const Busboy = require('busboy');
const fs = require('fs');
const checkTargetDir = require('./mkdir');
const path = require('path')


/**
 * 获取上传文件的后缀名
 * @param  {string} fileName 上传的文件的文件名
 * @return {string}      文件后缀名
 */
function getSuffixName(filename) {
  let nameList = filename.split('.');
  return nameList[nameList.length - 1];
}


/**
 * 获取唯一的文件名
 * @return {string}      文件名
 */
function getOnlyName() {
  return Math.random().toString(16).substr(2);
}



/**
* 上传文件，并生成唯一的文件名，根据上传时的文件名保持文件的后缀名
* @param  {object} ctx koa2上下文
* @return {promise}      
*/
async function uploadFile(ctx, target = './upload') {
  let formData, busboy,
    req = ctx.req;

  try {
    await checkTargetDir(target);
  } catch (e) {

  }

  busboy = new Busboy({headers: ctx.headers});
  formData = await new Promise((resolve, reject) => {
    let result = {};

    busboy.on('field', (filedname, val) => result[filedname] = val);
    busboy.on('file', async (filedname, file, filename) => {
      let locals = []
      result.name && locals.push('/' + result.name)
      result.dir && locals.push('/' + result.dir)

      let local = path.join.apply(path, locals)

      let l_path = filename;
      if (result.random) {
        l_path = `${getOnlyName()}.${getSuffixName(filename)}`;
      }
      
      let fileDir = path.join(target, local)

      try {
        await checkTargetDir(fileDir)
      } catch (e) {

      }

      fileDir = path.join(fileDir, l_path)
      file.pipe(fs.createWriteStream(fileDir));

      file.on('end', () => {
        result[filedname] = path.join(local, l_path);
      });
    });
    busboy.on('finish', () => resolve(result));
    busboy.on('error', err => reject(err));

    req.pipe(busboy);
  });
    
  return formData;
  }

module.exports = exports = uploadFile;