/*
 * 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.search.vectorhighlight;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.FieldType;
import org.apache.lucene.document.TextField;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.StoredFieldVisitor;
import org.apache.lucene.search.highlight.DefaultEncoder;
import org.apache.lucene.search.highlight.Encoder;
import org.apache.lucene.search.vectorhighlight.FieldFragList.WeightedFragInfo;
import org.apache.lucene.search.vectorhighlight.FieldFragList.WeightedFragInfo.SubInfo;
import org.apache.lucene.search.vectorhighlight.FieldPhraseList.WeightedPhraseInfo.Toffs;

/**
 * Base FragmentsBuilder implementation that supports colored pre/post tags and multivalued fields.
 *
 * <p>Uses {@link BoundaryScanner} to determine fragments.
 */
public abstract class BaseFragmentsBuilder implements FragmentsBuilder {

  protected String[] preTags, postTags;
  public static final String[] COLORED_PRE_TAGS = {
    "<b style=\"background:yellow\">", "<b style=\"background:lawngreen\">",
        "<b style=\"background:aquamarine\">",
    "<b style=\"background:magenta\">", "<b style=\"background:palegreen\">",
        "<b style=\"background:coral\">",
    "<b style=\"background:wheat\">", "<b style=\"background:khaki\">",
        "<b style=\"background:lime\">",
    "<b style=\"background:deepskyblue\">", "<b style=\"background:deeppink\">",
        "<b style=\"background:salmon\">",
    "<b style=\"background:peachpuff\">", "<b style=\"background:violet\">",
        "<b style=\"background:mediumpurple\">",
    "<b style=\"background:palegoldenrod\">", "<b style=\"background:darkkhaki\">",
        "<b style=\"background:springgreen\">",
    "<b style=\"background:turquoise\">", "<b style=\"background:powderblue\">"
  };
  public static final String[] COLORED_POST_TAGS = {"</b>"};
  private char multiValuedSeparator = ' ';
  private final BoundaryScanner boundaryScanner;
  private boolean discreteMultiValueHighlighting = false;

  protected BaseFragmentsBuilder() {
    this(new String[] {"<b>"}, new String[] {"</b>"});
  }

  protected BaseFragmentsBuilder(String[] preTags, String[] postTags) {
    this(preTags, postTags, new SimpleBoundaryScanner());
  }

  protected BaseFragmentsBuilder(BoundaryScanner boundaryScanner) {
    this(new String[] {"<b>"}, new String[] {"</b>"}, boundaryScanner);
  }

  protected BaseFragmentsBuilder(
      String[] preTags, String[] postTags, BoundaryScanner boundaryScanner) {
    this.preTags = preTags;
    this.postTags = postTags;
    this.boundaryScanner = boundaryScanner;
  }

  static Object checkTagsArgument(Object tags) {
    if (tags instanceof String) {
      return tags;
    } else if (tags instanceof String[]) {
      return tags;
    }
    throw new IllegalArgumentException("type of preTags/postTags must be a String or String[]");
  }

  public abstract List<WeightedFragInfo> getWeightedFragInfoList(List<WeightedFragInfo> src);

  private static final Encoder NULL_ENCODER = new DefaultEncoder();

  @Override
  public String createFragment(
      IndexReader reader, int docId, String fieldName, FieldFragList fieldFragList)
      throws IOException {
    return createFragment(reader, docId, fieldName, fieldFragList, preTags, postTags, NULL_ENCODER);
  }

  @Override
  public String[] createFragments(
      IndexReader reader,
      int docId,
      String fieldName,
      FieldFragList fieldFragList,
      int maxNumFragments)
      throws IOException {
    return createFragments(
        reader, docId, fieldName, fieldFragList, maxNumFragments, preTags, postTags, NULL_ENCODER);
  }

  @Override
  public String createFragment(
      IndexReader reader,
      int docId,
      String fieldName,
      FieldFragList fieldFragList,
      String[] preTags,
      String[] postTags,
      Encoder encoder)
      throws IOException {
    String[] fragments =
        createFragments(reader, docId, fieldName, fieldFragList, 1, preTags, postTags, encoder);
    if (fragments == null || fragments.length == 0) return null;
    return fragments[0];
  }

  @Override
  public String[] createFragments(
      IndexReader reader,
      int docId,
      String fieldName,
      FieldFragList fieldFragList,
      int maxNumFragments,
      String[] preTags,
      String[] postTags,
      Encoder encoder)
      throws IOException {

    if (maxNumFragments < 0) {
      throw new IllegalArgumentException(
          "maxNumFragments(" + maxNumFragments + ") must be positive number.");
    }

    List<WeightedFragInfo> fragInfos = fieldFragList.getFragInfos();
    Field[] values = getFields(reader, docId, fieldName);
    if (values.length == 0) {
      return null;
    }

    if (discreteMultiValueHighlighting && values.length > 1) {
      fragInfos = discreteMultiValueHighlighting(fragInfos, values);
    }

    fragInfos = getWeightedFragInfoList(fragInfos);
    int limitFragments = maxNumFragments < fragInfos.size() ? maxNumFragments : fragInfos.size();
    List<String> fragments = new ArrayList<>(limitFragments);

    StringBuilder buffer = new StringBuilder();
    int[] nextValueIndex = {0};
    for (int n = 0; n < limitFragments; n++) {
      WeightedFragInfo fragInfo = fragInfos.get(n);
      fragments.add(
          makeFragment(buffer, nextValueIndex, values, fragInfo, preTags, postTags, encoder));
    }
    return fragments.toArray(String[]::new);
  }

  protected Field[] getFields(IndexReader reader, int docId, final String fieldName)
      throws IOException {
    // according to javadoc, doc.getFields(fieldName) cannot be used with lazy loaded field???
    final List<Field> fields = new ArrayList<>();
    reader
        .storedFields()
        .document(
            docId,
            new StoredFieldVisitor() {

              @Override
              public void stringField(FieldInfo fieldInfo, String value) {
                Objects.requireNonNull(value, "String value should not be null");
                FieldType ft = new FieldType(TextField.TYPE_STORED);
                ft.setStoreTermVectors(fieldInfo.hasTermVectors());
                fields.add(new Field(fieldInfo.name, value, ft));
              }

              @Override
              public Status needsField(FieldInfo fieldInfo) {
                return fieldInfo.name.equals(fieldName) ? Status.YES : Status.NO;
              }
            });
    return fields.toArray(Field[]::new);
  }

  protected String makeFragment(
      StringBuilder buffer,
      int[] index,
      Field[] values,
      WeightedFragInfo fragInfo,
      String[] preTags,
      String[] postTags,
      Encoder encoder) {
    StringBuilder fragment = new StringBuilder();
    final int s = fragInfo.getStartOffset();
    int[] modifiedStartOffset = {s};
    String src =
        getFragmentSourceMSO(
            buffer, index, values, s, fragInfo.getEndOffset(), modifiedStartOffset);
    int srcIndex = 0;
    for (SubInfo subInfo : fragInfo.getSubInfos()) {
      for (Toffs to : subInfo.termsOffsets()) {
        fragment
            .append(
                encoder.encodeText(
                    src.substring(srcIndex, to.getStartOffset() - modifiedStartOffset[0])))
            .append(getPreTag(preTags, subInfo.seqnum()))
            .append(
                encoder.encodeText(
                    src.substring(
                        to.getStartOffset() - modifiedStartOffset[0],
                        to.getEndOffset() - modifiedStartOffset[0])))
            .append(getPostTag(postTags, subInfo.seqnum()));
        srcIndex = to.getEndOffset() - modifiedStartOffset[0];
      }
    }
    fragment.append(encoder.encodeText(src.substring(srcIndex)));
    return fragment.toString();
  }

  protected String getFragmentSourceMSO(
      StringBuilder buffer,
      int[] index,
      Field[] values,
      int startOffset,
      int endOffset,
      int[] modifiedStartOffset) {
    while (buffer.length() < endOffset && index[0] < values.length) {
      buffer.append(values[index[0]++].stringValue());
      buffer.append(getMultiValuedSeparator());
    }
    int bufferLength = buffer.length();
    // we added the multi value char to the last buffer, ignore it
    if (values[index[0] - 1].fieldType().tokenized()) {
      bufferLength--;
    }
    int eo =
        bufferLength < endOffset ? bufferLength : boundaryScanner.findEndOffset(buffer, endOffset);
    modifiedStartOffset[0] = boundaryScanner.findStartOffset(buffer, startOffset);
    return buffer.substring(modifiedStartOffset[0], eo);
  }

  protected String getFragmentSource(
      StringBuilder buffer, int[] index, Field[] values, int startOffset, int endOffset) {
    while (buffer.length() < endOffset && index[0] < values.length) {
      buffer.append(values[index[0]].stringValue());
      buffer.append(multiValuedSeparator);
      index[0]++;
    }
    int eo = buffer.length() < endOffset ? buffer.length() : endOffset;
    return buffer.substring(startOffset, eo);
  }

  protected List<WeightedFragInfo> discreteMultiValueHighlighting(
      List<WeightedFragInfo> fragInfos, Field[] fields) {
    Map<String, List<WeightedFragInfo>> fieldNameToFragInfos = new HashMap<>();
    for (Field field : fields) {
      fieldNameToFragInfos.put(field.name(), new ArrayList<WeightedFragInfo>());
    }

    fragInfos:
    for (WeightedFragInfo fragInfo : fragInfos) {
      int fieldStart;
      int fieldEnd = 0;
      for (Field field : fields) {
        if (field.stringValue().isEmpty()) {
          fieldEnd++;
          continue;
        }
        fieldStart = fieldEnd;
        fieldEnd += field.stringValue().length() + 1; // + 1 for going to next field with same name.

        if (fragInfo.getStartOffset() >= fieldStart
            && fragInfo.getEndOffset() >= fieldStart
            && fragInfo.getStartOffset() <= fieldEnd
            && fragInfo.getEndOffset() <= fieldEnd) {
          fieldNameToFragInfos.get(field.name()).add(fragInfo);
          continue fragInfos;
        }

        if (fragInfo.getSubInfos().isEmpty()) {
          continue fragInfos;
        }

        Toffs firstToffs = fragInfo.getSubInfos().get(0).termsOffsets().get(0);
        if (fragInfo.getStartOffset() >= fieldEnd || firstToffs.getStartOffset() >= fieldEnd) {
          continue;
        }

        int fragStart = fieldStart;
        if (fragInfo.getStartOffset() > fieldStart && fragInfo.getStartOffset() < fieldEnd) {
          fragStart = fragInfo.getStartOffset();
        }

        int fragEnd = fieldEnd;
        if (fragInfo.getEndOffset() > fieldStart && fragInfo.getEndOffset() < fieldEnd) {
          fragEnd = fragInfo.getEndOffset();
        }

        List<SubInfo> subInfos = new ArrayList<>();
        Iterator<SubInfo> subInfoIterator = fragInfo.getSubInfos().iterator();
        //  The boost of the new info will be the sum of the boosts of its SubInfos
        float boost = 0.0f;
        while (subInfoIterator.hasNext()) {
          SubInfo subInfo = subInfoIterator.next();
          List<Toffs> toffsList = new ArrayList<>();
          Iterator<Toffs> toffsIterator = subInfo.termsOffsets().iterator();
          while (toffsIterator.hasNext()) {
            Toffs toffs = toffsIterator.next();
            if (toffs.getStartOffset() >= fieldEnd) {
              // We've gone past this value so its not worth iterating any more.
              break;
            }
            boolean startsAfterField = toffs.getStartOffset() >= fieldStart;
            boolean endsBeforeField = toffs.getEndOffset() < fieldEnd;
            if (startsAfterField && endsBeforeField) {
              // The Toff is entirely within this value.
              toffsList.add(toffs);
              toffsIterator.remove();
            } else if (startsAfterField) {
              /*
               * The Toffs starts within this value but ends after this value
               * so we clamp the returned Toffs to this value and leave the
               * Toffs in the iterator for the next value of this field.
               */
              toffsList.add(new Toffs(toffs.getStartOffset(), fieldEnd - 1));
            } else if (endsBeforeField) {
              /*
               * The Toffs starts before this value but ends in this value
               * which means we're really continuing from where we left off
               * above. Since we use the remainder of the offset we can remove
               * it from the iterator.
               */
              toffsList.add(new Toffs(fieldStart, toffs.getEndOffset()));
              toffsIterator.remove();
            } else {
              /*
               * The Toffs spans the whole value so we clamp on both sides.
               * This is basically a combination of both arms of the loop
               * above.
               */
              toffsList.add(new Toffs(fieldStart, fieldEnd - 1));
            }
          }
          if (!toffsList.isEmpty()) {
            subInfos.add(new SubInfo(subInfo.text(), toffsList, subInfo.seqnum(), subInfo.boost()));
            boost += subInfo.boost();
          }

          if (subInfo.termsOffsets().isEmpty()) {
            subInfoIterator.remove();
          }
        }
        WeightedFragInfo weightedFragInfo =
            new WeightedFragInfo(fragStart, fragEnd, subInfos, boost);
        fieldNameToFragInfos.get(field.name()).add(weightedFragInfo);
      }
    }

    List<WeightedFragInfo> result = new ArrayList<>();
    for (List<WeightedFragInfo> weightedFragInfos : fieldNameToFragInfos.values()) {
      result.addAll(weightedFragInfos);
    }
    result.sort((info1, info2) -> info1.getStartOffset() - info2.getStartOffset());

    return result;
  }

  public void setMultiValuedSeparator(char separator) {
    multiValuedSeparator = separator;
  }

  public char getMultiValuedSeparator() {
    return multiValuedSeparator;
  }

  public boolean isDiscreteMultiValueHighlighting() {
    return discreteMultiValueHighlighting;
  }

  public void setDiscreteMultiValueHighlighting(boolean discreteMultiValueHighlighting) {
    this.discreteMultiValueHighlighting = discreteMultiValueHighlighting;
  }

  protected String getPreTag(int num) {
    return getPreTag(preTags, num);
  }

  protected String getPostTag(int num) {
    return getPostTag(postTags, num);
  }

  protected String getPreTag(String[] preTags, int num) {
    int n = num % preTags.length;
    return preTags[n];
  }

  protected String getPostTag(String[] postTags, int num) {
    int n = num % postTags.length;
    return postTags[n];
  }
}
