PdfDownloader.kt

PdfDownloader.kt

class PdfDownloader @Inject constructor(
  private val context: Context,
  private val yourApi: YourApi
) {

  private class DownloadException(message: String, cause: Throwable? = null) : RuntimeException(message, cause)
  
  suspend fun download(url: String, fileName: String): String = withContext(Dispatchers.IO) {
    val file = createFile(fileName)

    val response = yourApi.downloadPdf(url)
    // this would look like this in YourApi:
    // @Streaming @GET
    // suspend fun downloadPdf(@Url url: String): Response<ResponseBody>

    val inputStream = response.body()?.byteStream() ?: throw DownloadException("Download body is null")
    inputStream.use { input ->
      FileOutputStream(file).use { output -> input.copyTo(output) }
    }
    file.absolutePath
  }
  
  private fun createFile(fileName: String) = try {
      val directory = context.getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS)
      File.createTempFile("download_", fileName, directory)
    } catch (e: IOException) {
      throw DownloadException("Error while creating download file", e)
    }
  }

  private fun InputStream.copyTo(output: FileOutputStream) {
    val buffer = ByteArray(4 * 1024)
    while (true) {
      val byteCount = read(buffer)
      if (byteCount < 0) break
      output.write(buffer, 0, byteCount)
    }
    output.flush()
  }
}