code: package zemberek.morphology.analysis;
  
  import com.google.common.collect.ArrayListMultimap;
  import com.google.common.collect.HashMultimap;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Maps;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import java.util.stream.Collectors;
  import zemberek.core.logging.Log;
  import zemberek.core.turkish.TurkishAlphabet;
  import zemberek.morphology.lexicon.DictionaryItem;
  import zemberek.morphology.lexicon.RootLexicon;
  import zemberek.morphology.morphotactics.StemTransition;
  import zemberek.morphology.morphotactics.TurkishMorphotactics;
  
  public class StemTransitionsMapBased extends StemTransitionsBase implements StemTransitions {
  
    private ArrayListMultimap<String, StemTransition> multiStems =
        ArrayListMultimap.create(1000, 2);
    private HashMultimap<String, String> asciiKeys = null;
  
    // contains a map that holds dictionary items that has
    // multiple or different than item.root stem surface forms.
    private ArrayListMultimap<DictionaryItem, StemTransition> differentStemItems =
        ArrayListMultimap.create(1000, 2);
  
    private Map<String, StemTransition> singleStems = Maps.newConcurrentMap();
  
    private ReadWriteLock lock = new ReentrantReadWriteLock();
  
    public StemTransitionsMapBased(RootLexicon lexicon, TurkishMorphotactics morphotactics) {
      this.lexicon = lexicon;
      this.morphotactics = morphotactics;
      lexicon.forEach(this::addDictionaryItem);
    }
  
    //TODO: this is kind of a hack. Because StemTransitions may be shared between
    // analyzer classes, this may be necessary when one of them happens to be ascii tolerant
    // and other is not.
    private void generateAsciiTolerantMap() {
      lock.writeLock().lock();
      asciiKeys = HashMultimap.create(1000, 2);
      try {
  
        // generate MultiMap for ascii tolerant keys
        for (String s : singleStems.keySet()) {
          String ascii = TurkishAlphabet.INSTANCE.toAscii(s);
  
          if (TurkishAlphabet.INSTANCE.containsAsciiRelated(s)) {
            asciiKeys.put(ascii, s);
          }
        }
        for (StemTransition st : multiStems.values()) {
          String s = st.surface;
          String ascii = TurkishAlphabet.INSTANCE.toAscii(s);
          if (TurkishAlphabet.INSTANCE.containsAsciiRelated(s)) {
            asciiKeys.put(ascii, s);
          }
        }
      } finally {
        lock.writeLock().unlock();
      }
    }
  
    public synchronized Set<StemTransition> getTransitions() {
      HashSet<StemTransition> result = new HashSet<>(singleStems.values());
      result.addAll(multiStems.values());
      return result;
    }
  
    public RootLexicon getLexicon() {
      return lexicon;
    }
  
    private synchronized void addStemTransition(StemTransition stemTransition) {
      final String surfaceForm = stemTransition.surface;
      if (multiStems.containsKey(surfaceForm)) {
        multiStems.put(surfaceForm, stemTransition);
      } else if (singleStems.containsKey(surfaceForm)) {
        multiStems.put(surfaceForm, singleStems.get(surfaceForm));
        singleStems.remove(surfaceForm);
        multiStems.put(surfaceForm, stemTransition);
      } else {
        singleStems.put(surfaceForm, stemTransition);
      }
    }
  
    private synchronized void removeStemNode(StemTransition stemTransition) {
      final String surfaceForm = stemTransition.surface;
      if (multiStems.containsKey(surfaceForm)) {
        multiStems.remove(surfaceForm, stemTransition);
      } else if (singleStems.containsKey(surfaceForm)
          && singleStems.get(surfaceForm).item.equals(stemTransition.item)) {
        singleStems.remove(surfaceForm);
      }
      if (!differentStemItems.containsEntry(stemTransition.item, stemTransition)) {
        differentStemItems.remove(stemTransition.item, stemTransition);
      }
    }
  
    private LinkedHashSet<StemTransition> getTransitionsAsciiTolerant(String stem) {
      lock.readLock().lock();
      try {
        // add actual
        LinkedHashSet<StemTransition> result = new LinkedHashSet<>();
        if (singleStems.containsKey(stem)) {
          result.add(singleStems.get(stem));
        } else if (multiStems.containsKey(stem)) {
          result.addAll(multiStems.get(stem));
        }
        Set<String> asciiStems = asciiKeys.get(TurkishAlphabet.INSTANCE.toAscii(stem));
        for (String st : asciiStems) {
          if (singleStems.containsKey(st)) {
            result.add(singleStems.get(st));
          } else if (multiStems.containsKey(st)) {
            result.addAll(multiStems.get(st));
          }
        }
        return result;
      } finally {
        lock.readLock().unlock();
      }
    }
  
    private List<StemTransition> getTransitions(String stem) {
      lock.readLock().lock();
      try {
        if (singleStems.containsKey(stem)) {
          return Lists.newArrayList(singleStems.get(stem));
        } else if (multiStems.containsKey(stem)) {
          return Lists.newArrayList(multiStems.get(stem));
        } else {
          return Collections.emptyList();
        }
      } finally {
        lock.readLock().unlock();
      }
    }
  
    public List<StemTransition> getPrefixMatches(String input, boolean asciiTolerant) {
      if (asciiKeys == null && asciiTolerant) {
        generateAsciiTolerantMap();
      }
      lock.readLock().lock();
      try {
        List<StemTransition> matches = Lists.newArrayListWithCapacity(3);
        for (int i = 1; i <= input.length(); i++) {
          String stem = input.substring(0, i);
          if (asciiTolerant) {
            matches.addAll(getTransitionsAsciiTolerant(stem));
          } else {
            matches.addAll(getTransitions(stem));
          }
        }
        return matches;
      } finally {
        lock.readLock().unlock();
      }
    }
  
    public List<StemTransition> getTransitions(DictionaryItem item) {
      lock.readLock().lock();
      try {
        if (differentStemItems.containsKey(item)) {
          return differentStemItems.get(item);
        } else {
  
          List<StemTransition> transitions = getTransitions(item.root);
          return transitions.stream().filter(s -> s.item.equals(item)).collect(Collectors.toList());
        }
      } finally {
        lock.readLock().unlock();
      }
    }
  
    public void addDictionaryItem(DictionaryItem item) {
      lock.writeLock().lock();
      try {
        List<StemTransition> transitions = generate(item);
        for (StemTransition transition : transitions) {
          addStemTransition(transition);
        }
        if (transitions.size() > 1 || (transitions.size() == 1 && !item.root
            .equals(transitions.get(0).surface))) {
          differentStemItems.putAll(item, transitions);
        }
      } catch (Exception e) {
        Log.warn("Cannot generate stem transition for %s with reason %s", item, e.getMessage());
      } finally {
        lock.writeLock().unlock();
      }
    }
  
    public void removeDictionaryItem(DictionaryItem item) {
      lock.writeLock().lock();
      try {
        List<StemTransition> transitions = generate(item);
        for (StemTransition transition : transitions) {
          removeStemNode(transition);
        }
        if (differentStemItems.containsKey(item)) {
          differentStemItems.removeAll(item);
        }
      } catch (Exception e) {
        Log.warn("Cannot remove %s ", item, e.getMessage());
      } finally {
        lock.writeLock().unlock();
      }
    }
  
  }
  
  