const TRAILING_SLASH = /\/$/;

export function getBackendBaseUrl(): string {
  const raw = process.env.BACKEND_URL ?? process.env.NEXT_PUBLIC_BACKEND_URL;
  if (!raw) {
    throw new Error("BACKEND_URL 未配置");
  }
  return raw.replace(TRAILING_SLASH, "");
}

export function tryGetBackendBaseUrl(): string | null {
  try {
    return getBackendBaseUrl();
  } catch {
    return null;
  }
}

type SearchParamsInit = Record<string, string | number | boolean | undefined> | URLSearchParams;

export function buildBackendUrl(path: string, params?: SearchParamsInit): URL {
  const base = getBackendBaseUrl();
  const url = new URL(path, base);
  if (params) {
    const search =
      params instanceof URLSearchParams
        ? params
        : new URLSearchParams(
            Object.entries(params).reduce<Record<string, string>>((acc, [key, value]) => {
              if (value !== undefined) {
                acc[key] = String(value);
              }
              return acc;
            }, {}),
          );
    search.forEach((value, key) => {
      if (value !== undefined && value !== null) {
        url.searchParams.set(key, value);
      }
    });
  }
  return url;
}

export async function fetchBackend(path: string, init?: RequestInit, params?: SearchParamsInit) {
  const url = buildBackendUrl(path, params);
  return fetch(url, init);
}