/*
 * Licensed to the Apache Software Foundation (ASF) 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 org.apache.tsfile.external.commons.io.output;

import org.apache.tsfile.external.commons.io.IOUtils;
import org.apache.tsfile.external.commons.io.input.ClosedInputStream;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.SequenceInputStream;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static org.apache.tsfile.external.commons.io.IOUtils.EOF;

/**
 * This is the base class for implementing an output stream in which the data is written into a byte
 * array. The buffer automatically grows as data is written to it.
 *
 * <p>The data can be retrieved using {@code toByteArray()} and {@code toString()}. Closing an
 * {@link AbstractByteArrayOutputStream} has no effect. The methods in this class can be called
 * after the stream has been closed without generating an {@link IOException}.
 *
 * <p>This is the base for an alternative implementation of the {@link
 * java.io.ByteArrayOutputStream} class. The original implementation only allocates 32 bytes at the
 * beginning. As this class is designed for heavy duty it starts at {@value #DEFAULT_SIZE} bytes. In
 * contrast to the original it doesn't reallocate the whole memory block but allocates additional
 * buffers. This way no buffers need to be garbage collected and the contents don't have to be
 * copied to the new buffer. This class is designed to behave exactly like the original. The only
 * exception is the deprecated {@link java.io.ByteArrayOutputStream#toString(int)} method that has
 * been ignored.
 *
 * @since 2.7
 */
public abstract class AbstractByteArrayOutputStream extends OutputStream {

  /**
   * Constructor for an InputStream subclass.
   *
   * @param <T> the type of the InputStream.
   */
  @FunctionalInterface
  protected interface InputStreamConstructor<T extends InputStream> {

    /**
     * Constructs an InputStream subclass.
     *
     * @param buffer the buffer
     * @param offset the offset into the buffer
     * @param length the length of the buffer
     * @return the InputStream subclass.
     */
    T construct(final byte[] buffer, final int offset, final int length);
  }

  static final int DEFAULT_SIZE = 1024;

  /** The list of buffers, which grows and never reduces. */
  private final List<byte[]> buffers = new ArrayList<>();

  /** The index of the current buffer. */
  private int currentBufferIndex;

  /** The total count of bytes in all the filled buffers. */
  private int filledBufferSum;

  /** The current buffer. */
  private byte[] currentBuffer;

  /** The total count of bytes written. */
  protected int count;

  /** Flag to indicate if the buffers can be reused after reset */
  private boolean reuseBuffers = true;

  /**
   * Does nothing.
   *
   * <p>The methods in this class can be called after the stream has been closed without generating
   * an {@link IOException}.
   *
   * @throws IOException never (this method should not declare this exception but it has to now due
   *     to backwards compatibility)
   */
  @Override
  public void close() throws IOException {
    // nop
  }

  /**
   * Makes a new buffer available either by allocating a new one or re-cycling an existing one.
   *
   * @param newCount the size of the buffer if one is created
   */
  protected void needNewBuffer(final int newCount) {
    if (currentBufferIndex < buffers.size() - 1) {
      // Recycling old buffer
      filledBufferSum += currentBuffer.length;

      currentBufferIndex++;
      currentBuffer = buffers.get(currentBufferIndex);
    } else {
      // Creating new buffer
      final int newBufferSize;
      if (currentBuffer == null) {
        newBufferSize = newCount;
        filledBufferSum = 0;
      } else {
        newBufferSize = Math.max(currentBuffer.length << 1, newCount - filledBufferSum);
        filledBufferSum += currentBuffer.length;
      }

      currentBufferIndex++;
      currentBuffer = IOUtils.byteArray(newBufferSize);
      buffers.add(currentBuffer);
    }
  }

  /**
   * @see java.io.ByteArrayOutputStream#reset()
   */
  public abstract void reset();

  /**
   * @see java.io.ByteArrayOutputStream#reset()
   */
  protected void resetImpl() {
    count = 0;
    filledBufferSum = 0;
    currentBufferIndex = 0;
    if (reuseBuffers) {
      currentBuffer = buffers.get(currentBufferIndex);
    } else {
      // Throw away old buffers
      currentBuffer = null;
      final int size = buffers.get(0).length;
      buffers.clear();
      needNewBuffer(size);
      reuseBuffers = true;
    }
  }

  /**
   * Returns the current size of the byte array.
   *
   * @return the current size of the byte array
   */
  public abstract int size();

  /**
   * Gets the current contents of this byte stream as a byte array. The result is independent of
   * this stream.
   *
   * @return the current contents of this output stream, as a byte array
   * @see java.io.ByteArrayOutputStream#toByteArray()
   */
  public abstract byte[] toByteArray();

  /**
   * Gets the current contents of this byte stream as a byte array. The result is independent of
   * this stream.
   *
   * @return the current contents of this output stream, as a byte array
   * @see java.io.ByteArrayOutputStream#toByteArray()
   */
  protected byte[] toByteArrayImpl() {
    int remaining = count;
    if (remaining == 0) {
      return IOUtils.EMPTY_BYTE_ARRAY;
    }
    final byte[] newBuf = IOUtils.byteArray(remaining);
    int pos = 0;
    for (final byte[] buf : buffers) {
      final int c = Math.min(buf.length, remaining);
      System.arraycopy(buf, 0, newBuf, pos, c);
      pos += c;
      remaining -= c;
      if (remaining == 0) {
        break;
      }
    }
    return newBuf;
  }

  /**
   * Gets the current contents of this byte stream as an Input Stream. The returned stream is backed
   * by buffers of {@code this} stream, avoiding memory allocation and copy, thus saving space and
   * time.<br>
   *
   * @return the current contents of this output stream.
   * @see java.io.ByteArrayOutputStream#toByteArray()
   * @see #reset()
   * @since 2.5
   */
  public abstract InputStream toInputStream();

  /**
   * Gets the current contents of this byte stream as an Input Stream. The returned stream is backed
   * by buffers of {@code this} stream, avoiding memory allocation and copy, thus saving space and
   * time.<br>
   *
   * @param <T> the type of the InputStream which makes up the {@link SequenceInputStream}.
   * @param isConstructor A constructor for an InputStream which makes up the {@link
   *     SequenceInputStream}.
   * @return the current contents of this output stream.
   * @see java.io.ByteArrayOutputStream#toByteArray()
   * @see #reset()
   * @since 2.7
   */
  @SuppressWarnings("resource") // The result InputStream MUST be managed by the call site.
  protected <T extends InputStream> InputStream toInputStream(
      final InputStreamConstructor<T> isConstructor) {
    int remaining = count;
    if (remaining == 0) {
      return ClosedInputStream.INSTANCE;
    }
    final List<T> list = new ArrayList<>(buffers.size());
    for (final byte[] buf : buffers) {
      final int c = Math.min(buf.length, remaining);
      list.add(isConstructor.construct(buf, 0, c));
      remaining -= c;
      if (remaining == 0) {
        break;
      }
    }
    reuseBuffers = false;
    return new SequenceInputStream(Collections.enumeration(list));
  }

  /**
   * Gets the current contents of this byte stream as a string using the platform default charset.
   *
   * @return the contents of the byte array as a String
   * @see java.io.ByteArrayOutputStream#toString()
   * @deprecated 2.5 use {@link #toString(String)} instead
   */
  @Override
  @Deprecated
  public String toString() {
    // make explicit the use of the default charset
    return new String(toByteArray(), Charset.defaultCharset());
  }

  /**
   * Gets the current contents of this byte stream as a string using the specified encoding.
   *
   * @param charset the character encoding
   * @return the string converted from the byte array
   * @see java.io.ByteArrayOutputStream#toString(String)
   * @since 2.5
   */
  public String toString(final Charset charset) {
    return new String(toByteArray(), charset);
  }

  /**
   * Gets the current contents of this byte stream as a string using the specified encoding.
   *
   * @param enc the name of the character encoding
   * @return the string converted from the byte array
   * @throws UnsupportedEncodingException if the encoding is not supported
   * @see java.io.ByteArrayOutputStream#toString(String)
   */
  public String toString(final String enc) throws UnsupportedEncodingException {
    return new String(toByteArray(), enc);
  }

  @Override
  public abstract void write(final byte[] b, final int off, final int len);

  /**
   * Writes the entire contents of the specified input stream to this byte stream. Bytes from the
   * input stream are read directly into the internal buffer of this stream.
   *
   * @param in the input stream to read from
   * @return total number of bytes read from the input stream (and written to this stream)
   * @throws IOException if an I/O error occurs while reading the input stream
   * @since 1.4
   */
  public abstract int write(final InputStream in) throws IOException;

  @Override
  public abstract void write(final int b);

  /**
   * Writes the bytes to the byte array.
   *
   * @param b the bytes to write
   * @param off The start offset
   * @param len The number of bytes to write
   */
  protected void writeImpl(final byte[] b, final int off, final int len) {
    final int newCount = count + len;
    int remaining = len;
    int inBufferPos = count - filledBufferSum;
    while (remaining > 0) {
      final int part = Math.min(remaining, currentBuffer.length - inBufferPos);
      System.arraycopy(b, off + len - remaining, currentBuffer, inBufferPos, part);
      remaining -= part;
      if (remaining > 0) {
        needNewBuffer(newCount);
        inBufferPos = 0;
      }
    }
    count = newCount;
  }

  /**
   * Writes the entire contents of the specified input stream to this byte stream. Bytes from the
   * input stream are read directly into the internal buffer of this stream.
   *
   * @param in the input stream to read from
   * @return total number of bytes read from the input stream (and written to this stream)
   * @throws IOException if an I/O error occurs while reading the input stream
   * @since 2.7
   */
  protected int writeImpl(final InputStream in) throws IOException {
    int readCount = 0;
    int inBufferPos = count - filledBufferSum;
    int n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
    while (n != EOF) {
      readCount += n;
      inBufferPos += n;
      count += n;
      if (inBufferPos == currentBuffer.length) {
        needNewBuffer(currentBuffer.length);
        inBufferPos = 0;
      }
      n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
    }
    return readCount;
  }

  /**
   * Write a byte to byte array.
   *
   * @param b the byte to write
   */
  protected void writeImpl(final int b) {
    int inBufferPos = count - filledBufferSum;
    if (inBufferPos == currentBuffer.length) {
      needNewBuffer(count + 1);
      inBufferPos = 0;
    }
    currentBuffer[inBufferPos] = (byte) b;
    count++;
  }

  /**
   * Writes the entire contents of this byte stream to the specified output stream.
   *
   * @param out the output stream to write to
   * @throws IOException if an I/O error occurs, such as if the stream is closed
   * @see java.io.ByteArrayOutputStream#writeTo(OutputStream)
   */
  public abstract void writeTo(final OutputStream out) throws IOException;

  /**
   * Writes the entire contents of this byte stream to the specified output stream.
   *
   * @param out the output stream to write to
   * @throws IOException if an I/O error occurs, such as if the stream is closed
   * @see java.io.ByteArrayOutputStream#writeTo(OutputStream)
   */
  protected void writeToImpl(final OutputStream out) throws IOException {
    int remaining = count;
    for (final byte[] buf : buffers) {
      final int c = Math.min(buf.length, remaining);
      out.write(buf, 0, c);
      remaining -= c;
      if (remaining == 0) {
        break;
      }
    }
  }
}
