package org.thoughtcrime.securesms.crypto;


import android.support.annotation.NonNull;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.Mac;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/**
 * Constructs an OutputStream that encrypts data written to it with the AttachmentSecret provided.
 *
 * The on-disk format is very simple, and intentionally no longer includes authentication.
 */
public class ModernEncryptingPartOutputStream {

  public static OutputStream createFor(@NonNull AttachmentSecret attachmentSecret, byte[] random, File file)
      throws IOException
  {
    try {
      Mac mac = Mac.getInstance("HmacSHA256");
      mac.init(new SecretKeySpec(attachmentSecret.getModernKey(), "HmacSHA256"));

      FileOutputStream fileOutputStream = new FileOutputStream(file);
      byte[]           iv               = new byte[16];
      byte[]           key              = mac.doFinal(random);

      Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
      cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(iv));

      return new CipherOutputStream(fileOutputStream, cipher);
    } catch (NoSuchAlgorithmException | InvalidKeyException | InvalidAlgorithmParameterException | NoSuchPaddingException e) {
      throw new AssertionError(e);
    }
  }

}