'use strict';

/**
 * 通用表格导出
 * --------------------------------------------------------------------------
 * 把 [{ name, header: string[], rows: any[][] }] 渲染成：
 *   - xlsx：多工作表工作簿（基于 backend 已依赖的 xlsx 包）
 *   - csv ：单工作表、带 UTF-8 BOM（Excel 直接打开中文不乱码）
 * 语义与 frontend/src/utils/tableExport.js 的「表头 + 行」保持一致。
 */

const xlsx = require('xlsx');

const XLSX_CONTENT_TYPE = 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet';
const CSV_CONTENT_TYPE = 'text/csv; charset=utf-8';

// Excel 工作表名限制：<=31 字符，且不能包含 : \ / ? * [ ]
const sanitizeSheetName = (name, fallback) => {
  const cleaned = String(name || '').replace(/[:\\/?*[\]]/g, ' ').replace(/\s+/g, ' ').trim();
  return (cleaned || fallback).slice(0, 31);
};

const toCellValue = (value) => (
  value === null || value === undefined || value === '' ? '' : value
);

const sheetToAoa = (sheet) => ([
  (sheet?.header || []).map(toCellValue),
  ...((sheet?.rows || []).map((row) => (row || []).map(toCellValue))),
]);

/** 多工作表 xlsx buffer；工作表名重复/非法时自动去重与截断 */
const buildXlsxBuffer = (sheets = []) => {
  const workbook = xlsx.utils.book_new();
  const usedNames = new Set();

  sheets.forEach((sheet, index) => {
    const base = sanitizeSheetName(sheet?.name, `工作表${index + 1}`);
    let name = base;
    let suffix = 2;
    while (usedNames.has(name)) {
      name = `${base.slice(0, 27)}(${suffix})`;
      suffix += 1;
    }
    usedNames.add(name);

    const worksheet = xlsx.utils.aoa_to_sheet(sheetToAoa(sheet));
    worksheet['!cols'] = (sheet?.header || []).map((title) => ({
      wch: Math.max(10, Math.min(32, String(title || '').length * 2 + 6)),
    }));
    xlsx.utils.book_append_sheet(workbook, worksheet, name);
  });

  return xlsx.write(workbook, { type: 'buffer', bookType: 'xlsx' });
};

const quoteCsvCell = (value) => {
  const text = value === null || value === undefined ? '' : String(value);
  return /[",\r\n]/.test(text) ? `"${text.replace(/"/g, '""')}"` : text;
};

/** 单工作表 csv buffer（只取第一个工作表），前置 BOM */
const buildCsvBuffer = (sheets = []) => {
  const sheet = sheets[0] || { header: [], rows: [] };
  const lines = [(sheet.header || []).map(quoteCsvCell).join(',')];
  (sheet.rows || []).forEach((row) => {
    lines.push((row || []).map(quoteCsvCell).join(','));
  });
  return Buffer.from(`\ufeff${lines.join('\r\n')}`, 'utf8');
};

const sanitizeFileName = (fileName) => String(fileName || '导出数据').replace(/[\\/:*?"<>|]/g, '_').trim() || '导出数据';

/**
 * 直接把导出结果写回响应。
 * @param {import('express').Response} res
 * @param {{ fileName?: string, format?: 'xlsx'|'csv', sheets?: Array }} payload
 */
const sendWorkbookDownload = (res, { fileName, format = 'xlsx', sheets = [] } = {}) => {
  const isCsv = String(format).toLowerCase() === 'csv';
  const exportSheets = isCsv ? sheets.slice(0, 1) : sheets;
  const buffer = isCsv ? buildCsvBuffer(exportSheets) : buildXlsxBuffer(exportSheets);
  const totalRows = exportSheets.reduce((sum, sheet) => sum + ((sheet?.rows || []).length), 0);
  const fullName = `${sanitizeFileName(fileName)}${isCsv ? '.csv' : '.xlsx'}`;

  res.setHeader('Content-Type', isCsv ? CSV_CONTENT_TYPE : XLSX_CONTENT_TYPE);
  res.setHeader('Content-Disposition', `attachment; filename*=UTF-8''${encodeURIComponent(fullName)}`);
  res.setHeader('X-Export-Count', String(totalRows));
  res.send(buffer);
  return { totalRows, fullName };
};

module.exports = {
  XLSX_CONTENT_TYPE,
  CSV_CONTENT_TYPE,
  sanitizeSheetName,
  buildXlsxBuffer,
  buildCsvBuffer,
  sendWorkbookDownload,
};