export type ExportColumnDef<T> = {
  key: string;
  header: string;
  value: (row: T) => string | number;
};

/** 按请求的列 key 过滤导出列；未传则导出全部 */
export function pickExportColumns<T>(
  defs: ExportColumnDef<T>[],
  requestedKeys?: string[],
): ExportColumnDef<T>[] {
  if (!requestedKeys?.length) return defs;
  const byKey = new Map(defs.map((d) => [d.key, d]));
  return requestedKeys.map((k) => byKey.get(k)).filter((d): d is ExportColumnDef<T> => !!d);
}

export function parseExportColumnKeys(raw?: string): string[] | undefined {
  if (!raw?.trim()) return undefined;
  const keys = raw
    .split(',')
    .map((k) => k.trim())
    .filter(Boolean);
  return keys.length ? keys : undefined;
}

export function buildCsvFromColumns<T>(
  defs: ExportColumnDef<T>[],
  rows: T[],
  requestedKeys?: string[],
): { csv: string; count: number } {
  const active = pickExportColumns(defs, requestedKeys);
  if (!active.length) {
    return { csv: '\uFEFF', count: 0 };
  }
  const header = active.map((d) => d.header).join(',');
  const body = rows.map((row) =>
    active
      .map((d) => {
        const v = d.value(row);
        const s = v == null ? '' : String(v);
        return s.includes(',') || s.includes('"') || s.includes('\n')
          ? `"${s.replace(/"/g, '""')}"`
          : s;
      })
      .join(','),
  );
  return { csv: `\uFEFF${[header, ...body].join('\n')}`, count: rows.length };
}