/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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.android.tools.build.apkzlib.zip;

import com.android.tools.build.apkzlib.zip.utils.CloseableByteSource;
import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.common.io.ByteProcessor;
import com.google.common.io.ByteSink;
import com.google.common.io.ByteSource;
import com.google.common.io.CharSource;
import com.google.common.util.concurrent.ListenableFuture;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.charset.Charset;
import java.util.concurrent.ExecutionException;

/**
 * {@code ByteSource} that delegates all operations to another {@code ByteSource}. The other byte
 * source, the <em>delegate</em>, may be computed lazily.
 */
public class LazyDelegateByteSource extends CloseableByteSource {

  /** Byte source where we delegate operations to. */
  private final ListenableFuture<CloseableByteSource> delegate;

  /**
   * Creates a new byte source that delegates operations to the provided source.
   *
   * @param delegate the source that will receive all operations
   */
  public LazyDelegateByteSource(ListenableFuture<CloseableByteSource> delegate) {
    this.delegate = delegate;
  }

  /**
   * Obtains the delegate future.
   *
   * @return the delegate future, that may be computed or not
   */
  public ListenableFuture<CloseableByteSource> getDelegate() {
    return delegate;
  }

  /**
   * Obtains the byte source, waiting for the future to be computed.
   *
   * @return the byte source
   * @throws IOException failed to compute the future :)
   */
  private CloseableByteSource get() throws IOException {
    try {
      CloseableByteSource r = delegate.get();
      if (r == null) {
        throw new IOException("Delegate byte source computation resulted in null.");
      }

      return r;
    } catch (InterruptedException e) {
      throw new IOException("Interrupted while waiting for byte source computation.", e);
    } catch (ExecutionException e) {
      throw new IOException("Failed to compute byte source.", e);
    }
  }

  @Override
  public CharSource asCharSource(Charset charset) {
    try {
      return get().asCharSource(charset);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  @Override
  public InputStream openBufferedStream() throws IOException {
    return get().openBufferedStream();
  }

  @Override
  public ByteSource slice(long offset, long length) {
    try {
      return get().slice(offset, length);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  @Override
  public boolean isEmpty() throws IOException {
    return get().isEmpty();
  }

  @Override
  public long size() throws IOException {
    return get().size();
  }

  @Override
  public long copyTo(OutputStream output) throws IOException {
    return get().copyTo(output);
  }

  @Override
  public long copyTo(ByteSink sink) throws IOException {
    return get().copyTo(sink);
  }

  @Override
  public byte[] read() throws IOException {
    return get().read();
  }

  @Override
  public <T> T read(ByteProcessor<T> processor) throws IOException {
    return get().read(processor);
  }

  @Override
  public HashCode hash(HashFunction hashFunction) throws IOException {
    return get().hash(hashFunction);
  }

  @Override
  public boolean contentEquals(ByteSource other) throws IOException {
    return get().contentEquals(other);
  }

  @Override
  public InputStream openStream() throws IOException {
    return get().openStream();
  }

  @Override
  public void innerClose() throws IOException {
    get().close();
  }
}