/*
 This software was produced for the U. S. Government
 under Contract No. W15P7T-11-C-F600, and is
 subject to the Rights in Noncommercial Computer Software
 and Noncommercial Computer Software Documentation
 Clause 252.227-7014 (JUN 1995)

 Copyright 2013 The MITRE Corporation. All Rights Reserved.

 Licensed 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.opensextant.solrtexttagger;

import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.IntsRef;

import java.io.IOException;
import java.util.Map;

/**
 * Cursor into the terms that advances by prefix.
 */
class TermPrefixCursor {

  //Note: this could be a lot more efficient if MemoryPostingsFormat supported ordinal lookup.
  // Maybe that could be added to Lucene.

  private static final byte SEPARATOR_CHAR = ' ';
  private static final IntsRef EMPTY_INTSREF = new IntsRef();

  private final TermsEnum termsEnum;
  private final Bits liveDocs;
  private final Map<BytesRef, IntsRef> docIdsCache;

  private BytesRef prefixBuf;//we append to this
  private BytesRefBuilder prefixBufBuilder = new BytesRefBuilder();
  private boolean prefixBufOnLoan;//if true, PB is loaned; needs to be copied
  private PostingsEnum postingsEnum;
  private IntsRef docIds;

  TermPrefixCursor(TermsEnum termsEnum, Bits liveDocs, Map<BytesRef, IntsRef> docIdsCache) {
    this.termsEnum = termsEnum;
    this.liveDocs = liveDocs;
    this.docIdsCache = docIdsCache;
  }

  /** Appends the separator char (if not the first) plus the given word to the prefix buffer,
   * then seeks to it. If the seek fails, false is returned and this cursor
   * can be re-used as if in a new state.  The {@code word} BytesRef is considered temporary,
   * and is not saved within this class. */
  boolean advance(BytesRef word) throws IOException {
    if (prefixBuf == null) { // first advance
      //set prefixBuf to word temporary. When advance() completes, we either null out or copy.
      prefixBuf = word;
      prefixBufOnLoan = true;
      if (seekPrefix()) {//... and we have to
        ensureBufIsACopy();
        return true;
      } else {
        prefixBuf = null;//just to be darned sure 'word' isn't referenced here
        return false;
      }

    } else { // subsequent advance
      //append to existing
      assert !prefixBufOnLoan;

      prefixBufBuilder.append(SEPARATOR_CHAR);
      prefixBufBuilder.append(word);
      prefixBuf = prefixBufBuilder.get();
      if (seekPrefix()) {
        return true;
      } else {
        prefixBuf = null;
        return false;
      }
    }
  }

  private void ensureBufIsACopy() {
    if (!prefixBufOnLoan)
      return;

    prefixBufBuilder.clear();
    prefixBufBuilder.copyBytes(prefixBuf);
    prefixBuf = prefixBufBuilder.get();
    prefixBufOnLoan = false;
  }

  /** Seeks to prefixBuf or the next term that is prefixed by prefixBuf plus the separator char.
   * Sets docIds. **/
  private boolean seekPrefix() throws IOException {
    TermsEnum.SeekStatus seekStatus = termsEnum.seekCeil(prefixBuf);

    docIds = null;//invalidate
    switch (seekStatus) {
      case END:
        return false;

      case FOUND:
        postingsEnum = termsEnum.postings(liveDocs, postingsEnum, PostingsEnum.NONE);
        docIds = postingsEnumToIntsRef(postingsEnum);
        if (docIds.length > 0) {
          return true;
        }

        //Pretend we didn't find it; go to next term
        docIds = null;
        if (termsEnum.next() == null) { // case END
          return false;
        }
        //fall through to NOT_FOUND

      case NOT_FOUND:
        //termsEnum must start with prefixBuf to continue
        BytesRef teTerm = termsEnum.term();

        if (teTerm.length > prefixBuf.length) {
          for (int i = 0; i < prefixBuf.length; i++) {
            if (prefixBuf.bytes[prefixBuf.offset + i] != teTerm.bytes[teTerm.offset + i])
              return false;
          }
          if (teTerm.bytes[teTerm.offset + prefixBuf.length] != SEPARATOR_CHAR)
            return false;
          return true;
        }
        return false;
    }
    throw new IllegalStateException(seekStatus.toString());
  }

  /** Returns an IntsRef either cached or reading postingsEnum. Not null.
   * @param postingsEnum*/
  private IntsRef postingsEnumToIntsRef(PostingsEnum postingsEnum) throws IOException {
    // (The cache can have empty IntsRefs)

    //lookup prefixBuf in a cache
    if (docIdsCache != null) {
      docIds = docIdsCache.get(prefixBuf);
      if (docIds != null) {
        return docIds;
      }
    }

    //read postingsEnum
    docIds = new IntsRef(termsEnum.docFreq());
    int docId;
    while ((docId = postingsEnum.nextDoc()) != PostingsEnum.NO_MORE_DOCS) {
      docIds.ints[docIds.length++] = docId;
    }
    if (docIds.length == 0)
      docIds = EMPTY_INTSREF;

    //cache
    if (docIdsCache != null) {
      ensureBufIsACopy();
      //clone is shallow; that's okay as the prefix isn't overwritten; it's just appended to
      docIdsCache.put(prefixBuf.clone(), docIds);
    }
    return docIds;
  }

  /** The docIds of the last call to advance, if it returned true. It might be null, but
   * its length won't be 0. Treat as immutable. */
  IntsRef getDocIds() {
    assert docIds == null || docIds.length != 0;
    return docIds;
  }
}

@@ -3835,26 +3835,16 @@
 ostings(
-liveDocs, 
 postings
@@ -3920,16 +3920,26 @@
 ingsEnum
+, liveDocs
 );%0A     
@@ -4955,16 +4955,31 @@
 ingsEnum
+, Bits liveDocs
 ) throws
@@ -5369,24 +5369,119 @@
 ORE_DOCS) %7B%0A
+      if (liveDocs != null && !liveDocs.get(postingsEnum.docID())) %7B%0A        continue;%0A      %7D%0A
       docIds

update cursor to use new deleted docs API (https://issues.apache.org/jira/browse/LUCENE-6553) and fix #43