import * as XLSX from 'xlsx'
function openDownloadDialog(url, saveName) {
    if (typeof url == 'object' && url instanceof Blob) {
        url = URL.createObjectURL(url); // 创建blob地址
    }
    let aLink = document.createElement('a');
    aLink.href = url;
    aLink.download = saveName || ''; // HTML5新增的属性，指定保存文件名，可以不要后缀，注意，file:///模式下不会生效
    let event;
    if (window.MouseEvent) event = new MouseEvent('click');
    else {
        event = document.createEvent('MouseEvents');
        event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
    }
    aLink.dispatchEvent(event);
}

// 将一个sheet转成最终的excel文件的blob对象，然后利用URL.createObjectURL下载
function sheet2blob(sheet, sheetName) {
    sheetName = sheetName || 'sheet1';
    let workbook = {
        SheetNames: [sheetName],
        Sheets: {}
    };
    workbook.Sheets[sheetName] = sheet;
    // 生成excel的配置项
    let wopts = {
        bookType: 'xlsx', // 要生成的文件类型
        bookSST: false, // 是否生成Shared String Table，官方解释是，如果开启生成速度会下降，但在低版本IOS设备上有更好的兼容性
        type: 'binary'
    };
    let wbout = XLSX.write(workbook, wopts);
    let blob = new Blob([s2ab(wbout)], {type: "application/octet-stream"});
    // 字符串转ArrayBuffer
    function s2ab(s) {
        let buf = new ArrayBuffer(s.length);
        let view = new Uint8Array(buf);
        for (let i = 0; i != s.length; ++i) view[i] = s.charCodeAt(i) & 0xFF;
        return buf;
    }
    return blob;
}
 /**
  * @description: 导出excel
  * @param {*} arr 数据是数组包含的对象
  * @param {*} name 名字
  * @return {*}
  */
 function exp(arr,name="导出") {
    var sheet = XLSX.utils.json_to_sheet(arr);
    // excel宽高设置
    sheet["!cols"]= arr.map(item=>{
        return {wch:30}
    })
    openDownloadDialog(sheet2blob(sheet), name+'.xlsx')
}
export default exp;