适用于uni app，微信小程序，网页端

function pathToBase64(path) {
    return new Promise(function(resolve, reject) {
        if (typeof window === 'object' && 'document' in window) {
            var canvas = document.createElement('canvas')
            var c2x = canvas.getContext('2d')
            var img = new Image
            img.onload = function() {
                canvas.width = img.width
                canvas.height = img.height
                c2x.drawImage(img, 0, 0)
                resolve(canvas.toDataURL())
            }
            img.onerror = reject
            img.src = path
            return
        }
        if (typeof plus === 'object') {
            var bitmap = new plus.nativeObj.Bitmap('bitmap' + Date.now())
            bitmap.load(path, function() {
                try {
                    var base64 = bitmap.toBase64Data()
                } catch (error) {
                    reject(error)
                }
                bitmap.clear()
                resolve(base64)
            }, function(error) {
                bitmap.clear()
                reject(error)
            })
            return
        }
        if (typeof wx === 'object' && wx.canIUse('getFileSystemManager')) {
            wx.getFileSystemManager().readFile({
                filePath: path,
                encoding: 'base64',
                success: function(res) {
                    resolve('data:image/png;base64,' + res.data)
                },
                fail: function(error) {
                    reject(error)
                }
            })
            return
        }
        reject(new Error('not support'))
    })
}

function base64ToPath(base64) {
    return new Promise(function(resolve, reject) {
        if (typeof window === 'object' && 'document' in window) {
            base64 = base64.split(',')
            var type = base64[0].match(/:(.*?);/)[1]
            var str = atob(base64[1])
            var n = str.length
            var array = new Uint8Array(n)
            while (n--) {
                array[n] = str.charCodeAt(n)
            }
            return resolve((window.URL || window.webkitURL).createObjectURL(new Blob([array], { type: type })))
        }
        var extName = base64.match(/data\:\S+\/(\S+);/)
        if (extName) {
            extName = extName[1]
        } else {
            reject(new Error('base64 error'))
        }
        var fileName = Date.now() + '.' + extName
        if (typeof plus === 'object') {
            var bitmap = new plus.nativeObj.Bitmap('bitmap' + Date.now())
            bitmap.loadBase64Data(base64, function() {
                var filePath = '_doc/uniapp_temp/' + fileName
                bitmap.save(filePath, {}, function() {
                    bitmap.clear()
                    resolve(filePath)
                }, function(error) {
                    bitmap.clear()
                    reject(error)
                })
            }, function(error) {
                bitmap.clear()
                reject(error)
            })
            return
        }
        if (typeof wx === 'object' && wx.canIUse('getFileSystemManager')) {
            var filePath = wx.env.USER_DATA_PATH + '/' + fileName
            wx.getFileSystemManager().writeFile({
                filePath: filePath,
                data: base64.replace(/^data:\S+\/\S+;base64,/, ''),
                encoding: 'base64',
                success: function() {
                    resolve(filePath)
                },
                fail: function(error) {
                    reject(error)
                }
            })
            return
        }
        reject(new Error('not support'))
    })
}

function dataURLtoFile(dataurl, filename) { 
    if(!filename){
        filename = new Date().getTime()
    }
    var arr = dataurl.split(','),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    
    return new File([u8arr], filename + '.' + mime.split('/')[1], { type: mime });
}


export {pathToBase64,base64ToPath,dataURLtoFile}