const watermark = ({
    // 使用 ES6 的函式預設值方式設定引數的預設取值
    // 具體參見 https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Functions/Default_parameters
    container = document.body,
    width = '400px',
    height = '400px', 
    textAlign = 'left',
    textBaseline = 'bottom',
    font = '14px Microsoft Yahei
 
',
    fillStyle = 'rgba(184, 184, 184, 0.4)',
    content = '',
    rotate = '24',
    zIndex = 1000
  } = {}, ...res) => {
const args = res
const canvas = document.createElement('canvas')

canvas.setAttribute('width', width)
canvas.setAttribute('height', height)
const ctx = canvas.getContext('2d')

ctx.textAlign 
 
= textAlign
ctx.textBaseline = textBaseline
ctx.font = font
ctx.fillStyle = fillStyle
ctx.rotate(Math.PI / 180 * rotate)
ctx.fillText(content, 100, parseFloat(height) / 2) 
// ctx.fillText(content, 20, parseFloat(height) / 2) 

const base64Url = canvas.toDataURL()
const __wm = document.querySelector('.__wm')
 
const watermarkDiv = __wm || document.createElement('div')
const styleStr = `
position:absolute;
top:0;
left:0;
width:100%;
height:100%;
z-index:${zIndex};
pointer-events:none;
background-repeat:repeat;
background-image:url('${base64Url}')`

watermarkDiv.setAttribute('style', styleStr)
watermarkDiv.classList.add('__wm')

if (!__wm) {
container.style.position = 'relative'
container.insertBefore(watermarkDiv, container.firstChild)
}

const MutationObserver = window.MutationObserver || window.WebKitMutationObserver
if (MutationObserver) {
let mo = new MutationObserver(function () {
const __wm = document.querySelector('.__wm')
console.log(__wm)
// 只在__wm元素變動才重新呼叫 __canvasWM
if ((__wm && __wm.getAttribute('style') !== styleStr) || !__wm) {
// 避免一直觸發
mo.disconnect()
mo = null
watermark(JSON.parse(JSON.stringify(args)))
}
})

mo.observe(container, {
attributes: true,
subtree: true,
childList: true
})
}

}

export default watermark