const { imageSize } = require('image-size');
const cheerio = require('cheerio');
const superagent = require('superagent');
const htmlDocx = require('html-docx-js');

/**
 * 将Blob对象转换为Buffer
 * @param {Blob} blob - 要转换的Blob对象\
 * @returns {Buffer} - 转换后的Buffer对象
 * @throws {Error} - 如果转换失败，将抛出错误
 */
async function blobToBuffer(blob) {
   // 将Blob转换成ArrayBuffer
   const arrayBuffer = await blob.arrayBuffer();
   // 使用Node.js的Buffer.from方法从ArrayBuffer创建Buffer
   const buffer = Buffer.from(arrayBuffer);
   return buffer;
}

/**
 * 下载html里的网络图片并转换成base64格式
 * @param {String} htmlContent 
 * @return {String} - 处理后的HTML内容
 * @throws {Error} - 如果下载图片失败，将抛出错误
 */
async function preprocessHTMLContentWithBase64Images(htmlContent) {
   if (!htmlContent) {
      return '';
   }

   const $ = cheerio.load(htmlContent);
   const imgPromises = [];

   $('img').each(function (index, element) {
      const imgTag = $(element);
      let src = imgTag.attr('src');

      if (src && (src.startsWith('http://') || src.startsWith('https://'))) {
         const promise = superagent.get(src)
            .responseType('arraybuffer')
            .then(response => {
               const imageBuffer = Buffer.from(response.body, 'binary');
               const base64Image = imageBuffer.toString('base64');
               const dimensions = imageSize(imageBuffer);

               let mimeType = 'image/png'; // 默认值
               const contentTypeHeader = response.headers['content-type'];
               if (contentTypeHeader) {
                  mimeType = contentTypeHeader.split(';')[0];
               }

               imgTag.attr('src', `data:${mimeType};base64,${base64Image}`);

               // 如果图片宽度大于620px，则调整宽度为620px，并按比例缩放高度
               if (dimensions.width > 620) {
                  const ratio = dimensions.width / dimensions.height;
                  imgTag.attr('width', '620');
                  imgTag.attr('height', Math.round(620 / ratio));
               }
            })
            .catch(error => {
               console.error(`Error fetching image ${src} with superagent:`, error.message);
            });
         imgPromises.push(promise);
      }
   });

   await Promise.all(imgPromises);
   return $.html();
}

/**
 * 转换html内容为docx格式
 * @param {String} htmlContent
 * @return {Buffer} - 转换后的docx格式Buffer
 * @throws {Error} - 如果转换失败，将抛出错误
 */
async function convertHTMLToDOCX(htmlContent) {
   const processedHtml = await preprocessHTMLContentWithBase64Images(htmlContent);
   const docxBlob = htmlDocx.asBlob(processedHtml);
   const docxBuffer = blobToBuffer(docxBlob);
   return docxBuffer;
}

module.exports = {
   blobToBuffer,
   preprocessHTMLContentWithBase64Images,
   convertHTMLToDOCX,
}