/*
 * 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 opennlp.tools.tokenize;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;

import opennlp.tools.dictionary.Dictionary;
import opennlp.tools.ml.EventTrainer;
import opennlp.tools.ml.TrainerFactory;
import opennlp.tools.ml.model.Event;
import opennlp.tools.ml.model.MaxentModel;
import opennlp.tools.util.DownloadUtil;
import opennlp.tools.util.ObjectStream;
import opennlp.tools.util.Span;
import opennlp.tools.util.StringList;
import opennlp.tools.util.TrainingParameters;

/**
 * A {@link Tokenizer} for converting raw text into separated tokens. It uses
 * Maximum Entropy to make its decisions. The features are loosely
 * based off of Jeff Reynar's UPenn thesis "Topic Segmentation:
 * Algorithms and Applications.", which is available from his
 * homepage: <a href="http://www.cis.upenn.edu/~jcreynar">http://www.cis.upenn.edu/~jcreynar</a>.
 * <p>
 * This implementation needs a statistical model to tokenize a text which reproduces
 * the tokenization observed in the training data used to create the model.
 * The {@link TokenizerModel} class encapsulates that model and provides
 * methods to create it from the binary representation.
 * <p>
 * A tokenizer instance is not thread-safe. For each thread, one tokenizer
 * must be instantiated which can share one {@link TokenizerModel} instance
 * to safe memory.
 * <p>
 * To train a new model, the {@link #train(ObjectStream, TokenizerFactory, TrainingParameters)} method
 * can be used.
 * <p>
 * Sample usage:
 * <p>
 * <code>
 * InputStream modelIn;<br>
 * <br>
 * ...<br>
 * <br>
 * TokenizerModel model = TokenizerModel(modelIn);<br>
 * <br>
 * Tokenizer tokenizer = new TokenizerME(model);<br>
 * <br>
 * String tokens[] = tokenizer.tokenize("A sentence to be tokenized.");
 * </code>
 * @see Tokenizer
 * @see TokenizerModel
 * @see TokenSample
 */
public class TokenizerME extends AbstractTokenizer {

  /**
   * Constant indicates a token split.
   */
  public static final String SPLIT = "T";

  /**
   * Constant indicates no token split.
   */
  public static final String NO_SPLIT = "F";

  private final Pattern alphanumeric;

  /*
   * The maximum entropy model to use to evaluate contexts.
   */
  private final MaxentModel model;

  /*
   * The context generator.
   */
  private final TokenContextGenerator cg;

  /*
   * Optimization flag to skip alphanumeric tokens for further tokenization
   */
  private final boolean useAlphaNumericOptimization;

  /*
   * List of probabilities for each token returned from a call to
   * <code>tokenize</code> or <code>tokenizePos</code>.
   */
  private final List<Double> tokProbs;

  private final List<Span> newTokens;

  /*
   * The {@link Dictionary abbreviation dictionary} if available (may be {@code null}).
   */
  private final Dictionary abbDict;

  /**
   * Initializes a {@link TokenizerME} by downloading a default model.
   * @param language The language of the tokenizer.
   * @throws IOException Thrown if the model cannot be downloaded or saved.
   */
  public TokenizerME(String language) throws IOException {
    this(DownloadUtil.downloadModel(language, DownloadUtil.ModelType.TOKENIZER,
            TokenizerModel.class));
  }

  /**
   * Instantiates a {@link TokenizerME} with an existing {@link TokenizerModel}.
   *
   * @param model The {@link TokenizerModel} to be used.
   */
  public TokenizerME(TokenizerModel model) {
    TokenizerFactory factory = model.getFactory();
    this.alphanumeric = factory.getAlphaNumericPattern();
    this.cg = factory.getContextGenerator();
    this.model = model.getMaxentModel();
    this.useAlphaNumericOptimization = factory.isUseAlphaNumericOptimization();

    abbDict = model.getAbbreviations();
    newTokens = new ArrayList<>();
    tokProbs = new ArrayList<>(50);
  }

  /**
   * @return the probabilities associated with the most recent calls to
   *         {@link TokenizerME#tokenize(String)} or {@link TokenizerME#tokenizePos(String)}.
   *         If not applicable an empty array is returned.
   */
  public double[] getTokenProbabilities() {
    double[] tokProbArray = new double[tokProbs.size()];
    for (int i = 0; i < tokProbArray.length; i++) {
      tokProbArray[i] = tokProbs.get(i);
    }
    return tokProbArray;
  }

  /**
   * Tokenizes the string.
   *
   * @param d  The string to be tokenized.
   *
   * @return   A {@link Span} array containing individual tokens as elements.
   */
  @Override
  public Span[] tokenizePos(String d) {
    WhitespaceTokenizer whitespaceTokenizer = WhitespaceTokenizer.INSTANCE;
    whitespaceTokenizer.setKeepNewLines(keepNewLines);
    Span[] tokens = whitespaceTokenizer.tokenizePos(d);
    newTokens.clear();
    tokProbs.clear();
    for (Span s : tokens) {
      String tok = d.substring(s.getStart(), s.getEnd());
      // Can't tokenize single characters
      if (tok.length() < 2) {
        newTokens.add(s);
        tokProbs.add(1d);
      } else if (useAlphaNumericOptimization() && alphanumeric.matcher(tok).matches()) {
        newTokens.add(s);
        tokProbs.add(1d);
      } else {
        int start = s.getStart();
        int end = s.getEnd();
        final int origStart = s.getStart();
        double tokenProb = 1.0;
        for (int j = origStart + 1; j < end; j++) {
          double[] probs =
              model.eval(cg.getContext(tok, j - origStart));
          String best = model.getBestOutcome(probs);
          tokenProb *= probs[model.getIndex(best)];
          if (best.equals(TokenizerME.SPLIT)) {
            if (isAcceptableAbbreviation(tok)) {
              newTokens.add(new Span(start, end));
              tokProbs.add(tokenProb);
              long numberOfDots = tok.codePoints().filter(ch -> ch == '.').count();
              j = j + (int) numberOfDots; // To compensate for abbreviation dot(s)
              start = j + 1;
            } else {
              newTokens.add(new Span(start, j));
              tokProbs.add(tokenProb);
              start = j;
            }
            tokenProb = 1.0;
          }
        }
        if (start < end) {
          newTokens.add(new Span(start, end));
          tokProbs.add(tokenProb);
        }
      }
    }

    Span[] spans = new Span[newTokens.size()];
    newTokens.toArray(spans);
    return spans;
  }

  /**
   * Trains a model for the {@link TokenizerME}.
   *
   * @param samples The samples used for the training.
   * @param factory A {@link TokenizerFactory} to get resources from.
   * @param mlParams The machine learning {@link TrainingParameters train parameters}.
   * @return A trained {@link TokenizerModel}.
   * @throws IOException Thrown during IO operations on a temp file which is created
   *           during training. Or if reading from the {@link ObjectStream} fails.
   */
  public static TokenizerModel train(ObjectStream<TokenSample> samples, TokenizerFactory factory,
      TrainingParameters mlParams) throws IOException {

    Map<String, String> manifestInfoEntries = new HashMap<>();

    ObjectStream<Event> eventStream = new TokSpanEventStream(samples,
        factory.isUseAlphaNumericOptimization(),
        factory.getAlphaNumericPattern(), factory.getContextGenerator());

    EventTrainer trainer = TrainerFactory.getEventTrainer(
        mlParams, manifestInfoEntries);

    MaxentModel maxentModel = trainer.train(eventStream);

    return new TokenizerModel(maxentModel, manifestInfoEntries, factory);
  }

  /**
   * @return {@code true} if the tokenizer uses alphanumeric optimization, {@code false} otherwise.
   */
  public boolean useAlphaNumericOptimization() {
    return useAlphaNumericOptimization;
  }

  /**
   * Allows checking a token abbreviation candidate for acceptability.
   *
   * <p>Note: The implementation always returns {@code false} if no
   * abbreviation dictionary is available for the underlying model.</p>
   *
   * @param s the {@link CharSequence token} to check for.
   * @return {@code true} if the candidate is acceptable, {@code false} otherwise.
   */
  protected boolean isAcceptableAbbreviation(CharSequence s) {
    if (abbDict == null)
      return false;

    return abbDict.contains(new StringList(s.toString()));
  }
}
