/*
 * Copyright (C) 2012 The Guava Authors
 *
 * 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.common.io;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.io.ByteStreams.createBuffer;
import static com.google.common.io.ByteStreams.skipUpTo;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Ascii;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableList;
import com.google.common.hash.Funnels;
import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.common.hash.Hasher;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.Reader;
import java.nio.charset.Charset;
import java.util.Arrays;
import java.util.Iterator;

/**
 * A readable source of bytes, such as a file. Unlike an {@link InputStream}, a {@code ByteSource}
 * is not an open, stateful stream for input that can be read and closed. Instead, it is an
 * immutable <i>supplier</i> of {@code InputStream} instances.
 *
 * <p>{@code ByteSource} provides two kinds of methods:
 * <ul>
 * <li><b>Methods that return a stream:</b> These methods should return a <i>new</i>, independent
 *     instance each time they are called. The caller is responsible for ensuring that the returned
 *     stream is closed.
 * <li><b>Convenience methods:</b> These are implementations of common operations that are typically
 *     implemented by opening a stream using one of the methods in the first category, doing
 *     something and finally closing the stream that was opened.
 * </ul>
 *
 * @since 14.0
 * @author Colin Decker
 */
@GwtIncompatible
public abstract class ByteSource {

  /**
   * Constructor for use by subclasses.
   */
  protected ByteSource() {}

  /**
   * Returns a {@link CharSource} view of this byte source that decodes bytes read from this source
   * as characters using the given {@link Charset}.
   *
   * <p>If {@link CharSource#asByteSource} is called on the returned source with the same charset,
   * the default implementation of this method will ensure that the original {@code ByteSource} is
   * returned, rather than round-trip encoding. Subclasses that override this method should behave
   * the same way.
   */
  public CharSource asCharSource(Charset charset) {
    return new AsCharSource(charset);
  }

  /**
   * Opens a new {@link InputStream} for reading from this source. This method should return a new,
   * independent stream each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned stream is closed.
   *
   * @throws IOException if an I/O error occurs in the process of opening the stream
   */
  public abstract InputStream openStream() throws IOException;

  /**
   * Opens a new buffered {@link InputStream} for reading from this source. The returned stream is
   * not required to be a {@link BufferedInputStream} in order to allow implementations to simply
   * delegate to {@link #openStream()} when the stream returned by that method does not benefit from
   * additional buffering (for example, a {@code ByteArrayInputStream}). This method should return a
   * new, independent stream each time it is called.
   *
   * <p>The caller is responsible for ensuring that the returned stream is closed.
   *
   * @throws IOException if an I/O error occurs in the process of opening the stream
   * @since 15.0 (in 14.0 with return type {@link BufferedInputStream})
   */
  public InputStream openBufferedStream() throws IOException {
    InputStream in = openStream();
    return (in instanceof BufferedInputStream)
        ? (BufferedInputStream) in
        : new BufferedInputStream(in);
  }

  /**
   * Returns a view of a slice of this byte source that is at most {@code length} bytes long
   * starting at the given {@code offset}. If {@code offset} is greater than the size of this
   * source, the returned source will be empty. If {@code offset + length} is greater than the size
   * of this source, the returned source will contain the slice starting at {@code offset} and
   * ending at the end of this source.
   *
   * @throws IllegalArgumentException if {@code offset} or {@code length} is negative
   */
  public ByteSource slice(long offset, long length) {
    return new SlicedByteSource(offset, length);
  }

  /**
   * Returns whether the source has zero bytes. The default implementation returns true if
   * {@link #sizeIfKnown} returns zero, falling back to opening a stream and checking for EOF if the
   * size is not known.
   *
   * <p>Note that, in cases where {@code sizeIfKnown} returns zero, it is <i>possible</i> that bytes
   * are actually available for reading. (For example, some special files may return a size of 0
   * despite actually having content when read.) This means that a source may return {@code true}
   * from {@code isEmpty()} despite having readable content.
   *
   * @throws IOException if an I/O error occurs
   * @since 15.0
   */
  public boolean isEmpty() throws IOException {
    Optional<Long> sizeIfKnown = sizeIfKnown();
    if (sizeIfKnown.isPresent() && sizeIfKnown.get() == 0L) {
      return true;
    }
    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return in.read() == -1;
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Returns the size of this source in bytes, if the size can be easily determined without actually
   * opening the data stream.
   *
   * <p>The default implementation returns {@link Optional#absent}. Some sources, such as a file,
   * may return a non-absent value. Note that in such cases, it is <i>possible</i> that this method
   * will return a different number of bytes than would be returned by reading all of the bytes (for
   * example, some special files may return a size of 0 despite actually having content when read).
   *
   * <p>Additionally, for mutable sources such as files, a subsequent read may return a different
   * number of bytes if the contents are changed.
   *
   * @since 19.0
   */
  @Beta
  public Optional<Long> sizeIfKnown() {
    return Optional.absent();
  }

  /**
   * Returns the size of this source in bytes, even if doing so requires opening and traversing an
   * entire stream. To avoid a potentially expensive operation, see {@link #sizeIfKnown}.
   *
   * <p>The default implementation calls {@link #sizeIfKnown} and returns the value if present. If
   * absent, it will fall back to a heavyweight operation that will open a stream, read (or
   * {@link InputStream#skip(long) skip}, if possible) to the end of the stream and return the total
   * number of bytes that were read.
   *
   * <p>Note that for some sources that implement {@link #sizeIfKnown} to provide a more efficient
   * implementation, it is <i>possible</i> that this method will return a different number of bytes
   * than would be returned by reading all of the bytes (for example, some special files may return
   * a size of 0 despite actually having content when read).
   *
   * <p>In either case, for mutable sources such as files, a subsequent read may return a different
   * number of bytes if the contents are changed.
   *
   * @throws IOException if an I/O error occurs in the process of reading the size of this source
   */
  public long size() throws IOException {
    Optional<Long> sizeIfKnown = sizeIfKnown();
    if (sizeIfKnown.isPresent()) {
      return sizeIfKnown.get();
    }

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return countBySkipping(in);
    } catch (IOException e) {
      // skip may not be supported... at any rate, try reading
    } finally {
      closer.close();
    }

    closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return ByteStreams.exhaust(in);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Counts the bytes in the given input stream using skip if possible. Returns SKIP_FAILED if the
   * first call to skip threw, in which case skip may just not be supported.
   */
  private long countBySkipping(InputStream in) throws IOException {
    long count = 0;
    long skipped;
    while ((skipped = skipUpTo(in, Integer.MAX_VALUE)) > 0) {
      count += skipped;
    }
    return count;
  }

  /**
   * Copies the contents of this byte source to the given {@code OutputStream}. Does not close
   * {@code output}.
   *
   * @return the number of bytes copied
   * @throws IOException if an I/O error occurs in the process of reading from this source or
   *     writing to {@code output}
   */
  @CanIgnoreReturnValue
  public long copyTo(OutputStream output) throws IOException {
    checkNotNull(output);

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return ByteStreams.copy(in, output);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Copies the contents of this byte source to the given {@code ByteSink}.
   *
   * @return the number of bytes copied
   * @throws IOException if an I/O error occurs in the process of reading from this source or
   *     writing to {@code sink}
   */
  @CanIgnoreReturnValue
  public long copyTo(ByteSink sink) throws IOException {
    checkNotNull(sink);

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      OutputStream out = closer.register(sink.openStream());
      return ByteStreams.copy(in, out);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads the full contents of this byte source as a byte array.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source
   */
  public byte[] read() throws IOException {
    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return ByteStreams.toByteArray(in);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Reads the contents of this byte source using the given {@code processor} to process bytes as
   * they are read. Stops when all bytes have been read or the consumer returns {@code false}.
   * Returns the result produced by the processor.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source or if
   *     {@code processor} throws an {@code IOException}
   * @since 16.0
   */
  @Beta
  @CanIgnoreReturnValue // some processors won't return a useful result
  public <T> T read(ByteProcessor<T> processor) throws IOException {
    checkNotNull(processor);

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(openStream());
      return ByteStreams.readBytes(in, processor);
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Hashes the contents of this byte source using the given hash function.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source
   */
  public HashCode hash(HashFunction hashFunction) throws IOException {
    Hasher hasher = hashFunction.newHasher();
    copyTo(Funnels.asOutputStream(hasher));
    return hasher.hash();
  }

  /**
   * Checks that the contents of this byte source are equal to the contents of the given byte
   * source.
   *
   * @throws IOException if an I/O error occurs in the process of reading from this source or
   *     {@code other}
   */
  public boolean contentEquals(ByteSource other) throws IOException {
    checkNotNull(other);

    byte[] buf1 = createBuffer();
    byte[] buf2 = createBuffer();

    Closer closer = Closer.create();
    try {
      InputStream in1 = closer.register(openStream());
      InputStream in2 = closer.register(other.openStream());
      while (true) {
        int read1 = ByteStreams.read(in1, buf1, 0, buf1.length);
        int read2 = ByteStreams.read(in2, buf2, 0, buf2.length);
        if (read1 != read2 || !Arrays.equals(buf1, buf2)) {
          return false;
        } else if (read1 != buf1.length) {
          return true;
        }
      }
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * @param sources the sources to concatenate
   * @return a {@code ByteSource} containing the concatenated data
   * @since 15.0
   */
  public static ByteSource concat(Iterable<? extends ByteSource> sources) {
    return new ConcatenatedByteSource(sources);
  }

  /**
   * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this method
   * is called. This will fail if the iterator is infinite and may cause problems if the iterator
   * eagerly fetches data for each source when iterated (rather than producing sources that only
   * load data through their streams). Prefer using the {@link #concat(Iterable)} overload if
   * possible.
   *
   * @param sources the sources to concatenate
   * @return a {@code ByteSource} containing the concatenated data
   * @throws NullPointerException if any of {@code sources} is {@code null}
   * @since 15.0
   */
  public static ByteSource concat(Iterator<? extends ByteSource> sources) {
    return concat(ImmutableList.copyOf(sources));
  }

  /**
   * Concatenates multiple {@link ByteSource} instances into a single source. Streams returned from
   * the source will contain the concatenated data from the streams of the underlying sources.
   *
   * <p>Only one underlying stream will be open at a time. Closing the concatenated stream will
   * close the open underlying stream.
   *
   * @param sources the sources to concatenate
   * @return a {@code ByteSource} containing the concatenated data
   * @throws NullPointerException if any of {@code sources} is {@code null}
   * @since 15.0
   */
  public static ByteSource concat(ByteSource... sources) {
    return concat(ImmutableList.copyOf(sources));
  }

  /**
   * Returns a view of the given byte array as a {@link ByteSource}. To view only a specific range
   * in the array, use {@code ByteSource.wrap(b).slice(offset, length)}.
   *
   * @since 15.0 (since 14.0 as {@code ByteStreams.asByteSource(byte[])}).
   */
  public static ByteSource wrap(byte[] b) {
    return new ByteArrayByteSource(b);
  }

  /**
   * Returns an immutable {@link ByteSource} that contains no bytes.
   *
   * @since 15.0
   */
  public static ByteSource empty() {
    return EmptyByteSource.INSTANCE;
  }

  /**
   * A char source that reads bytes from this source and decodes them as characters using a charset.
   */
  private final class AsCharSource extends CharSource {

    final Charset charset;

    AsCharSource(Charset charset) {
      this.charset = checkNotNull(charset);
    }

    @Override
    public ByteSource asByteSource(Charset charset) {
      if (charset.equals(this.charset)) {
        return ByteSource.this;
      }
      return super.asByteSource(charset);
    }

    @Override
    public Reader openStream() throws IOException {
      return new InputStreamReader(ByteSource.this.openStream(), charset);
    }

    @Override
    public String toString() {
      return ByteSource.this.toString() + ".asCharSource(" + charset + ")";
    }
  }

  /**
   * A view of a subsection of the containing byte source.
   */
  private final class SlicedByteSource extends ByteSource {

    final long offset;
    final long length;

    SlicedByteSource(long offset, long length) {
      checkArgument(offset >= 0, "offset (%s) may not be negative", offset);
      checkArgument(length >= 0, "length (%s) may not be negative", length);
      this.offset = offset;
      this.length = length;
    }

    @Override
    public InputStream openStream() throws IOException {
      return sliceStream(ByteSource.this.openStream());
    }

    @Override
    public InputStream openBufferedStream() throws IOException {
      return sliceStream(ByteSource.this.openBufferedStream());
    }

    private InputStream sliceStream(InputStream in) throws IOException {
      if (offset > 0) {
        long skipped;
        try {
          skipped = ByteStreams.skipUpTo(in, offset);
        } catch (Throwable e) {
          Closer closer = Closer.create();
          closer.register(in);
          try {
            throw closer.rethrow(e);
          } finally {
            closer.close();
          }
        }

        if (skipped < offset) {
          // offset was beyond EOF
          in.close();
          return new ByteArrayInputStream(new byte[0]);
        }
      }
      return ByteStreams.limit(in, length);
    }

    @Override
    public ByteSource slice(long offset, long length) {
      checkArgument(offset >= 0, "offset (%s) may not be negative", offset);
      checkArgument(length >= 0, "length (%s) may not be negative", length);
      long maxLength = this.length - offset;
      return ByteSource.this.slice(this.offset + offset, Math.min(length, maxLength));
    }

    @Override
    public boolean isEmpty() throws IOException {
      return length == 0 || super.isEmpty();
    }

    @Override
    public Optional<Long> sizeIfKnown() {
      Optional<Long> optionalUnslicedSize = ByteSource.this.sizeIfKnown();
      if (optionalUnslicedSize.isPresent()) {
        long unslicedSize = optionalUnslicedSize.get();
        long off = Math.min(offset, unslicedSize);
        return Optional.of(Math.min(length, unslicedSize - off));
      }
      return Optional.absent();
    }

    @Override
    public String toString() {
      return ByteSource.this.toString() + ".slice(" + offset + ", " + length + ")";
    }
  }

  private static class ByteArrayByteSource extends ByteSource {

    final byte[] bytes;
    final int offset;
    final int length;

    ByteArrayByteSource(byte[] bytes) {
      this(bytes, 0, bytes.length);
    }

    // NOTE: Preconditions are enforced by slice, the only non-trivial caller.
    ByteArrayByteSource(byte[] bytes, int offset, int length) {
      this.bytes = bytes;
      this.offset = offset;
      this.length = length;
    }

    @Override
    public InputStream openStream() {
      return new ByteArrayInputStream(bytes, offset, length);
    }

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

    @Override
    public boolean isEmpty() {
      return length == 0;
    }

    @Override
    public long size() {
      return length;
    }

    @Override
    public Optional<Long> sizeIfKnown() {
      return Optional.of((long) length);
    }

    @Override
    public byte[] read() {
      return Arrays.copyOfRange(bytes, offset, offset + length);
    }

    @Override
    public long copyTo(OutputStream output) throws IOException {
      output.write(bytes, offset, length);
      return length;
    }

    @SuppressWarnings("CheckReturnValue") // it doesn't matter what processBytes returns here
    @Override
    public <T> T read(ByteProcessor<T> processor) throws IOException {
      processor.processBytes(bytes, offset, length);
      return processor.getResult();
    }

    @Override
    public HashCode hash(HashFunction hashFunction) throws IOException {
      return hashFunction.hashBytes(bytes, offset, length);
    }

    @Override
    public ByteSource slice(long offset, long length) {
      checkArgument(offset >= 0, "offset (%s) may not be negative", offset);
      checkArgument(length >= 0, "length (%s) may not be negative", length);

      offset = Math.min(offset, this.length);
      length = Math.min(length, this.length - offset);
      int newOffset = this.offset + (int) offset;
      return new ByteArrayByteSource(bytes, newOffset, (int) length);
    }

    @Override
    public String toString() {
      return "ByteSource.wrap("
          + Ascii.truncate(BaseEncoding.base16().encode(bytes, offset, length), 30, "...") + ")";
    }
  }

  private static final class EmptyByteSource extends ByteArrayByteSource {

    static final EmptyByteSource INSTANCE = new EmptyByteSource();

    EmptyByteSource() {
      super(new byte[0]);
    }

    @Override
    public CharSource asCharSource(Charset charset) {
      checkNotNull(charset);
      return CharSource.empty();
    }

    @Override
    public byte[] read() {
      return bytes; // length is 0, no need to clone
    }

    @Override
    public String toString() {
      return "ByteSource.empty()";
    }
  }

  private static final class ConcatenatedByteSource extends ByteSource {

    final Iterable<? extends ByteSource> sources;

    ConcatenatedByteSource(Iterable<? extends ByteSource> sources) {
      this.sources = checkNotNull(sources);
    }

    @Override
    public InputStream openStream() throws IOException {
      return new MultiInputStream(sources.iterator());
    }

    @Override
    public boolean isEmpty() throws IOException {
      for (ByteSource source : sources) {
        if (!source.isEmpty()) {
          return false;
        }
      }
      return true;
    }

    @Override
    public Optional<Long> sizeIfKnown() {
      long result = 0L;
      for (ByteSource source : sources) {
        Optional<Long> sizeIfKnown = source.sizeIfKnown();
        if (!sizeIfKnown.isPresent()) {
          return Optional.absent();
        }
        result += sizeIfKnown.get();
      }
      return Optional.of(result);
    }

    @Override
    public long size() throws IOException {
      long result = 0L;
      for (ByteSource source : sources) {
        result += source.size();
      }
      return result;
    }

    @Override
    public String toString() {
      return "ByteSource.concat(" + sources + ")";
    }
  }
}
