/** 帖子附件客户端校验（与后端 setting / fileallow 对齐；安全边界仍在 Go） */

export const FILE_MAX_MB_DEFAULT = 20;
export const FILE_MAX_COUNT_DEFAULT = 10;

export function normalizeExt(nameOrExt: string): string {
  const base = nameOrExt.includes("/")
    ? nameOrExt.split(/[/\\]/).pop() || ""
    : nameOrExt;
  const i = base.lastIndexOf(".");
  const ext = (i >= 0 ? base.slice(i + 1) : base).trim().toLowerCase();
  return ext.replace(/[^a-z0-9]/g, "").slice(0, 16);
}

export function buildAcceptAttr(exts: string[], limit: boolean): string | undefined {
  if (!limit) return undefined;
  if (!exts.length) return undefined;
  return exts.map((e) => `.${e}`).join(",");
}

export function isAllowedPostFileName(
  name: string,
  opts: { limit: boolean; exts: string[] }
): boolean {
  if (!opts.limit) return true;
  const ext = normalizeExt(name);
  if (!ext) return false;
  return opts.exts.includes(ext);
}

export function formatMB(n: number): string {
  return `${n}MB`;
}

export type PostFileRejectReason = "size" | "type" | "count" | null;

export function rejectPostFile(
  file: File,
  opts: {
    limit: boolean;
    exts: string[];
    maxMB: number;
    maxCount: number;
    currentCount: number;
  }
): { reason: PostFileRejectReason; message?: string } {
  if (opts.currentCount >= opts.maxCount) {
    return { reason: "count", message: `最多 ${opts.maxCount} 个附件` };
  }
  const maxBytes = opts.maxMB * 1024 * 1024;
  if (file.size > maxBytes) {
    return { reason: "size", message: `附件不能超过 ${opts.maxMB}MB` };
  }
  if (!isAllowedPostFileName(file.name, opts)) {
    return { reason: "type", message: "不支持该附件格式" };
  }
  return { reason: null };
}