Android or Xamarin - Relative path between Assets and Data Directory

Question

I have a folder inside my App Directory which contains an SDK in JavaScript for reading EPUBS. Inside a html file, there is one section of the code where the SDK tries to call the epubs unzipped folder like this:

<script language="JavaScript" type="text/javascript">

    "use strict";

    var Book = ePub("../reader/moby-dick/");

</script>

I need to get the EPUB's folder relative path for putting into this variable. My epub's folder is in the following path :

/data/data/<PackageName>/files/.config/moby-dick/ 

Seems that I only can call into the SDK directory. But I was able to perform this on iOS using relative paths.

Can anyone help me? Is there any solution to implement this? Thanks in advance.

EDIT : CODE

index.html

<script>

var Book;

document.addEventListener("deviceready",loadBook, false);

function loadBook(path) {
    window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, function(fileSystem) {
        fileSystem.root.getDirectory("/data/data/<PackageName>/files/.config/9788415028147", {create: false, exclusive:false}, function(fileEntry){
            console.log(fileEntry.toURL());
            Book = ePub(fileEntry.toURL());
            Book.renderTo(area);
        });
    });
}
</script>

xamarinclass.cs

var url = new Uri(Book.url);
var supportDir = System.Environment.GetFolderPath (System.Environment.SpecialFolder.ApplicationData);

string localFilename = System.IO.Path.GetFileName(url.AbsolutePath);
string localFilenameWithoutExt = System.IO.Path.GetFileNameWithoutExtension(url.AbsolutePath);
string localPath = System.IO.Path.Combine (supportDir, localFilename);
string localPathWithoutExt = System.IO.Path.Combine (supportDir, localFilenameWithoutExt);

if(!Directory.Exists(supportDir)) {
    Directory.CreateDirectory(supportDir);
}

if (!Directory.Exists (localPathWithoutExt)) {
    var webClient = new WebClient ();
    webClient.DownloadDataAsync (url);
    webClient.DownloadDataCompleted += (s, y) => {
        var bytes = y.Result;
        System.IO.File.WriteAllBytes (localPath, bytes);
        Directory.CreateDirectory (localPathWithoutExt);
        ZipFile.ExtractToDirectory (localPath, localPathWithoutExt);
        System.IO.File.Delete (localPath);
    }
}