package org.apache.lucene.index;

/**
 * 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
 *
 *     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.
 */

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;

import org.apache.lucene.analysis.WhitespaceAnalyzer;
import org.apache.lucene.index.IndexWriter; // javadoc
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.FixedBitSet;
import org.apache.lucene.util.ReaderUtil;
import org.apache.lucene.util.Version;

/**
 * This tool splits input index into multiple equal parts. The method employed
 * here uses {@link IndexWriter#addIndexes(IndexReader...)} where the input data
 * comes from the input index with artificially applied deletes to the document
 * id-s that fall outside the selected partition.
 * <p>Note 1: Deletes are only applied to a buffered list of deleted docs and
 * don't affect the source index - this tool works also with read-only indexes.
 * <p>Note 2: the disadvantage of this tool is that source index needs to be
 * read as many times as there are parts to be created, hence the name of this
 * tool.
 *
 * <p><b>NOTE</b>: this tool is unaware of documents added
 * atomically via {@link IndexWriter#addDocuments} or {@link
 * IndexWriter#updateDocuments}, which means it can easily
 * break up such document groups.
 */
public class MultiPassIndexSplitter {
  /**
   * Split source index into multiple parts.
   * @param input source index, can be read-only, can have deletions, can have
   * multiple segments (or multiple readers).
   * @param outputs list of directories where the output parts will be stored.
   * @param seq if true, then the source index will be split into equal
   * increasing ranges of document id-s. If false, source document id-s will be
   * assigned in a deterministic round-robin fashion to one of the output splits.
   * @throws IOException
   * @deprecated use {@link #split(Version, IndexReader, Directory[], boolean)} instead. 
   *             This method will be removed in Lucene 4.0. 
   */
  @Deprecated
  public void split(IndexReader input, Directory[] outputs, boolean seq) throws IOException {
    split(Version.LUCENE_CURRENT, input, outputs, seq);
  }
  
  /**
   * Split source index into multiple parts.
   * @param input source index, can be read-only, can have deletions, can have
   * multiple segments (or multiple readers).
   * @param outputs list of directories where the output parts will be stored.
   * @param seq if true, then the source index will be split into equal
   * increasing ranges of document id-s. If false, source document id-s will be
   * assigned in a deterministic round-robin fashion to one of the output splits.
   * @throws IOException
   */
  public void split(Version version, IndexReader input, Directory[] outputs, boolean seq) throws IOException {
    if (outputs == null || outputs.length < 2) {
      throw new IOException("Invalid number of outputs.");
    }
    if (input == null || input.numDocs() < 2) {
      throw new IOException("Not enough documents for splitting");
    }
    int numParts = outputs.length;
    // wrap a potentially read-only input
    // this way we don't have to preserve original deletions because neither
    // deleteDocument(int) or undeleteAll() is applied to the wrapped input index.
    input = new FakeDeleteIndexReader(input);
    int maxDoc = input.maxDoc();
    int partLen = maxDoc / numParts;
    for (int i = 0; i < numParts; i++) {
      input.undeleteAll();
      if (seq) { // sequential range
        int lo = partLen * i;
        int hi = lo + partLen;
        // below range
        for (int j = 0; j < lo; j++) {
          input.deleteDocument(j);
        }
        // above range - last part collects all id-s that remained due to
        // integer rounding errors
        if (i < numParts - 1) {
          for (int j = hi; j < maxDoc; j++) {
            input.deleteDocument(j);
          }
        }
      } else {
        // round-robin
        for (int j = 0; j < maxDoc; j++) {
          if ((j + numParts - i) % numParts != 0) {
            input.deleteDocument(j);
          }
        }
      }
      IndexWriter w = new IndexWriter(outputs[i], new IndexWriterConfig(
          version,
          new WhitespaceAnalyzer(Version.LUCENE_CURRENT))
          .setOpenMode(OpenMode.CREATE));
      System.err.println("Writing part " + (i + 1) + " ...");
      w.addIndexes(input);
      w.close();
    }
    System.err.println("Done.");
  }
  
  @SuppressWarnings("deprecation")
  public static void main(String[] args) throws Exception {
    if (args.length < 5) {
      System.err.println("Usage: MultiPassIndexSplitter -out <outputDir> -num <numParts> [-seq] <inputIndex1> [<inputIndex2 ...]");
      System.err.println("\tinputIndex\tpath to input index, multiple values are ok");
      System.err.println("\t-out ouputDir\tpath to output directory to contain partial indexes");
      System.err.println("\t-num numParts\tnumber of parts to produce");
      System.err.println("\t-seq\tsequential docid-range split (default is round-robin)");
      System.exit(-1);
    }
    ArrayList<IndexReader> indexes = new ArrayList<IndexReader>();
    String outDir = null;
    int numParts = -1;
    boolean seq = false;
    for (int i = 0; i < args.length; i++) {
      if (args[i].equals("-out")) {
        outDir = args[++i];
      } else if (args[i].equals("-num")) {
        numParts = Integer.parseInt(args[++i]);
      } else if (args[i].equals("-seq")) {
        seq = true;
      } else {
        File file = new File(args[i]);
        if (!file.exists() || !file.isDirectory()) {
          System.err.println("Invalid input path - skipping: " + file);
          continue;
        }
        Directory dir = FSDirectory.open(new File(args[i]));
        try {
          if (!IndexReader.indexExists(dir)) {
            System.err.println("Invalid input index - skipping: " + file);
            continue;
          }
        } catch (Exception e) {
          System.err.println("Invalid input index - skipping: " + file);
          continue;
        }
        indexes.add(IndexReader.open(dir, true));
      }
    }
    if (outDir == null) {
      throw new Exception("Required argument missing: -out outputDir");
    }
    if (numParts < 2) {
      throw new Exception("Invalid value of required argument: -num numParts");
    }
    if (indexes.size() == 0) {
      throw new Exception("No input indexes to process");
    }
    File out = new File(outDir);
    if (!out.mkdirs()) {
      throw new Exception("Can't create output directory: " + out);
    }
    Directory[] dirs = new Directory[numParts];
    for (int i = 0; i < numParts; i++) {
      dirs[i] = FSDirectory.open(new File(out, "part-" + i));
    }
    MultiPassIndexSplitter splitter = new MultiPassIndexSplitter();
    IndexReader input;
    if (indexes.size() == 1) {
      input = indexes.get(0);
    } else {
      input = new MultiReader(indexes.toArray(new IndexReader[indexes.size()]));
    }
    splitter.split(Version.LUCENE_CURRENT, input, dirs, seq);
  }
  
  /**
   * This class pretends that it can write deletions to the underlying index.
   * Instead, deletions are buffered in a bitset and overlaid with the original
   * list of deletions.
   */
  private static final class FakeDeleteIndexReader extends MultiReader {

    public FakeDeleteIndexReader(IndexReader reader) throws IOException {
      super(initSubReaders(reader));
    }
    
    private static IndexReader[] initSubReaders(IndexReader reader) throws IOException {
      final ArrayList<IndexReader> subs = new ArrayList<IndexReader>();
      new ReaderUtil.Gather(reader) {
        @Override
        protected void add(int base, IndexReader r) {
          subs.add(new FakeDeleteAtomicIndexReader(r));
        }
      }.run();
      return subs.toArray(new IndexReader[subs.size()]);
    }

  }
  
  private static final class FakeDeleteAtomicIndexReader extends FilterIndexReader {
    FixedBitSet dels;
    FixedBitSet oldDels;

    public FakeDeleteAtomicIndexReader(IndexReader in) {
      super(in);
      assert in.getSequentialSubReaders() == null;
      dels = new FixedBitSet(in.maxDoc());
      if (in.hasDeletions()) {
        oldDels = new FixedBitSet(in.maxDoc());
        for (int i = 0; i < in.maxDoc(); i++) {
          if (in.isDeleted(i)) oldDels.set(i);
        }
        dels.or(oldDels);
      }
    }

    @Override
    public int numDocs() {
      return in.maxDoc() - dels.cardinality();
    }

    /**
     * Just removes our overlaid deletions - does not undelete the original
     * deletions.
     */
    @Override
    protected void doUndeleteAll() throws CorruptIndexException, IOException {
      dels = new FixedBitSet(in.maxDoc());
      if (oldDels != null) {
        dels.or(oldDels);
      }
    }

    @Override
    protected void doDelete(int n) throws CorruptIndexException, IOException {
      dels.set(n);
    }

    @Override
    public boolean hasDeletions() {
      return in.maxDoc() != this.numDocs();
    }

    @Override
    public boolean isDeleted(int n) {
      return dels.get(n);
    }

    @Override
    public IndexReader[] getSequentialSubReaders() {
      return null;
    }

    @Override
    public TermPositions termPositions() throws IOException {
      return new FilterTermPositions(in.termPositions()) {

        @Override
        public boolean next() throws IOException {
          boolean res;
          while ((res = super.next())) {
            if (!dels.get(doc())) {
              break;
            }
          }
          return res;
        }        
      };
    }
  }
}
