/**
 * 命名工具（A0-SH-01）：文件名清洗 + 同名自动加序号（PRD R-01）
 * 浏览器 / Node 通用，不依赖 node:path。
 */

const ILLEGAL_FILENAME_CHARS = /[\\/:*?"<>|]/g;
const RESERVED_FILENAMES = new Set([
  'CON',
  'PRN',
  'AUX',
  'NUL',
  'COM1',
  'COM2',
  'COM3',
  'COM4',
  'COM5',
  'COM6',
  'COM7',
  'COM8',
  'COM9',
  'LPT1',
  'LPT2',
  'LPT3',
  'LPT4',
  'LPT5',
  'LPT6',
  'LPT7',
  'LPT8',
  'LPT9',
]);

const MAX_FILENAME_LENGTH = 120;

export interface SanitizeFilenameOptions {
  maxLength?: number;
  replacement?: string;
  fallback?: string;
}

/** 去掉控制字符（\u0000-\u001f、\u007f），保留常规空白 */
function stripControlChars(input: string): string {
  let output = '';
  for (const char of input) {
    const code = char.codePointAt(0) ?? 0;
    if (code >= 0x20 && code !== 0x7f) {
      output += char;
    }
  }
  return output;
}

/** 清洗文件名：去除非法字符 / 控制字符 / 首尾空格与点，中文原样保留 */
export function sanitizeFilename(input: string, options: SanitizeFilenameOptions = {}): string {
  const maxLength = options.maxLength ?? MAX_FILENAME_LENGTH;
  const replacement = options.replacement ?? '_';
  const fallback = options.fallback ?? '未命名';

  let name = stripControlChars(input.normalize('NFC'))
    .replace(ILLEGAL_FILENAME_CHARS, replacement)
    .trim();
  name = name.replace(/^[.\s]+|[.\s]+$/g, '');

  if (name.length === 0 || name.replaceAll(replacement, '').trim().length === 0) {
    return fallback;
  }
  if (RESERVED_FILENAMES.has(name.toUpperCase())) {
    name = `${name}_`;
  }
  if (name.length > maxLength) {
    const dotIndex = name.lastIndexOf('.');
    const extension = dotIndex > 0 ? name.slice(dotIndex) : '';
    const base = dotIndex > 0 ? name.slice(0, dotIndex) : name;
    const keep = Math.max(1, maxLength - extension.length);
    name = `${base.slice(0, keep)}${extension}`;
  }
  return name;
}

const SEQUENCE_PATTERN = /^(.*)-(\d{2,})$/;

function splitExtension(name: string): { stem: string; extension: string } {
  const dotIndex = name.lastIndexOf('.');
  if (dotIndex <= 0 || dotIndex === name.length - 1) {
    return { stem: name, extension: '' };
  }
  return { stem: name.slice(0, dotIndex), extension: name.slice(dotIndex) };
}

/**
 * 同名自动加序号（R-01）：从 base-02 开始尝试到 maxAttempts，全部占用则抛错。
 * 已带序号的名字会基于其原始基名继续递增；扩展名保持不变。
 */
export function dedupeName(name: string, existing: ReadonlySet<string>, maxAttempts = 999): string {
  if (!existing.has(name)) {
    return name;
  }
  const { stem, extension } = splitExtension(name);
  const matched = SEQUENCE_PATTERN.exec(stem);
  const root = matched?.[1] ?? stem;
  for (let sequence = 2; sequence <= maxAttempts; sequence += 1) {
    const candidate = `${root}-${String(sequence).padStart(2, '0')}${extension}`;
    if (!existing.has(candidate)) {
      return candidate;
    }
  }
  throw new RangeError(`同名文件过多，无法为「${name}」生成序号`);
}