/*
    * 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.IOException;
  import java.io.InputStream;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.CharacterCodingException;
  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;
  import org.apache.commons.io.function.Uncheck;
  
  /**
   * Implements an {@link InputStream} to read bytes from String, StringBuffer, StringBuilder or CharBuffer,
   * encoded using the specified Charset. The Charset defaults to Charset.defaultCharset().
   * <p>
   * <strong>Note:</strong> Supports {@link #mark(int)} and {@link #reset()}.
   * </p>
   * <p>
   * To build an instance, use {@link Builder}.
   * </p>
   *
   * @see Builder
   * @since 2.2
   */
  public class CharSequenceInputStream extends InputStream {
  
      //@formatter:off
      /**
       * Builds a new {@link CharSequenceInputStream}.
       *
       * <p>
       * For example:
       * </p>
       * <h2>Using a Charset</h2>
       * <pre>{@code
       * CharSequenceInputStream s = CharSequenceInputStream.builder()
       *   .setBufferSize(8192)
       *   .setCharSequence("String")
       *   .setCharset(Charset.defaultCharset())
       *   .get();}
       * </pre>
       * <h2>Using a CharsetEncoder</h2>
       * <pre>{@code
       * CharSequenceInputStream s = CharSequenceInputStream.builder()
       *   .setBufferSize(8192)
       *   .setCharSequence("String")
       *   .setCharsetEncoder(Charset.defaultCharset().newEncoder()
       *     .onMalformedInput(CodingErrorAction.REPLACE)
       *     .onUnmappableCharacter(CodingErrorAction.REPLACE))
       *   .get();}
       * </pre>
       *
       * @see #get()
       * @since 2.13.0
       */
      //@formatter:on
      public static class Builder extends AbstractStreamBuilder<CharSequenceInputStream, Builder> {
  
          private CharsetEncoder charsetEncoder = newEncoder(getCharset());
  
          /**
           * Constructs a new builder of {@link CharSequenceInputStream}.
           */
          public Builder() {
              // empty
          }
  
          /**
           * Builds a new {@link CharSequenceInputStream}.
           * <p>
           * You must set an aspect that supports {@link #getCharSequence()}, otherwise, this method throws an exception.
           * </p>
           * <p>
          * This builder uses the following aspects:
          * </p>
          * <ul>
          * <li>{@link #getCharSequence()} gets the target aspect.</li>
          * <li>{@link #getBufferSize()}</li>
          * <li>{@link CharsetEncoder}</li>
          * </ul>
          *
          * @return a new instance.
          * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character.
          * @see #getUnchecked()
          */
         @Override
         public CharSequenceInputStream get() {
             return Uncheck.get(() -> new CharSequenceInputStream(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.
          * @return {@code this} instance.
          * @since 2.13.0
          */
         public Builder setCharsetEncoder(final CharsetEncoder newEncoder) {
             charsetEncoder = CharsetEncoders.toCharsetEncoder(newEncoder, () -> newEncoder(getCharsetDefault()));
             super.setCharset(charsetEncoder.charset());
             return this;
         }
 
     }
 
     private static final int NO_MARK = -1;
 
     /**
      * Constructs a new {@link Builder}.
      *
      * @return a new {@link Builder}.
      * @since 2.12.0
      */
     public static Builder builder() {
         return new Builder();
     }
 
     private static CharsetEncoder newEncoder(final Charset charset) {
         // @formatter:off
         return Charsets.toCharset(charset).newEncoder()
                 .onMalformedInput(CodingErrorAction.REPLACE)
                 .onUnmappableCharacter(CodingErrorAction.REPLACE);
         // @formatter:on
     }
 
     private final ByteBuffer bBuf;
     private int bBufMark; // position in bBuf
     private final CharBuffer cBuf;
     private int cBufMark; // position in cBuf
     private final CharsetEncoder charsetEncoder;
 
     private CharSequenceInputStream(final Builder builder) {
         this.charsetEncoder = builder.charsetEncoder;
         // Ensure that buffer is long enough to hold a complete character
         this.bBuf = ByteBuffer.allocate(ReaderInputStream.checkMinBufferSize(builder.charsetEncoder, builder.getBufferSize()));
         this.bBuf.flip();
         this.cBuf = CharBuffer.wrap(Uncheck.get(() -> builder.getCharSequence()));
         this.cBufMark = NO_MARK;
         this.bBufMark = NO_MARK;
         try {
             fillBuffer();
         } catch (final CharacterCodingException ex) {
             // Reset everything without filling the buffer
             // so the same exception can be thrown again later.
             this.bBuf.clear();
             this.bBuf.flip();
             this.cBuf.rewind();
         }
     }
 
     /**
      * Constructs a new instance with a buffer size of {@link IOUtils#DEFAULT_BUFFER_SIZE}.
      *
      * @param cs the input character sequence.
      * @param charset the character set name to use.
      * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character.
      * @deprecated Use {@link #builder()}, {@link Builder}, and {@link Builder#get()}
      */
     @Deprecated
     public CharSequenceInputStream(final CharSequence cs, final Charset charset) {
         this(cs, charset, IOUtils.DEFAULT_BUFFER_SIZE);
     }
 
     /**
      * Constructs a new instance.
      *
      * @param cs the input character sequence.
      * @param charset the character set name to use, null maps to the default Charset.
      * @param bufferSize the buffer size to use.
      * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character.
      * @deprecated Use {@link #builder()}, {@link Builder}, and {@link Builder#get()}
      */
     @Deprecated
     public CharSequenceInputStream(final CharSequence cs, final Charset charset, final int bufferSize) {
         this(builder().setCharSequence(cs).setCharset(charset).setBufferSize(bufferSize));
     }
 
     /**
      * Constructs a new instance with a buffer size of {@link IOUtils#DEFAULT_BUFFER_SIZE}.
      *
      * @param cs the input character sequence.
      * @param charset the character set name to use.
      * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character.
      * @deprecated Use {@link #builder()}, {@link Builder}, and {@link Builder#get()}
      */
     @Deprecated
     public CharSequenceInputStream(final CharSequence cs, final String charset) {
         this(cs, charset, IOUtils.DEFAULT_BUFFER_SIZE);
     }
 
     /**
      * Constructs a new instance.
      *
      * @param cs the input character sequence.
      * @param charset the character set name to use, null maps to the default Charset.
      * @param bufferSize the buffer size to use.
      * @throws IllegalArgumentException if the buffer is not large enough to hold a complete character.
      * @deprecated Use {@link #builder()}, {@link Builder}, and {@link Builder#get()}
      */
     @Deprecated
     public CharSequenceInputStream(final CharSequence cs, final String charset, final int bufferSize) {
         this(cs, Charsets.toCharset(charset), bufferSize);
     }
 
     /**
      * Gets a lower bound on the number of bytes remaining in the byte stream.
      *
      * @return the count of bytes that can be read without blocking (or returning EOF).
      * @throws IOException if an error occurs (probably not possible).
      */
     @Override
     public int available() throws IOException {
         return this.bBuf.remaining();
     }
 
     @Override
     public void close() throws IOException {
         bBuf.position(bBuf.limit());
     }
 
     /**
      * Fills the byte output buffer from the input char buffer.
      *
      * @throws CharacterCodingException
      *             an error encoding data.
      */
     private void fillBuffer() throws CharacterCodingException {
         this.bBuf.compact();
         final CoderResult result = this.charsetEncoder.encode(this.cBuf, this.bBuf, true);
         if (result.isError()) {
             result.throwException();
         }
         this.bBuf.flip();
     }
 
     /**
      * Gets the CharsetEncoder.
      *
      * @return the CharsetEncoder.
      */
     CharsetEncoder getCharsetEncoder() {
         return charsetEncoder;
     }
 
     /**
      * {@inheritDoc}
      * @param readLimit max read limit (ignored).
      */
     @Override
     public synchronized void mark(final int readLimit) {
         this.cBufMark = this.cBuf.position();
         this.bBufMark = this.bBuf.position();
         this.cBuf.mark();
         this.bBuf.mark();
         // It would be nice to be able to use mark & reset on the cBuf and bBuf;
         // however the bBuf is re-used so that won't work
     }
 
     @Override
     public boolean markSupported() {
         return true;
     }
 
     @Override
     public int read() throws IOException {
         for (;;) {
             if (this.bBuf.hasRemaining()) {
                 return this.bBuf.get() & 0xFF;
             }
             fillBuffer();
             if (!this.bBuf.hasRemaining() && !this.cBuf.hasRemaining()) {
                 return EOF;
             }
         }
     }
 
     @Override
     public int read(final byte[] b) throws IOException {
         return read(b, 0, b.length);
     }
 
     @Override
     public int read(final byte[] array, int off, int len) throws IOException {
         IOUtils.checkFromIndexSize(array, off, len);
         if (len == 0) {
             return 0; // must return 0 for zero length read
         }
         if (!this.bBuf.hasRemaining() && !this.cBuf.hasRemaining()) {
             return EOF;
         }
         int bytesRead = 0;
         while (len > 0) {
             if (this.bBuf.hasRemaining()) {
                 final int chunk = Math.min(this.bBuf.remaining(), len);
                 this.bBuf.get(array, off, chunk);
                 off += chunk;
                 len -= chunk;
                 bytesRead += chunk;
             } else {
                 fillBuffer();
                 if (!this.bBuf.hasRemaining() && !this.cBuf.hasRemaining()) {
                     break;
                 }
             }
         }
         return bytesRead == 0 && !this.cBuf.hasRemaining() ? EOF : bytesRead;
     }
 
     @Override
     public synchronized void reset() throws IOException {
         //
         // This is not the most efficient implementation, as it re-encodes from the beginning.
         //
         // Since the bBuf is re-used, in general it's necessary to re-encode the data.
         //
         // It should be possible to apply some optimizations however:
         // + use mark/reset on the cBuf and bBuf. This would only work if the buffer had not been (re)filled since
         // the mark. The code would have to catch InvalidMarkException - does not seem possible to check if mark is
         // valid otherwise. + Try saving the state of the cBuf before each fillBuffer; it might be possible to
         // restart from there.
         //
         if (this.cBufMark != NO_MARK) {
             // if cBuf is at 0, we have not started reading anything, so skip re-encoding
             if (this.cBuf.position() != 0) {
                 this.charsetEncoder.reset();
                 this.cBuf.rewind();
                 this.bBuf.rewind();
                 this.bBuf.limit(0); // rewind does not clear the buffer
                 while (this.cBuf.position() < this.cBufMark) {
                     this.bBuf.rewind(); // empty the buffer (we only refill when empty during normal processing)
                     this.bBuf.limit(0);
                     fillBuffer();
                 }
             }
             if (this.cBuf.position() != this.cBufMark) {
                 throw new IllegalStateException("Unexpected CharBuffer position: actual=" + cBuf.position() + " " +
                         "expected=" + this.cBufMark);
             }
             this.bBuf.position(this.bBufMark);
             this.cBufMark = NO_MARK;
             this.bBufMark = NO_MARK;
         }
         mark(0);
     }
 
     @Override
     public long skip(long n) throws IOException {
         //
         // This could be made more efficient by using position to skip within the current buffer.
         //
         long skipped = 0;
         while (n > 0 && available() > 0) {
             this.read();
             n--;
             skipped++;
         }
         return skipped;
     }
 
 }