FileDownloader.kt

import java.io.*

class FileDownloader(
        val onProgressUpdate: ((fileSize: Long, downloadedSize: Long) -> Unit)?,
        val onDownloadComplete: () -> Unit) {

    var bufferSize = 1024 * 8
    var singleReadSize = 1024 * 4
    var progressNotificationDelay = 1000

    fun startDownload(contentLength: Long, byteStream: InputStream, outputStream: OutputStream) {
        val data = ByteArray(singleReadSize)
        val bis = BufferedInputStream(byteStream, bufferSize)
        var total: Long = 0
        val startTime = System.currentTimeMillis()
        var timeCount = 1

        var count = bis.read(data)
        while (count != -1) {
            total += count.toLong()
            val currentTime = System.currentTimeMillis() - startTime
            if (currentTime > progressNotificationDelay * timeCount) {
                onProgressUpdate?.let { it(contentLength, total) }
                timeCount++
            }
            outputStream.write(data, 0, count)
            count = bis.read(data)
        }
        onDownloadComplete()

        outputStream.flush()
        outputStream.close()
        bis.close()
    }

}