/*
 * 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.
 */
package org.apache.lucene.codecs.blocktree;


import java.io.IOException;
import java.util.Arrays;

import org.apache.lucene.codecs.BlockTermState;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexOptions;
import org.apache.lucene.store.ByteArrayDataInput;
import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.automaton.Transition;
import org.apache.lucene.util.fst.FST;

// TODO: can we share this with the frame in STE?
final class IntersectTermsEnumFrame {
  final int ord;
  long fp;
  long fpOrig;
  long fpEnd;
  long lastSubFP;

  // private static boolean DEBUG = IntersectTermsEnum.DEBUG;

  // State in automaton
  int state;

  // State just before the last label
  int lastState;

  int metaDataUpto;

  byte[] suffixBytes = new byte[128];
  final ByteArrayDataInput suffixesReader = new ByteArrayDataInput();

  byte[] suffixLengthBytes;
  final ByteArrayDataInput suffixLengthsReader;

  byte[] statBytes = new byte[64];
  int statsSingletonRunLength = 0;
  final ByteArrayDataInput statsReader = new ByteArrayDataInput();

  byte[] floorData = new byte[32];
  final ByteArrayDataInput floorDataReader = new ByteArrayDataInput();

  // Length of prefix shared by all terms in this block
  int prefix;

  // Number of entries (term or sub-block) in this block
  int entCount;

  // Which term we will next read
  int nextEnt;

  // True if this block is either not a floor block,
  // or, it's the last sub-block of a floor block
  boolean isLastInFloor;

  // True if all entries are terms
  boolean isLeafBlock;

  int numFollowFloorBlocks;
  int nextFloorLabel;
        
  final Transition transition = new Transition();
  int transitionIndex;
  int transitionCount;

  FST.Arc<BytesRef> arc;

  final BlockTermState termState;

  // metadata buffer
  byte[] bytes = new byte[32];

  final ByteArrayDataInput bytesReader = new ByteArrayDataInput();

  // Cumulative output so far
  BytesRef outputPrefix;

  int startBytePos;
  int suffix;

  private final IntersectTermsEnum ite;
  private final int version;

  public IntersectTermsEnumFrame(IntersectTermsEnum ite, int ord) throws IOException {
    this.ite = ite;
    this.ord = ord;
    this.termState = ite.fr.parent.postingsReader.newTermState();
    this.termState.totalTermFreq = -1;
    this.version = ite.fr.parent.version;
    if (version >= BlockTreeTermsReader.VERSION_COMPRESSED_SUFFIXES) {
      suffixLengthBytes = new byte[32];
      suffixLengthsReader = new ByteArrayDataInput();
    } else {
      suffixLengthBytes = null;
      suffixLengthsReader = suffixesReader;
    }
  }

  void loadNextFloorBlock() throws IOException {
    assert numFollowFloorBlocks > 0: "nextFloorLabel=" + nextFloorLabel;

    do {
      fp = fpOrig + (floorDataReader.readVLong() >>> 1);
      numFollowFloorBlocks--;
      if (numFollowFloorBlocks != 0) {
        nextFloorLabel = floorDataReader.readByte() & 0xff;
      } else {
        nextFloorLabel = 256;
      }
    } while (numFollowFloorBlocks != 0 && nextFloorLabel <= transition.min);

    load(null);
  }

  public void setState(int state) {
    this.state = state;
    transitionIndex = 0;
    transitionCount = ite.automaton.getNumTransitions(state);
    if (transitionCount != 0) {
      ite.automaton.initTransition(state, transition);
      ite.automaton.getNextTransition(transition);
    } else {

      // Must set min to -1 so the "label < min" check never falsely triggers:
      transition.min = -1;

      // Must set max to -1 so we immediately realize we need to step to the next transition and then pop this frame:
      transition.max = -1;
    }
  }

  void load(BytesRef frameIndexData) throws IOException {
    if (frameIndexData != null) {
      floorDataReader.reset(frameIndexData.bytes, frameIndexData.offset, frameIndexData.length);
      // Skip first long -- has redundant fp, hasTerms
      // flag, isFloor flag
      final long code = floorDataReader.readVLong();
      if ((code & BlockTreeTermsReader.OUTPUT_FLAG_IS_FLOOR) != 0) {
        // Floor frame
        numFollowFloorBlocks = floorDataReader.readVInt();
        nextFloorLabel = floorDataReader.readByte() & 0xff;

        // If current state is not accept, and has transitions, we must process
        // first block in case it has empty suffix:
        if (ite.runAutomaton.isAccept(state) == false && transitionCount != 0) {
          // Maybe skip floor blocks:
          assert transitionIndex == 0: "transitionIndex=" + transitionIndex;
          while (numFollowFloorBlocks != 0 && nextFloorLabel <= transition.min) {
            fp = fpOrig + (floorDataReader.readVLong() >>> 1);
            numFollowFloorBlocks--;
            if (numFollowFloorBlocks != 0) {
              nextFloorLabel = floorDataReader.readByte() & 0xff;
            } else {
              nextFloorLabel = 256;
            }
          }
        }
      }
    }

    ite.in.seek(fp);
    int code = ite.in.readVInt();
    entCount = code >>> 1;
    assert entCount > 0;
    isLastInFloor = (code & 1) != 0;

    // term suffixes:
    if (version >= BlockTreeTermsReader.VERSION_COMPRESSED_SUFFIXES) {
      final long codeL = ite.in.readVLong();
      isLeafBlock = (codeL & 0x04) != 0;
      final int numSuffixBytes = (int) (codeL >>> 3);
      if (suffixBytes.length < numSuffixBytes) {
        suffixBytes = new byte[ArrayUtil.oversize(numSuffixBytes, 1)];
      }
      final CompressionAlgorithm compressionAlg;
      try {
        compressionAlg = CompressionAlgorithm.byCode((int) codeL & 0x03);
      } catch (IllegalArgumentException e) {
        throw new CorruptIndexException(e.getMessage(), ite.in, e);
      }
      compressionAlg.read(ite.in, suffixBytes, numSuffixBytes);
      suffixesReader.reset(suffixBytes, 0, numSuffixBytes);

      int numSuffixLengthBytes = ite.in.readVInt();
      final boolean allEqual = (numSuffixLengthBytes & 0x01) != 0;
      numSuffixLengthBytes >>>= 1;
      if (suffixLengthBytes.length < numSuffixLengthBytes) {
        suffixLengthBytes = new byte[ArrayUtil.oversize(numSuffixLengthBytes, 1)];
      }
      if (allEqual) {
        Arrays.fill(suffixLengthBytes, 0, numSuffixLengthBytes, ite.in.readByte());
      } else {
        ite.in.readBytes(suffixLengthBytes, 0, numSuffixLengthBytes);
      }
      suffixLengthsReader.reset(suffixLengthBytes, 0, numSuffixLengthBytes);
    } else {
      code = ite.in.readVInt();
      isLeafBlock = (code & 1) != 0;
      int numBytes = code >>> 1;
      if (suffixBytes.length < numBytes) {
        suffixBytes = new byte[ArrayUtil.oversize(numBytes, 1)];
      }
      ite.in.readBytes(suffixBytes, 0, numBytes);
      suffixesReader.reset(suffixBytes, 0, numBytes);
    }

    // stats
    int numBytes = ite.in.readVInt();
    if (statBytes.length < numBytes) {
      statBytes = new byte[ArrayUtil.oversize(numBytes, 1)];
    }
    ite.in.readBytes(statBytes, 0, numBytes);
    statsReader.reset(statBytes, 0, numBytes);
    statsSingletonRunLength = 0;
    metaDataUpto = 0;

    termState.termBlockOrd = 0;
    nextEnt = 0;

    // metadata
    numBytes = ite.in.readVInt();
    if (bytes.length < numBytes) {
      bytes = new byte[ArrayUtil.oversize(numBytes, 1)];
    }
    ite.in.readBytes(bytes, 0, numBytes);
    bytesReader.reset(bytes, 0, numBytes);

    if (!isLastInFloor) {
      // Sub-blocks of a single floor block are always
      // written one after another -- tail recurse:
      fpEnd = ite.in.getFilePointer();
    }
  }

  // TODO: maybe add scanToLabel; should give perf boost

  // Decodes next entry; returns true if it's a sub-block
  public boolean next() {
    if (isLeafBlock) {
      nextLeaf();
      return false;
    } else {
      return nextNonLeaf();
    }
  }

  public void nextLeaf() {
    assert nextEnt != -1 && nextEnt < entCount: "nextEnt=" + nextEnt + " entCount=" + entCount + " fp=" + fp;
    nextEnt++;
    suffix = suffixLengthsReader.readVInt();
    startBytePos = suffixesReader.getPosition();
    suffixesReader.skipBytes(suffix);
  }

  public boolean nextNonLeaf() {
    assert nextEnt != -1 && nextEnt < entCount: "nextEnt=" + nextEnt + " entCount=" + entCount + " fp=" + fp;
    nextEnt++;
    final int code = suffixLengthsReader.readVInt();
    suffix = code >>> 1;
    startBytePos = suffixesReader.getPosition();
    suffixesReader.skipBytes(suffix);
    if ((code & 1) == 0) {
      // A normal term
      termState.termBlockOrd++;
      return false;
    } else {
      // A sub-block; make sub-FP absolute:
      lastSubFP = fp - suffixLengthsReader.readVLong();
      return true;
    }
  }

  public int getTermBlockOrd() {
    return isLeafBlock ? nextEnt : termState.termBlockOrd;
  }

  public void decodeMetaData() throws IOException {

    // lazily catch up on metadata decode:
    final int limit = getTermBlockOrd();
    boolean absolute = metaDataUpto == 0;
    assert limit > 0;

    // TODO: better API would be "jump straight to term=N"???
    while (metaDataUpto < limit) {

      // TODO: we could make "tiers" of metadata, ie,
      // decode docFreq/totalTF but don't decode postings
      // metadata; this way caller could get
      // docFreq/totalTF w/o paying decode cost for
      // postings

      // TODO: if docFreq were bulk decoded we could
      // just skipN here:

      // stats
      if (version >= BlockTreeTermsReader.VERSION_COMPRESSED_SUFFIXES) {
        if (statsSingletonRunLength > 0) {
          termState.docFreq = 1;
          termState.totalTermFreq = 1;
          statsSingletonRunLength--;
        } else {
          int token = statsReader.readVInt();
          if (version >= BlockTreeTermsReader.VERSION_COMPRESSED_SUFFIXES && (token & 1) == 1) {
            termState.docFreq = 1;
            termState.totalTermFreq = 1;
            statsSingletonRunLength = token >>> 1;
          } else {
            termState.docFreq = token >>> 1;
            if (ite.fr.fieldInfo.getIndexOptions() == IndexOptions.DOCS) {
              termState.totalTermFreq = termState.docFreq;
            } else {
              termState.totalTermFreq = termState.docFreq + statsReader.readVLong();
            }
          }
        }
      } else {
        termState.docFreq = statsReader.readVInt();
        //if (DEBUG) System.out.println("    dF=" + state.docFreq);
        if (ite.fr.fieldInfo.getIndexOptions() == IndexOptions.DOCS) {
          termState.totalTermFreq = termState.docFreq; // all postings have freq=1
        } else {
          termState.totalTermFreq = termState.docFreq + statsReader.readVLong();
          //if (DEBUG) System.out.println("    totTF=" + state.totalTermFreq);
        }
      }
      // metadata
      ite.fr.parent.postingsReader.decodeTerm(bytesReader, ite.fr.fieldInfo, termState, absolute);

      metaDataUpto++;
      absolute = false;
    }
    termState.termBlockOrd = metaDataUpto;
  }
}
