Whiteboard integration

interface RTCClientEvent {
    /**
     * You joined the channel successfully
     * @param whiteBoard Whiteboard URL, normally not empty; null means the line configuration is abnormal
     */
    fun onJoinSucceed(channel: String, uid: String, whiteBoard: String?)
    // ...
}

override fun onJoinSucceed(channel: String, uid: String, whiteBoard: String?) {
    if (!whiteBoard.isNullOrEmpty()) {
        // whiteBoard is the whiteboard URL; hand it to the WebView to load
        openWhiteBoard(whiteBoard)
    }
}

val setting = webView.settings
setting.javaScriptEnabled = true                       // Required: the whiteboard depends on JS
setting.domStorageEnabled = true                       // Required: the whiteboard depends on DOM Storage
setting.databaseEnabled = true
setting.javaScriptCanOpenWindowsAutomatically = true

val param = "&no_menu=1&export_btn=1"
webView.loadUrl(whiteBoard + param)

webView.addJavascriptInterface(JsBridgeForWhiteboard(callback), "AndroidInterface")

class JsBridgeForWhiteboard(private val callback: Callback) {

    @JavascriptInterface
    fun onExportImage(dataUrl: String) {   // Whiteboard exported an image
        callback.onExportImage(dataUrl)
    }

    @JavascriptInterface
    fun onWbDestroy(reason: String) {      // Whiteboard destroyed notification
        callback.onWbDestroy(reason)
    }

    interface Callback {
        fun onExportImage(dataUrl: String)
        fun onWbDestroy(reason: String)
    }
}

override fun onDestroy() {
    super.onDestroy()
    webView.destroy()
}

private fun saveBase64DataUrl(dataUrl: String) {
    val prefix = "base64,"
    val index = dataUrl.indexOf(prefix)
    if (index == -1) return
    val bytes = Base64.decode(dataUrl.substring(index + prefix.length), Base64.DEFAULT)
    // Write bytes to the gallery / a file (on Android 9 and earlier, request the WRITE permission first)
}

webView.webChromeClient = object : WebChromeClient() {
    override fun onPermissionRequest(request: PermissionRequest) {
        request.grant(request.resources)
    }

    override fun onShowFileChooser(
        webView: WebView?,
        filePathCallback: ValueCallback<Array<Uri>>?,
        params: FileChooserParams?
    ): Boolean {
        // Take a photo / pick from the gallery; once you have the uri:
        // filePathCallback?.onReceiveValue(arrayOf(uri))
        // User canceled: filePathCallback?.onReceiveValue(null)
        return true
    }
}

webView.webViewClient = object : WebViewClient() {
    override fun onPageFinished(view: WebView?, url: String?) {
        super.onPageFinished(view, url)
        // The methods are attached only after the page finishes loading; calling them earlier gives undefined
        webView.evaluateJavascript("window.setReadonly(${!canDraw})", null)
    }
}

// You can call it again at any time during the call without reloading the page
fun revokeDrawPermission() {
    webView.evaluateJavascript("window.setReadonly(true)", null)
}