package org.apache.blur.command;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.SortedSet;

import org.apache.blur.command.annotation.RequiredArgument;
import org.apache.blur.command.commandtype.ClusterServerReadCommandSingleTable;
import org.apache.blur.utils.BlurUtil;
import org.apache.lucene.index.AtomicReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.index.TermsEnum.SeekStatus;
import org.apache.lucene.util.BytesRef;

import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

/**
 * 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.
 */
public class TermsCommand extends ClusterServerReadCommandSingleTable<List<String>> {
  private static final String NAME = "terms";

  @RequiredArgument
  private short size = 10;

  @RequiredArgument
  private String fieldName;

  @RequiredArgument
  private String startWith = "";

  @Override
  public List<String> execute(IndexContext context) throws IOException {
    return terms(context.getIndexReader(), fieldName, startWith, size);
  }

  @Override
  public List<String> combine(CombiningContext context, Map<? extends Location<?>, List<String>> results)
      throws IOException, InterruptedException {
    SortedSet<String> terms = Sets.newTreeSet();
    for (List<String> t : results.values()) {
      terms.addAll(t);
    }
    return Lists.newArrayList(terms).subList(0, Math.min((int) size, terms.size()));
  }

  @Override
  public String getName() {
    return NAME;
  }

  private static List<String> terms(IndexReader reader, String fieldName, String startWith, short size)
      throws IOException {

    Term term = getTerm(fieldName, startWith);
    List<String> terms = new ArrayList<String>(size);
    AtomicReader areader = BlurUtil.getAtomicReader(reader);
    Terms termsAll = areader.terms(term.field());

    if (termsAll == null) {
      return terms;
    }

    TermsEnum termEnum = termsAll.iterator(null);

    SeekStatus status = termEnum.seekCeil(term.bytes());

    if (status == SeekStatus.END) {
      return terms;
    }

    BytesRef currentTermText = termEnum.term();
    do {
      terms.add(currentTermText.utf8ToString());
      if (terms.size() >= size) {
        return terms;
      }
    } while ((currentTermText = termEnum.next()) != null);
    return terms;
  }

  private static Term getTerm(String fieldName, String value) {
    if (fieldName == null) {
      throw new NullPointerException("fieldName cannot be null.");
    }
    return new Term(fieldName, value);
  }

  public short getSize() {
    return size;
  }

  public void setSize(short size) {
    this.size = size;
  }

  public String getFieldName() {
    return fieldName;
  }

  public void setFieldName(String fieldName) {
    this.fieldName = fieldName;
  }

  public String getStartWith() {
    return startWith;
  }

  public void setStartWith(String startWith) {
    this.startWith = startWith;
  }
}