/*
 * Copyright (C) 2015 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.voicemail.impl.mail;

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

/**
 * A filtering InputStream that allows single byte "peeks" without consuming the byte. The client of
 * this stream can call peek() to see the next available byte in the stream and a subsequent read
 * will still return the peeked byte.
 */
public class PeekableInputStream extends InputStream {
  private final InputStream mIn;
  private boolean mPeeked;
  private int mPeekedByte;

  public PeekableInputStream(InputStream in) {
    this.mIn = in;
  }

  @Override
  public int read() throws IOException {
    if (!mPeeked) {
      return mIn.read();
    } else {
      mPeeked = false;
      return mPeekedByte;
    }
  }

  public int peek() throws IOException {
    if (!mPeeked) {
      mPeekedByte = read();
      mPeeked = true;
    }
    return mPeekedByte;
  }

  @Override
  public int read(byte[] b, int offset, int length) throws IOException {
    if (!mPeeked) {
      return mIn.read(b, offset, length);
    } else {
      b[0] = (byte) mPeekedByte;
      mPeeked = false;
      int r = mIn.read(b, offset + 1, length - 1);
      if (r == -1) {
        return 1;
      } else {
        return r + 1;
      }
    }
  }

  @Override
  public int read(byte[] b) throws IOException {
    return read(b, 0, b.length);
  }

  @Override
  public String toString() {
    return String.format(
        "PeekableInputStream(in=%s, peeked=%b, peekedByte=%d)",
        mIn.toString(), mPeeked, mPeekedByte);
  }
}