const messages = detail
      .map((item) => {
        if (!item || typeof item !== "object") return String(item || "");
        const record = item as { msg?: unknown; loc?: unknown };
        const message = typeof record.msg === "string" ? record.msg : "Invalid value";
        const location = Array.isArray(record.loc)
          ? record.loc.filter((part) => part !== "body").join(".")
          : "";
        return location ? `${location}: ${message}` : message;
      })
      .filter(Boolean);
    if (messages.length) return messages.join("; ");
  }
  if (detail && typeof detail === "object" && "msg" in detail) {
    const message = (detail as { msg?: unknown }).msg;
    if (typeof message === "string") return message;
  }
  return fallback;
}

export async function api<T>(path: string, init?: RequestInit): Promise<T> {
  await ensureSession();
  const response = await fetch(`/api/backend${path}`, {
    ...init,
    headers: {
      "content-type": "application/json",
      ...(init?.headers || {}),
    },
    cache: "no-store",
  });
  if (!response.ok) {
    const payload = await response.json().catch(() => ({}));
    throw new ApiError(
      readableDetail(payload.detail, `Request failed (${response.status})`),
      response.status,
    );
  }
  if (response.status === 204) return undefined as T;
  return response.json() as Promise<T>;
}