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// Copyright 2016 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.archivepatcher.applier;

import com.google.archivepatcher.applier.bsdiff.BsDiffDeltaApplier;
import com.google.archivepatcher.shared.DeltaFriendlyFile;
import com.google.archivepatcher.shared.IDeflater;
import com.google.archivepatcher.shared.RandomAccessFileOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.function.BiFunction;
import java.util.zip.Deflater;

/**
 * Applies V1 patches.
 */
public class FileByFileV1DeltaApplier implements DeltaApplier {

  /**
   * Default size of the buffer to use for copying bytes in the recompression stream.
   */
  private static final int DEFAULT_COPY_BUFFER_SIZE = 32768;

  /**
   * The temp directory to use.
   */
  private final File tempDir;
  private final BiFunction deflaterFactory;

  /**
   * Creates a new delta applier that will use the default temp directory for working files. This is
   * equivalent to calling {@link #FileByFileV1DeltaApplier(File, BiFunction)}
   * with a null file argument.
   */
  public FileByFileV1DeltaApplier(BiFunction deflaterFactory) {
    this(null, deflaterFactory);
  }

  /**
   * Creates a new delta applier that will use the specified temp directory.
   *
   * @param tempDir a temp directory where the delta-friendly old blob can be written during the
   *     patch application process; if null, the system's default temporary directory is used
   */
  public FileByFileV1DeltaApplier(File tempDir, BiFunction deflaterFactory) {
    if (tempDir == null) {
      tempDir = new File(System.getProperty("java.io.tmpdir"));
    }
    this.tempDir = tempDir;
    this.deflaterFactory = deflaterFactory;
  }

  @Override
  public void applyDelta(File oldBlob, InputStream deltaIn, OutputStream newBlobOut)
      throws IOException {
    if (!tempDir.exists()) {
      // Be nice, try to create the temp directory. Don't bother to check return value as the code
      // will fail when it tries to create the file in a few more lines anyways.
      tempDir.mkdirs();
    }
    File tempFile = File.createTempFile("gfbfv1", "old", tempDir);
    try {
      applyDeltaInternal(oldBlob, tempFile, deltaIn, newBlobOut);
    } finally {
      tempFile.delete();
    }
  }

  /**
   * Does the work for applying a delta.
   * @param oldBlob the old blob
   * @param deltaFriendlyOldBlob the location in which to store the delta-friendly old blob
   * @param deltaIn the patch stream
   * @param newBlobOut the stream to write the new blob to after applying the delta
   * @throws IOException if anything goes wrong
   */
  private void applyDeltaInternal(
      File oldBlob, File deltaFriendlyOldBlob, InputStream deltaIn, OutputStream newBlobOut)
      throws IOException {

    // First, read the patch plan from the patch stream.
    PatchReader patchReader = new PatchReader();
    PatchApplyPlan plan = patchReader.readPatchApplyPlan(deltaIn);
    writeDeltaFriendlyOldBlob(plan, oldBlob, deltaFriendlyOldBlob);
    // Apply the delta. In v1 there is always exactly one delta descriptor, it is bsdiff, and it
    // takes up the rest of the patch stream - so there is no need to examine the list of
    // DeltaDescriptors in the patch at all.
    long deltaLength = plan.getDeltaDescriptors().get(0).getDeltaLength();
    DeltaApplier deltaApplier = getDeltaApplier();
    // Don't close this stream, as it is just a limiting wrapper.
    @SuppressWarnings("resource")
    LimitedInputStream limitedDeltaIn = new LimitedInputStream(deltaIn, deltaLength);
    // Don't close this stream, as it would close the underlying OutputStream (that we don't own).
    @SuppressWarnings("resource")
    PartiallyCompressingOutputStream recompressingNewBlobOut =
        new PartiallyCompressingOutputStream(
            plan.getDeltaFriendlyNewFileRecompressionPlan(),
            newBlobOut,
            DEFAULT_COPY_BUFFER_SIZE,
            deflaterFactory);
    deltaApplier.applyDelta(deltaFriendlyOldBlob, limitedDeltaIn, recompressingNewBlobOut);
    recompressingNewBlobOut.flush();
  }

  /**
   * Writes the delta-friendly old blob to temporary storage.
   * @param plan the plan to use for uncompressing
   * @param oldBlob the blob to turn into a delta-friendly blob
   * @param deltaFriendlyOldBlob where to write the blob
   * @throws IOException if anything goes wrong
   */
  private void writeDeltaFriendlyOldBlob(
      PatchApplyPlan plan, File oldBlob, File deltaFriendlyOldBlob) throws IOException {
    RandomAccessFileOutputStream deltaFriendlyOldFileOut = null;
    try {
      deltaFriendlyOldFileOut =
          new RandomAccessFileOutputStream(
              deltaFriendlyOldBlob, plan.getDeltaFriendlyOldFileSize());
      DeltaFriendlyFile.generateDeltaFriendlyFile(
          plan.getOldFileUncompressionPlan(),
          oldBlob,
          deltaFriendlyOldFileOut,
          false,
          DEFAULT_COPY_BUFFER_SIZE);
    } finally {
      try {
        deltaFriendlyOldFileOut.close();
      } catch (Exception ignored) {
        // Nothing
      }
    }
  }

  /**
   * Return an instance of a {@link DeltaApplier} suitable for applying the deltas within the patch
   * stream.
   * @return the applier
   */
  // Visible for testing only
  protected DeltaApplier getDeltaApplier() {
    return new BsDiffDeltaApplier();
  }
}