/*
    * 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
    *
    *      https://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.commons.io.input;
  
  import static org.apache.commons.io.IOUtils.EOF;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.OutputStreamWriter;
  import java.io.Reader;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.Charset;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CoderResult;
  import java.nio.charset.CodingErrorAction;
  
  import org.apache.commons.io.Charsets;
  import org.apache.commons.io.IOUtils;
  import org.apache.commons.io.build.AbstractStreamBuilder;
  import org.apache.commons.io.charset.CharsetEncoders;
  
  /**
   * {@link InputStream} implementation that reads a character stream from a {@link Reader} and transforms it to a byte stream using a specified charset encoding.
   * The stream is transformed using a {@link CharsetEncoder} object, guaranteeing that all charset encodings supported by the JRE are handled correctly. In
   * particular for charsets such as UTF-16, the implementation ensures that one and only one byte order marker is produced.
   * <p>
   * Since in general it is not possible to predict the number of characters to be read from the {@link Reader} to satisfy a read request on the
   * {@link ReaderInputStream}, all reads from the {@link Reader} are buffered. There is therefore no well defined correlation between the current position of the
   * {@link Reader} and that of the {@link ReaderInputStream}. This also implies that in general there is no need to wrap the underlying {@link Reader} in a
   * {@link BufferedReader}.
   * </p>
   * <p>
   * {@link ReaderInputStream} implements the inverse transformation of {@link InputStreamReader}; in the following example, reading from {@code in2}
   * would return the same byte sequence as reading from {@code in} (provided that the initial byte sequence is legal with respect to the charset encoding):
   * </p>
   * <p>
   * To build an instance, use {@link Builder}.
   * </p>
   * <pre>
   * InputStream inputStream = ...
   * Charset cs = ...
   * InputStreamReader reader = new InputStreamReader(inputStream, cs);
   * ReaderInputStream in2 = ReaderInputStream.builder()
   *   .setReader(reader)
   *   .setCharset(cs)
   *   .get();
   * </pre>
   * <p>
   * {@link ReaderInputStream} implements the same transformation as {@link OutputStreamWriter}, except that the control flow is reversed: both classes
   * transform a character stream into a byte stream, but {@link OutputStreamWriter} pushes data to the underlying stream, while {@link ReaderInputStream}
   * pulls it from the underlying stream.
   * </p>
   * <p>
   * Note that while there are use cases where there is no alternative to using this class, very often the need to use this class is an indication of a flaw in
   * the design of the code. This class is typically used in situations where an existing API only accepts an {@link InputStream}, but where the most natural way
   * to produce the data is as a character stream, by providing a {@link Reader} instance. An example of a situation where this problem may appear is when
   * implementing the {@code javax.activation.DataSource} interface from the Java Activation Framework.
   * </p>
   * <p>
   * The {@link #available()} method of this class always returns 0. The methods {@link #mark(int)} and {@link #reset()} are not supported.
   * </p>
   * <p>
   * Instances of {@link ReaderInputStream} are not thread safe.
   * </p>
   *
   * @see Builder
   * @see org.apache.commons.io.output.WriterOutputStream
   * @since 2.0
   */
  public class ReaderInputStream extends AbstractInputStream {
  
      // @formatter:off
      /**
       * Builds a new {@link ReaderInputStream}.
       *
       * <p>
       * For example:
       * </p>
       * <pre>{@code
       * ReaderInputStream s = ReaderInputStream.builder()
       *   .setPath(path)
       *   .setCharsetEncoder(Charset.defaultCharset().newEncoder())
      *   .get();}
      * </pre>
      *
      * @see #get()
      * @since 2.12.0
      */
     // @formatter:on
     public static class Builder extends AbstractStreamBuilder<ReaderInputStream, Builder> {
 
         private CharsetEncoder charsetEncoder = newEncoder(getCharset());
 
         /**
          * Constructs a new builder of {@link ReaderInputStream}.
          */
         public Builder() {
             // empty
         }
 
         /**
          * Builds a new {@link ReaderInputStream}.
          *
          * <p>
          * You must set an aspect that supports {@link #getReader()}, otherwise, this method throws an exception.
          * </p>
          * <p>
          * This builder uses the following aspects:
          * </p>
          * <ul>
          * <li>{@link #getReader()} gets the target aspect.</li>
          * <li>{@link #getBufferSize()}</li>
          * <li>{@link #getCharset()}</li>
          * <li>{@link CharsetEncoder}</li>
          * </ul>
          *
          * @return a new instance.
          * @throws UnsupportedOperationException if the origin cannot provide a {@link Reader}.
          * @throws IllegalStateException         if the {@code origin} is {@code null}.
          * @throws IOException                   if an I/O error occurs converting to a {@link Reader} using {@link #getReader()}.
          * @see #getReader()
          * @see CharsetEncoder
          * @see #getBufferSize()
          * @see #getUnchecked()
          */
         @Override
         public ReaderInputStream get() throws IOException {
             return new ReaderInputStream(this);
         }
 
         CharsetEncoder getCharsetEncoder() {
             return charsetEncoder;
         }
 
         @Override
         public Builder setCharset(final Charset charset) {
             super.setCharset(charset);
             charsetEncoder = newEncoder(getCharset());
             return this;
         }
 
         /**
          * Sets the charset encoder. Assumes that the caller has configured the encoder.
          *
          * @param newEncoder the charset encoder, null resets to a default encoder.
          * @return {@code this} instance.
          */
         public Builder setCharsetEncoder(final CharsetEncoder newEncoder) {
             charsetEncoder = CharsetEncoders.toCharsetEncoder(newEncoder, () -> newEncoder(getCharsetDefault()));
             super.setCharset(charsetEncoder.charset());
             return this;
         }
 
     }
 
     /**
      * Constructs a new {@link Builder}.
      *
      * @return a new {@link Builder}.
      * @since 2.12.0
      */
     public static Builder builder() {
         return new Builder();
     }
 
     static int checkMinBufferSize(final CharsetEncoder charsetEncoder, final int bufferSize) {
         final float minRequired = minBufferSize(charsetEncoder);
         if (bufferSize < minRequired) {
             throw new IllegalArgumentException(String.format("Buffer size %,d must be at least %s for a CharsetEncoder %s.", bufferSize, minRequired,
                     charsetEncoder.charset().displayName()));
         }
         return bufferSize;
     }
 
     static float minBufferSize(final CharsetEncoder charsetEncoder) {
         return charsetEncoder.maxBytesPerChar() * 2;
     }
 
     private static CharsetEncoder newEncoder(final Charset charset) {
         // @formatter:off
         return Charsets.toCharset(charset).newEncoder()
                 .onMalformedInput(CodingErrorAction.REPLACE)
                 .onUnmappableCharacter(CodingErrorAction.REPLACE);
         // @formatter:on
     }
 
     private final Reader reader;
 
     private final CharsetEncoder charsetEncoder;
 
     /**
      * CharBuffer used as input for the decoder. It should be reasonably large as we read data from the underlying Reader into this buffer.
      */
     private final CharBuffer encoderIn;
     /**
      * ByteBuffer used as output for the decoder. This buffer can be small as it is only used to transfer data from the decoder to the buffer provided by the
      * caller.
      */
     private final ByteBuffer encoderOut;
 
     private CoderResult lastCoderResult;
 
     private boolean endOfInput;
 
     @SuppressWarnings("resource") // caller closes.
     private ReaderInputStream(final Builder builder) throws IOException {
         this(builder.getReader(), builder.charsetEncoder, builder.getBufferSize());
     }
 
     /**
      * Constructs a new {@link ReaderInputStream} that uses the virtual machine's {@linkplain Charset#defaultCharset() default charset} with a default input
      * buffer size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
      *
      * @param reader the target {@link Reader}
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader) {
         this(reader, Charset.defaultCharset());
     }
 
     /**
      * Constructs a new {@link ReaderInputStream} with a default input buffer size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
      *
      * <p>
      * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
      * </p>
      *
      * @param reader  the target {@link Reader}
      * @param charset the charset encoding
      * @deprecated Use {@link ReaderInputStream#builder()} instead, will be protected for subclasses.
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final Charset charset) {
         this(reader, charset, IOUtils.DEFAULT_BUFFER_SIZE);
     }
 
     /**
      * Constructs a new {@link ReaderInputStream}.
      *
      * <p>
      * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
      * </p>
      *
      * @param reader     the target {@link Reader}.
      * @param charset    the charset encoding.
      * @param bufferSize the size of the input buffer in number of characters.
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final Charset charset, final int bufferSize) {
         // @formatter:off
         this(reader,
             Charsets.toCharset(charset).newEncoder()
                     .onMalformedInput(CodingErrorAction.REPLACE)
                     .onUnmappableCharacter(CodingErrorAction.REPLACE),
              bufferSize);
         // @formatter:on
     }
 
     /**
      * Constructs a new {@link ReaderInputStream}.
      *
      * <p>
      * This constructor does not call {@link CharsetEncoder#reset() reset} on the provided encoder. The caller of this constructor should do this when providing
      * an encoder which had already been in use.
      * </p>
      *
      * @param reader         the target {@link Reader}
      * @param charsetEncoder the charset encoder
      * @since 2.1
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final CharsetEncoder charsetEncoder) {
         this(reader, charsetEncoder, IOUtils.DEFAULT_BUFFER_SIZE);
     }
 
     /**
      * Constructs a new {@link ReaderInputStream}.
      *
      * <p>
      * This constructor does not call {@link CharsetEncoder#reset() reset} on the provided encoder. The caller of this constructor should do this when providing
      * an encoder which had already been in use.
      * </p>
      *
      * @param reader         the target {@link Reader}
      * @param charsetEncoder the charset encoder, null defaults to the default Charset encoder.
      * @param bufferSize     the size of the input buffer in number of characters
      * @since 2.1
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final CharsetEncoder charsetEncoder, final int bufferSize) {
         this.reader = reader;
         this.charsetEncoder = CharsetEncoders.toCharsetEncoder(charsetEncoder);
         this.encoderIn = CharBuffer.allocate(checkMinBufferSize(this.charsetEncoder, bufferSize));
         this.encoderIn.flip();
         this.encoderOut = ByteBuffer.allocate(128);
         this.encoderOut.flip();
     }
 
     /**
      * Constructs a new {@link ReaderInputStream} with a default input buffer size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
      *
      * <p>
      * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
      * </p>
      *
      * @param reader      the target {@link Reader}
      * @param charsetName the name of the charset encoding
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final String charsetName) {
         this(reader, charsetName, IOUtils.DEFAULT_BUFFER_SIZE);
     }
 
     /**
      * Constructs a new {@link ReaderInputStream}.
      *
      * <p>
      * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
      * </p>
      *
      * @param reader      the target {@link Reader}
      * @param charsetName the name of the charset encoding, null maps to the default Charset.
      * @param bufferSize  the size of the input buffer in number of characters
      * @deprecated Use {@link ReaderInputStream#builder()} instead
      */
     @Deprecated
     public ReaderInputStream(final Reader reader, final String charsetName, final int bufferSize) {
         this(reader, Charsets.toCharset(charsetName), bufferSize);
     }
 
     @Override
     public int available() throws IOException {
         if (encoderOut.hasRemaining()) {
             return encoderOut.remaining();
         }
         return 0;
     }
 
     /**
      * Closes the stream. This method will cause the underlying {@link Reader} to be closed.
      *
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public void close() throws IOException {
         reader.close();
         super.close();
     }
 
     /**
      * Fills the internal char buffer from the reader.
      *
      * @throws IOException If an I/O error occurs
      */
     private void fillBuffer() throws IOException {
         if (endOfInput) {
             return;
         }
         if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
             encoderIn.compact();
             final int position = encoderIn.position();
             // We don't use Reader#read(CharBuffer) here because it is more efficient
             // to write directly to the underlying char array (the default implementation
             // copies data to a temporary char array).
             final int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
             if (c == EOF) {
                 endOfInput = true;
             } else {
                 encoderIn.position(position + c);
             }
             encoderIn.flip();
         }
         encoderOut.compact();
         lastCoderResult = charsetEncoder.encode(encoderIn, encoderOut, endOfInput);
         if (endOfInput) {
             lastCoderResult = charsetEncoder.flush(encoderOut);
         }
         if (lastCoderResult.isError()) {
             lastCoderResult.throwException();
         }
         encoderOut.flip();
     }
 
     /**
      * Gets the CharsetEncoder.
      *
      * @return the CharsetEncoder.
      */
     CharsetEncoder getCharsetEncoder() {
         return charsetEncoder;
     }
 
     /**
      * Reads a single byte.
      *
      * @return either the byte read or {@code -1} if the end of the stream has been reached
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public int read() throws IOException {
         checkOpen();
         for (;;) {
             if (encoderOut.hasRemaining()) {
                 return encoderOut.get() & 0xFF;
             }
             fillBuffer();
             if (endOfInput && !encoderOut.hasRemaining()) {
                 return EOF;
             }
         }
     }
 
     /**
      * Reads the specified number of bytes into an array.
      *
      * @param b the byte array to read into, must not be {@code null}
      * @return the number of bytes read or {@code -1} if the end of the stream has been reached
      * @throws NullPointerException if the byte array is {@code null}.
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public int read(final byte[] b) throws IOException {
         return read(b, 0, b.length);
     }
 
     /**
      * Reads the specified number of bytes into an array.
      *
      * @param array the byte array to read into
      * @param off   the offset to start reading bytes into
      * @param len   the number of bytes to read
      * @return the number of bytes read or {@code -1} if the end of the stream has been reached
      * @throws NullPointerException      if the byte array is {@code null}.
      * @throws IndexOutOfBoundsException if {@code off} or {@code len} are negative, or if {@code off + len} is greater than {@code array.length}.
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public int read(final byte[] array, int off, int len) throws IOException {
         IOUtils.checkFromIndexSize(array, off, len);
         if (len == 0) {
             return 0; // Always return 0 if len == 0
         }
         int read = 0;
         while (len > 0) {
             if (encoderOut.hasRemaining()) { // Data from the last read not fully copied
                 final int c = Math.min(encoderOut.remaining(), len);
                 encoderOut.get(array, off, c);
                 off += c;
                 len -= c;
                 read += c;
             } else if (endOfInput) { // Already reach EOF in the last read
                 break;
             } else { // Read again
                 fillBuffer();
             }
         }
         return read == 0 && endOfInput ? EOF : read;
     }
 }