/*
    * 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.net.ftp;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.stream.Collectors;
  
  import org.apache.commons.io.Charsets;
  
  
  /**
   * This class handles the entire process of parsing a listing of file entries from the server.
   * <p>
   * This object defines a two-part parsing mechanism.
   * </p>
   * <p>
   * The first part consists of reading the raw input into an internal list of strings. Every item in this list corresponds to an actual file. All extraneous
   * matter emitted by the server will have been removed by the end of this phase. This is accomplished in conjunction with the FTPFileEntryParser associated with
   * this engine, by calling its methods {@code readNextEntry()} - which handles the issue of what delimits one entry from another, usually but not always a line
   * feed and {@code preParse()} - which handles removal of extraneous matter such as the preliminary lines of a listing, removal of duplicates on versioning
   * systems, etc.
   * </p>
   * <p>
   * The second part is composed of the actual parsing, again in conjunction with the particular parser used by this engine. This is controlled by an iterator
   * over the internal list of strings. This may be done either in block mode, by calling the {@code getNext()} and {@code getPrevious()} methods to provide
   * "paged" output of less than the whole list at one time, or by calling the {@code getFiles()} method to return the entire list.
   * </p>
   * <p>
   * Examples:
   * </p>
   * <p>
   * Paged access:
   * </p>
   * <pre>
   * FTPClient f = FTPClient();
   * f.connect(server);
   * f.login(user, password);
   * FTPListParseEngine engine = f.initiateListParsing(directory);
   *
   * while (engine.hasNext()) {
   *     FTPFile[] files = engine.getNext(25); // "page size" you want
   *     // do whatever you want with these files, display them, etc.
   *     // expensive FTPFile objects not created until needed.
   * }
   * </pre>
   * <p>
   * For unpaged access, simply use FTPClient.listFiles(). That method uses this class transparently.
   * </p>
   */
  public class FTPListParseEngine {
  
      /**
       * An empty immutable {@code FTPFile} array.
       */
      private static final FTPFile[] EMPTY_FTP_FILE_ARRAY = {};
      private List<String> entries = new LinkedList<>();
  
      private ListIterator<String> internalIterator = entries.listIterator();
      private final FTPFileEntryParser parser;
  
      // Should invalid files (parse failures) be allowed?
      private final boolean saveUnparseableEntries;
  
      /**
       * Constructs a new instance.
       *
       * @param parser How to parse file entries.
       */
      public FTPListParseEngine(final FTPFileEntryParser parser) {
          this(parser, null);
      }
  
      /**
       * Intended for use by FTPClient only
       *
       * @since 3.4
       */
      FTPListParseEngine(final FTPFileEntryParser parser, final FTPClientConfig configuration) {
         this.parser = parser;
         this.saveUnparseableEntries = configuration != null && configuration.getUnparseableEntries();
     }
 
     /**
      * Gets a list of FTPFile objects containing the whole list of files returned by the server as read by this object's parser. The files are filtered
      * before being added to the array.
      *
      * @param filter FTPFileFilter, must not be {@code null}.
      * @return a list of FTPFile objects containing the whole list of files returned by the server as read by this object's parser.
      *         <p>
      *         <strong> NOTE:</strong> This array may contain null members if any of the individual file listings failed to parse. The caller should check each
      *         entry for null before referencing it, or use a filter such as {@link FTPFileFilters#NON_NULL} which does not allow null entries.
      * @since 3.9.0
      */
     public List<FTPFile> getFileList(final FTPFileFilter filter) {
         return entries.stream().map(e -> {
             final FTPFile file = parser.parseFTPEntry(e);
             return file == null && saveUnparseableEntries ? new FTPFile(e) : file;
         }).filter(filter::accept).collect(Collectors.toList());
     }
 
     /**
      * Gets an array of FTPFile objects containing the whole list of files returned by the server as read by this object's parser.
      *
      * @return an array of FTPFile objects containing the whole list of files returned by the server as read by this object's parser. None of the entries will
      *         be null
      * @throws IOException - not ever thrown, may be removed in a later release
      */
     // TODO remove; not actually thrown
     public FTPFile[] getFiles() throws IOException {
         return getFiles(FTPFileFilters.NON_NULL);
     }
 
     /**
      * Gets an array of FTPFile objects containing the whole list of files returned by the server as read by this object's parser. The files are filtered
      * before being added to the array.
      *
      * @param filter FTPFileFilter, must not be {@code null}.
      * @return an array of FTPFile objects containing the whole list of files returned by the server as read by this object's parser.
      *         <p>
      *         <strong> NOTE:</strong> This array may contain null members if any of the individual file listings failed to parse. The caller should check each
      *         entry for null before referencing it, or use a filter such as {@link FTPFileFilters#NON_NULL} which does not allow null entries.
      * @throws IOException - not ever thrown, may be removed in a later release
      * @since 2.2
      */
     // TODO remove; not actually thrown
     public FTPFile[] getFiles(final FTPFileFilter filter) throws IOException {
         return getFileList(filter).toArray(EMPTY_FTP_FILE_ARRAY);
     }
 
     /**
      * Gets an array of at most {@code quantityRequested} FTPFile objects starting at this object's internal iterator's current position. If fewer than
      * {@code quantityRequested} such elements are available, the returned array will have a length equal to the number of entries at and after the current
      * position. If no such entries are found, this array will have a length of 0.
      *
      * After this method is called this object's internal iterator is advanced by a number of positions equal to the size of the array returned.
      *
      * @param quantityRequested the maximum number of entries we want to get.
      * @return an array of at most {@code quantityRequested} FTPFile objects starting at the current position of this iterator within its list and at least the
      *         number of elements which exist in the list at and after its current position.
      *         <p>
      *         <strong> NOTE:</strong> This array may contain null members if any of the individual file listings failed to parse. The caller should check each
      *         entry for null before referencing it.
      */
     public FTPFile[] getNext(final int quantityRequested) {
         final List<FTPFile> tmpResults = new LinkedList<>();
         int count = quantityRequested;
         while (count > 0 && internalIterator.hasNext()) {
             final String entry = internalIterator.next();
             FTPFile temp = parser.parseFTPEntry(entry);
             if (temp == null && saveUnparseableEntries) {
                 temp = new FTPFile(entry);
             }
             tmpResults.add(temp);
             count--;
         }
         return tmpResults.toArray(EMPTY_FTP_FILE_ARRAY);
 
     }
 
     /**
      * Gets an array of at most {@code quantityRequested} FTPFile objects starting at this object's internal iterator's current position, and working back
      * toward the beginning.
      *
      * If fewer than {@code quantityRequested} such elements are available, the returned array will have a length equal to the number of entries at and after
      * the current position. If no such entries are found, this array will have a length of 0.
      *
      * After this method is called this object's internal iterator is moved back by a number of positions equal to the size of the array returned.
      *
      * @param quantityRequested the maximum number of entries we want to get.
      * @return an array of at most {@code quantityRequested} FTPFile objects starting at the current position of this iterator within its list and at least the
      *         number of elements which exist in the list at and after its current position. This array will be in the same order as the underlying list (not
      *         reversed).
      *         <p>
      *         <strong> NOTE:</strong> This array may contain null members if any of the individual file listings failed to parse. The caller should check each
      *         entry for null before referencing it.
      */
     public FTPFile[] getPrevious(final int quantityRequested) {
         final List<FTPFile> tmpResults = new LinkedList<>();
         int count = quantityRequested;
         while (count > 0 && internalIterator.hasPrevious()) {
             final String entry = internalIterator.previous();
             FTPFile temp = parser.parseFTPEntry(entry);
             if (temp == null && saveUnparseableEntries) {
                 temp = new FTPFile(entry);
             }
             tmpResults.add(0, temp);
             count--;
         }
         return tmpResults.toArray(EMPTY_FTP_FILE_ARRAY);
     }
 
     /**
      * convenience method to allow clients to know whether this object's internal iterator's current position is at the end of the list.
      *
      * @return true if internal iterator is not at end of list, false otherwise.
      */
     public boolean hasNext() {
         return internalIterator.hasNext();
     }
 
     /**
      * convenience method to allow clients to know whether this object's internal iterator's current position is at the beginning of the list.
      *
      * @return true if internal iterator is not at beginning of list, false otherwise.
      */
     public boolean hasPrevious() {
         return internalIterator.hasPrevious();
     }
 
     /**
      * Internal method for reading (and closing) the input into the {@code entries} list. After this method has completed, {@code entries} will contain a
      * collection of entries (as defined by {@code FTPFileEntryParser.readNextEntry()}), but this may contain various non-entry preliminary lines from the
      * server output, duplicates, and other data that will not be part of the final listing.
      *
      * @param inputStream The socket stream on which the input will be read.
      * @param charsetName The encoding to use.
      * @throws IOException thrown on any failure to read the stream
      */
     private void read(final InputStream inputStream, final String charsetName) throws IOException {
         try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, Charsets.toCharset(charsetName)))) {
             String line = parser.readNextEntry(reader);
             while (line != null) {
                 entries.add(line);
                 line = parser.readNextEntry(reader);
             }
         }
     }
 
     /**
      * Do not use.
      *
      * @param inputStream the stream from which to read
      * @throws IOException on error
      * @deprecated Use {@link #readServerList(InputStream, String)} instead
      */
     @Deprecated
     public void readServerList(final InputStream inputStream) throws IOException {
         readServerList(inputStream, null);
     }
 
     /**
      * Reads (and closes) the initial reading and preparsing of the list returned by the server. After this method has completed, this object will contain a
      * list of unparsed entries (Strings) each referring to a unique file on the server.
      *
      * @param inputStream input stream provided by the server socket.
      * @param charsetName the encoding to be used for reading the stream
      * @throws IOException thrown on any failure to read from the sever.
      */
     public void readServerList(final InputStream inputStream, final String charsetName) throws IOException {
         entries = new LinkedList<>();
         read(inputStream, charsetName);
         parser.preParse(entries);
         resetIterator();
     }
 
     /**
      * resets this object's internal iterator to the beginning of the list.
      */
     public void resetIterator() {
         internalIterator = entries.listIterator();
     }
 
 }