/* Copyright 2002-2022 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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.orekit.data;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.Reader;
  import java.net.URI;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.StandardCharsets;
  import java.nio.file.Files;
  import java.nio.file.Paths;
  
  /** Container associating a name with a stream or reader that can be opened <em>lazily</em>.
   * <p>
   * This association and the lazy-opening are useful in different cases:
   * <ul>
   *   <li>when {@link DirectoryCrawler crawling} a directory tree to select data
   *   to be loaded by a {@link DataLoader}, the files that are not meaningful for
   *   the loader can be ignored and not opened at all</li>
   *   <li>when {@link DataFilter data filtering} is used, the raw stream can
   *   be opened by the filter only if the upper level filtered stream is opened</li>
   *   <li>when opening a stream for loading the data it provides, the opening
   *   and closing actions can be grouped in Orekit internal code using a {@code try
   *   with resources} clause so closing is done properly even in case of exception</li>
   *   <li>if some pre-reading of the first few bytes or characters are needed to decide how to
   *   load data (as in {@link org.orekit.files.ccsds.utils.lexical.LexicalAnalyzerSelector}),
   *   then the stream can be opened, buffered and rewound and a fake open method used
   *   to return the already open stream so a {@code try with resources} clause
   *   elsewhere works properly for closing the stream</li>
   * </ul>
   * <p>
   * Beware that the purpose of this class is only to delay this opening (or not open
   * the stream or reader at all), it is <em>not</em> intended to open the stream several
   * times and <em>not</em> intended to open both the binary stream and the characters reader.
   * Some implementations may fail if the {@link #getOpener() opener}'s
   * {@link Opener#openStreamOnce() openStreamOnce} or {@link Opener#openReaderOnce() openReaderOnce}
   * methods are called several times or are both called separately. This is particularly
   * true for network-based streams.
   * </p>
   * @see DataFilter
   * @author Luc Maisonobe
   * @since 9.2
   */
  public class DataSource {
  
      /** Name of the data (file name, zip entry name...). */
      private final String name;
  
      /** Supplier for data stream. */
      private final Opener opener;
  
      /** Complete constructor.
       * @param name data name
       * @param streamOpener opener for the data stream
       */
      public DataSource(final String name, final StreamOpener streamOpener) {
          this.name   = name;
          this.opener = new BinaryBasedOpener(streamOpener);
      }
  
      /** Complete constructor.
       * @param name data name
       * @param readerOpener opener for characters reader
       */
      public DataSource(final String name, final ReaderOpener readerOpener) {
          this.name   = name;
          this.opener = new ReaderBasedOpener(readerOpener);
      }
  
      /** Build an instance from file name only.
       * @param fileName name of the file
       * @since 11.0
       */
      public DataSource(final String fileName) {
          this(fileName, () -> Files.newInputStream(Paths.get(fileName)));
      }
  
      /** Build an instance from a file on the local file system.
       * @param file file
       * @since 11.0
      */
     public DataSource(final File file) {
         this(file.getName(), () -> new FileInputStream(file));
     }
 
     /** Build an instance from URI only.
      * @param uri URI of the file
      * @since 11.0
      */
     public DataSource(final URI uri) {
         this(Paths.get(uri).toFile());
     }
 
     /** Get the name of the data.
      * @return name of the data
      */
     public String getName() {
         return name;
     }
 
     /** Get the data stream opener.
      * @return data stream opener
      */
     public Opener getOpener() {
         return opener;
     }
 
     /** Interface for lazy-opening a binary stream one time. */
     public interface StreamOpener {
         /** Open the stream once.
          * <p>
          * Beware that this interface is only intended for <em>lazy</em> opening a
          * stream, i.e. to delay this opening (or not open the stream at all).
          * It is <em>not</em> intended to open the stream several times. Some
          * implementations may fail if an attempt to open a stream several
          * times is made. This is particularly true for network-based streams.
          * </p>
          * @return opened stream
          * @exception IOException if stream cannot be opened
          */
         InputStream openOnce() throws IOException;
 
     }
 
     /** Interface for lazy-opening a characters stream one time. */
     public interface ReaderOpener {
         /** Open the stream once.
          * <p>
          * Beware that this interface is only intended for <em>lazy</em> opening a
          * stream, i.e. to delay this opening (or not open the stream at all).
          * It is <em>not</em> intended to open the stream several times. Some
          * implementations may fail if an attempt to open a stream several
          * times is made. This is particularly true for network-based streams.
          * </p>
          * @return opened stream
          * @exception IOException if stream cannot be opened
          */
         Reader openOnce() throws IOException;
 
     }
 
     /** Interface for lazy-opening data streams one time. */
     public interface Opener {
 
         /** Check if the raw data is binary.
          * <p>
          * The raw data may be either binary or characters. In both cases,
          * either {@link #openStreamOnce()} or {@link #openReaderOnce()} may
          * be called, but one will be more efficient than the other as one
          * will supply data as is and the other one will convert raw data
          * before providing it. If conversion is needed, it will also be done
          * using {@link StandardCharsets#UTF_8 UTF8 encoding}, which may not
          * be suitable. This method helps the data consumer to either choose
          * the more efficient method or avoid wrong encoding conversion.
          * </p>
          * @return true if raw data is binary, false if raw data is characters
          */
         boolean rawDataIsBinary();
 
         /** Open a bytes stream once.
          * <p>
          * Beware that this interface is only intended for <em>lazy</em> opening a
          * stream, i.e. to delay this opening (or not open the stream at all).
          * It is <em>not</em> intended to open the stream several times and not
          * intended to open both the {@link #openStreamOnce() binary stream} and
          * the {@link #openReaderOnce() characters stream} separately (but opening
          * the reader may be implemented by opening the binary stream or vice-versa).
          * Implementations may fail if an attempt to open a stream several times is
          * made. This is particularly true for network-based streams.
          * </p>
          * @return opened stream or null if there are no data streams at all
          * @exception IOException if stream cannot be opened
          */
         InputStream openStreamOnce() throws IOException;
 
         /** Open a characters stream reader once.
          * <p>
          * Beware that this interface is only intended for <em>lazy</em> opening a
          * stream, i.e. to delay this opening (or not open the stream at all).
          * It is <em>not</em> intended to open the stream several times and not
          * intended to open both the {@link #openStreamOnce() binary stream} and
          * the {@link #openReaderOnce() characters stream} separately (but opening
          * the reader may be implemented by opening the binary stream or vice-versa).
          * Implementations may fail if an attempt to open a stream several times is
          * made. This is particularly true for network-based streams.
          * </p>
          * @return opened reader or null if there are no data streams at all
          * @exception IOException if stream cannot be opened
          */
         Reader openReaderOnce() throws IOException;
 
     }
 
     /** Opener based on a binary stream. */
     private static class BinaryBasedOpener implements Opener {
 
         /** Opener for the data stream. */
         private final StreamOpener streamOpener;
 
         /** Simple constructor.
          * @param streamOpener opener for the data stream
          */
         BinaryBasedOpener(final StreamOpener streamOpener) {
             this.streamOpener = streamOpener;
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean rawDataIsBinary() {
             return true;
         }
 
         /** {@inheritDoc} */
         @Override
         public InputStream openStreamOnce() throws IOException {
             return streamOpener.openOnce();
         }
 
         /** {@inheritDoc} */
         @Override
         public Reader openReaderOnce() throws IOException {
             // convert bytes to characters
             final InputStream is = openStreamOnce();
             return (is == null) ? null : new InputStreamReader(is, StandardCharsets.UTF_8);
         }
 
     }
 
     /** Opener based on a reader. */
     private static class ReaderBasedOpener implements Opener {
 
         /** Size of the characters buffer. */
         private static final int BUFFER_SIZE = 4096;
 
         /** Opener for characters reader. */
         private final ReaderOpener readerOpener;
 
         /** Simple constructor.
          * @param readerOpener opener for characters reader
          */
         ReaderBasedOpener(final ReaderOpener readerOpener) {
             this.readerOpener = readerOpener;
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean rawDataIsBinary() {
             return false;
         }
 
         /** {@inheritDoc} */
         @Override
         public InputStream openStreamOnce() throws IOException {
 
             // open the underlying reader
             final Reader reader = openReaderOnce();
             if (reader == null) {
                 return null;
             }
 
             // set up a stream that convert characters to bytes
             return new InputStream() {
 
                 private ByteBuffer buffer = null;
 
                 /** {@inheritDoc} */
                 @Override
                 public int read() throws IOException {
                     if (buffer == null || !buffer.hasRemaining()) {
                         // we need to refill the array
 
                         // get characters from the reader
                         final CharBuffer cb = CharBuffer.allocate(BUFFER_SIZE);
                         final int read = reader.read(cb);
                         if (read < 0) {
                             // end of data
                             return read;
                         }
 
                         // convert the characters read into bytes
                         final int last = cb.position();
                         cb.rewind();
                         buffer = StandardCharsets.UTF_8.encode(cb.subSequence(0, last));
 
                     }
 
                     // return next byte
                     return buffer.get();
 
                 }
 
             };
         }
 
         /** {@inheritDoc} */
         @Override
         public Reader openReaderOnce() throws IOException {
             return readerOpener.openOnce();
         }
 
     }
 
 }