// utils/export.ts
export type ExportParams = {
  baseUrl?: string;               // e.g. process.env.NEXT_PUBLIC_API_URL
  site: string;                   // PROJ-0028
  suffix?: "grid" | "solar";      // default "grid"
  serial?: string | null;         // device id like "01"
  day?: string;                   // "YYYY-MM-DD" (preferred)
  start?: string;                 // ISO string (if not using day)
  end?: string;                   // ISO string (if not using day)
  columns?: string[];             // optional list of columns
  localTz?: string;               // default "Asia/Kuala_Lumpur"
};

export function buildExportUrl(p: ExportParams): string {
  const {
    baseUrl = "",
    site,
    suffix = "grid",
    serial,
    day,
    start,
    end,
    columns,
    localTz = "Asia/Kuala_Lumpur",
  } = p;

  const params = new URLSearchParams();
  params.set("site", site);
  params.set("suffix", suffix);
  params.set("local_tz", localTz);

  const s = serial?.trim();
  if (s) params.set("serial", s);

  if (day) {
    params.set("day", day); // simple whole-day export
  } else {
    if (!start || !end) throw new Error("Provide either day=YYYY-MM-DD or both start and end.");
    params.set("start", start); // URLSearchParams will encode '+' correctly
    params.set("end", end);
  }

  if (columns?.length) {
    // backend expects ?columns=... repeated; append each
    columns.forEach(c => params.append("columns", c));
  }

  // ensure there's a single slash join for /export/xlsx
  const root = baseUrl.replace(/\/+$/, "");
  return `${root}/export/xlsx?${params.toString()}`;
}

/** Parse filename from Content-Disposition (handles RFC5987 filename*) */
export function getFilenameFromCD(cd: string | null): string | null {
  if (!cd) return null;

  // filename*=UTF-8''encoded-name.xlsx
  const star = /filename\*\s*=\s*([^']*)''([^;]+)/i.exec(cd);
  if (star && star[2]) {
    try {
      return decodeURIComponent(star[2]);
    } catch {
      return star[2];
    }
  }

  // filename="name.xlsx" OR filename=name.xlsx
  const plain = /filename\s*=\s*("?)([^";]+)\1/i.exec(cd);
  return plain ? plain[2] : null;
}