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/*
 * Licensed to the University of California, Berkeley under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional information regarding
 * copyright ownership. The ASF licenses this file to You 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 tachyon.client.file;

import java.io.IOException;
import java.io.InputStream;

import tachyon.client.ClientContext;
import tachyon.client.block.BlockInStream;
import tachyon.underfs.UnderFileSystem;

/**
 * This class provides a streaming API to read a fixed chunk from a file in the under storage
 * system. The user may freely seek and skip within the fixed chunk of data. The under storage
 * system read does not guarantee any locality and is dependent on the implementation of the under
 * storage client.
 */
// TODO(calvin): This should be treated like a block in stream.
public final class UnderStoreFileInStream extends BlockInStream {
  private final long mInitPos;
  private final long mLength;
  private final String mUfsPath;

  private long mPos;
  private InputStream mUnderStoreStream;

  /**
   * Creates a new under storage file input stream.
   *
   * @param initPos the initial position
   * @param length the length
   * @param ufsPath the under file system path
   * @throws IOException if an I/O error occurs
   */
  public UnderStoreFileInStream(long initPos, long length, String ufsPath) throws IOException {
    mInitPos = initPos;
    mLength = length;
    mUfsPath = ufsPath;
    setUnderStoreStream(initPos);
  }

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

  @Override
  public int read() throws IOException {
    int data = mUnderStoreStream.read();
    mPos ++;
    return data;
  }

  @Override
  public int read(byte[] b) throws IOException {
    int data = mUnderStoreStream.read(b);
    mPos ++;
    return data;
  }

  @Override
  public int read(byte[] b, int off, int len) throws IOException {
    int bytesRead = mUnderStoreStream.read(b, off, len);
    mPos += bytesRead;
    return bytesRead;
  }

  @Override
  public long remaining() {
    return mInitPos + mLength - mPos;
  }

  @Override
  public void seek(long pos) throws IOException {
    long offset = mPos - mInitPos;
    if (pos < offset) {
      setUnderStoreStream(pos);
    } else {
      long toSkip = pos - offset;
      if (skip(toSkip) != toSkip) {
        throw new IOException("Failed to seek forward to " + pos);
      }
    }
  }

  @Override
  public long skip(long n) throws IOException {
    // Negative skip returns 0
    if (n <= 0) {
      return 0;
    }
    // Cannot skip beyond boundary
    long toSkip = Math.min(mInitPos + mLength - mPos, n);
    long skipped = mUnderStoreStream.skip(toSkip);
    if (toSkip != skipped) {
      throw new IOException("Failed to skip " + toSkip);
    }
    mPos += skipped;
    return skipped;
  }

  private void setUnderStoreStream(long pos) throws IOException {
    if (mUnderStoreStream != null) {
      mUnderStoreStream.close();
    }
    UnderFileSystem ufs = UnderFileSystem.get(mUfsPath, ClientContext.getConf());
    mUnderStoreStream = ufs.open(mUfsPath);
    mPos = 0;
    if (pos != skip(pos)) {
      throw new IOException("Failed to skip: " + pos);
    }
  }
}