import jsPDF from 'jspdf'
import html2canvas from 'html2canvas'

/*
* 使用说明
* ele:需要导出pdf的容器元素(dom节点 不是id)
* pdfFileName: 导出文件的名字 通过调用outPutPdfFn方法也可传参数改变
* splitClassName: 避免分段截断的类名 当pdf有多页时需要传入此参数 , 避免pdf分页时截断元素  如表格<tr class="itemClass"></tr>
* 调用方式 先 let pdf = new PdfLoader(ele, 'pdf' ,'itemClass');
* 若想改变pdf名称 pdf.outPutPdfFn(fileName);  outPutPdfFn方法返回一个promise 可以使用then方法处理pdf生成后的逻辑
* */
class PdfLoader {
  constructor(ele, pdfFileName, splitClassName) {
    this.ele = ele
    this.pdfFileName = pdfFileName
    this.splitClassName = splitClassName
    this.A4_WIDTH = 595
    this.A4_HEIGHT = 842
  }

  async getPDF(resolve) {
    const ele = this.ele;
    let eleme = this.ele;
    eleme.style.width="800px";
    const pdfFileName = this.pdfFileName
    const eleW = ele.offsetWidth// 获得该容器的宽
    const eleH = ele.scrollHeight;// 获得该容器的高
    const eleOffsetTop = ele.offsetTop// 获得该容器到文档顶部的距离
    const eleOffsetLeft = ele.offsetLeft// 获得该容器到文档最左的距离
    const canvas = document.createElement('canvas')
    canvas.width = eleW * 3// 将画布宽&&高放大两倍
    canvas.height = eleH * 3
    const context = canvas.getContext('2d')
    context.scale(3,3) // 增强图片清晰度
    context.translate(-eleOffsetLeft , -eleOffsetTop)
    html2canvas(eleme, {
      useCORS: true// 允许canvas画布内可以跨域请求外部链接图片, 允许跨域请求。
    }).then(async canvas => {
      const contentWidth = canvas.width
      const contentHeight = canvas.height
      // 一页pdf显示html页面生成的canvas高度;
      const pageHeight = (contentWidth / this.A4_WIDTH) * this.A4_HEIGHT // 这样写的目的在于保持宽高比例一致 pageHeight/canvas.width = a4纸高度/a4纸宽度// 宽度和canvas.width保持一致
      // 未生成pdf的html页面高度
      let leftHeight = contentHeight
      // 页面偏移
      let position = 20
      // a4纸的尺寸[595,842],单位像素，html页面生成的canvas在pdf中图片的宽高
      const imgWidth = this.A4_WIDTH - 40 // -10为了页面有右边距
      const imgHeight = (this.A4_WIDTH / contentWidth) * contentHeight
      const pageData = canvas.toDataURL('image/jpeg', 1.0)
      const pdf = jsPDF('', 'pt', 'a4')
      // 有两个高度需要区分，一个是html页面的实际高度，和生成pdf的页面高度(841.89)
      // 当内容未超过pdf一页显示的范围，无需分页
      if (leftHeight < pageHeight) {
        // 在pdf.addImage(pageData, 'JPEG', 左，上，宽度，高度)设置在pdf中显示；
        pdf.addImage(pageData, 'JPEG', 20, 20, imgWidth, imgHeight)
      } else {
        // 分页
        while (leftHeight > 0) {
          pdf.addImage(pageData, 'JPEG', 20, position, imgWidth, imgHeight)
          leftHeight -= pageHeight
          position -= this.A4_HEIGHT
          // 避免添加空白页
          if (leftHeight > 0) {
            pdf.addPage()
          }
        }
      }
      pdf.save(pdfFileName + '.pdf', { returnPromise: true }).then(() => {
        // 去除添加的空div 防止页面混乱
        const doms = document.querySelectorAll('.emptyDiv')
        for (let i = 0; i < doms.length; i++) {
          doms[i].remove()
        }
      })
      this.ele.style.height = ''
      resolve()
    })
  }
	//此方法是防止（图表之类）内容因为A4纸张问题被截断
  async outPutPdfFn(pdfFileName) {
    return new Promise((resolve, reject) => {
      this.ele.style.height = 'initial'
      pdfFileName ? this.pdfFileName = pdfFileName : null
      const target = this.ele
      const pageHeight = target.scrollWidth / this.A4_WIDTH * this.A4_HEIGHT
      // 获取分割dom，此处为class类名为item的dom
      const domList = document.getElementsByClassName(this.splitClassName)
      // 进行分割操作，当dom内容已超出a4的高度，则将该dom前插入一个空dom，把他挤下去，分割
      let pageNum = 1 // pdf页数
      const eleBounding = this.ele.getBoundingClientRect()
      for (let i = 0; i < domList.length; i++) {
        const node = domList[i]
        const bound = node.getBoundingClientRect()
        const offset2Ele = bound.top - eleBounding.top
        const currentPage = Math.ceil((bound.bottom - eleBounding.top) / pageHeight) // 当前元素应该在哪一页
        if (pageNum < currentPage) {
          pageNum++
          const divParent = domList[i].parentNode // 获取该div的父节点
          const newNode = document.createElement('div')
          newNode.className = 'emptyDiv'
          newNode.style.background = 'white'
          newNode.style.height = (pageHeight * (pageNum - 1) - offset2Ele + 30) + 'px' // +30为了在换下一页时有顶部的边距
          newNode.style.width = '100%'
          divParent.insertBefore(newNode, node) //在每一个节点前面插入一个空的新节点，防止内容被分割截断
        }
      }
      // 异步函数，导出成功后处理交互
      this.getPDF(resolve, reject)
    })
  }
}
export default PdfLoader

