package org.apache.lucene.analysis.hunspell;

/*
 * 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.
 */

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

import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.store.ByteArrayDataInput;
import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.CharsRef;
import org.apache.lucene.util.IntsRef;
import org.apache.lucene.util.automaton.CharacterRunAutomaton;
import org.apache.lucene.util.fst.FST;
import org.apache.lucene.util.fst.Outputs;

/**
 * Stemmer uses the affix rules declared in the Dictionary to generate one or more stems for a word.  It
 * conforms to the algorithm in the original hunspell algorithm, including recursive suffix stripping.
 */
final class Stemmer {
  private final Dictionary dictionary;
  private final BytesRef scratch = new BytesRef();
  private final StringBuilder segment = new StringBuilder();
  private final ByteArrayDataInput affixReader;
  
  // used for normalization
  private final StringBuilder scratchSegment = new StringBuilder();
  private char scratchBuffer[] = new char[32];
  
  // its '1' if we have no stem exceptions, otherwise every other form
  // is really an ID pointing to the exception table
  private final int formStep;
  
  /**
   * Constructs a new Stemmer which will use the provided Dictionary to create its stems.
   *
   * @param dictionary Dictionary that will be used to create the stems
   */
  public Stemmer(Dictionary dictionary) {
    this.dictionary = dictionary;
    this.affixReader = new ByteArrayDataInput(dictionary.affixData);
    for (int level = 0; level < 3; level++) {
      if (dictionary.prefixes != null) {
        prefixArcs[level] = new FST.Arc<>();
        prefixReaders[level] = dictionary.prefixes.getBytesReader();
      }
      if (dictionary.suffixes != null) {
        suffixArcs[level] = new FST.Arc<>();
        suffixReaders[level] = dictionary.suffixes.getBytesReader();
      }
    }
    formStep = dictionary.hasStemExceptions ? 2 : 1;
  } 
  
  /**
   * Find the stem(s) of the provided word.
   * 
   * @param word Word to find the stems for
   * @return List of stems for the word
   */
  public List<CharsRef> stem(String word) {
    return stem(word.toCharArray(), word.length());
  }

  /**
   * Find the stem(s) of the provided word
   * 
   * @param word Word to find the stems for
   * @return List of stems for the word
   */
  public List<CharsRef> stem(char word[], int length) {    

    if (dictionary.needsInputCleaning) {
      scratchSegment.setLength(0);
      scratchSegment.append(word, 0, length);
      CharSequence cleaned = dictionary.cleanInput(scratchSegment, segment);
      scratchBuffer = ArrayUtil.grow(scratchBuffer, cleaned.length());
      length = segment.length();
      segment.getChars(0, length, scratchBuffer, 0);
      word = scratchBuffer;
    }
    
    int caseType = caseOf(word, length);
    if (caseType == UPPER_CASE) {
      // upper: union exact, title, lower
      caseFoldTitle(word, length);
      caseFoldLower(titleBuffer, length);
      List<CharsRef> list = doStem(word, length, false);
      list.addAll(doStem(titleBuffer, length, true));
      list.addAll(doStem(lowerBuffer, length, true));
      return list;
    } else if (caseType == TITLE_CASE) {
      // title: union exact, lower
      caseFoldLower(word, length);
      List<CharsRef> list = doStem(word, length, false);
      list.addAll(doStem(lowerBuffer, length, true));
      return list;
    } else {
      // exact match only
      return doStem(word, length, false);
    }
  }
  
  // temporary buffers for case variants
  private char[] lowerBuffer = new char[8];
  private char[] titleBuffer = new char[8];
  
  private static final int EXACT_CASE = 0;
  private static final int TITLE_CASE = 1;
  private static final int UPPER_CASE = 2;
  
  /** returns EXACT_CASE,TITLE_CASE, or UPPER_CASE type for the word */
  private int caseOf(char word[], int length) {
    if (dictionary.ignoreCase || length == 0 || !Character.isUpperCase(word[0])) {
      return EXACT_CASE;
    }
    
    // determine if we are title or lowercase (or something funky, in which its exact)
    boolean seenUpper = false;
    boolean seenLower = false;
    for (int i = 1; i < length; i++) {
      boolean v = Character.isUpperCase(word[i]);
      seenUpper |= v;
      seenLower |= !v;
    }
    
    if (!seenLower) {
      return UPPER_CASE;
    } else if (!seenUpper) {
      return TITLE_CASE;
    } else {
      return EXACT_CASE;
    }
  }
  
  /** folds titlecase variant of word to titleBuffer */
  private void caseFoldTitle(char word[], int length) {
    titleBuffer = ArrayUtil.grow(titleBuffer, length);
    System.arraycopy(word, 0, titleBuffer, 0, length);
    for (int i = 1; i < length; i++) {
      titleBuffer[i] = dictionary.caseFold(titleBuffer[i]);
    }
  }
  
  /** folds lowercase variant of word (title cased) to lowerBuffer */
  private void caseFoldLower(char word[], int length) {
    lowerBuffer = ArrayUtil.grow(lowerBuffer, length);
    System.arraycopy(word, 0, lowerBuffer, 0, length);
    lowerBuffer[0] = dictionary.caseFold(lowerBuffer[0]);
  }
  
  private List<CharsRef> doStem(char word[], int length, boolean caseVariant) {
    List<CharsRef> stems = new ArrayList<>();
    IntsRef forms = dictionary.lookupWord(word, 0, length);
    if (forms != null) {
      for (int i = 0; i < forms.length; i += formStep) {
        boolean checkKeepCase = caseVariant && dictionary.keepcase != -1;
        boolean checkNeedAffix = dictionary.needaffix != -1;
        boolean checkOnlyInCompound = dictionary.onlyincompound != -1;
        if (checkKeepCase || checkNeedAffix || checkOnlyInCompound) {
          dictionary.flagLookup.get(forms.ints[forms.offset+i], scratch);
          char wordFlags[] = Dictionary.decodeFlags(scratch);
          // we are looking for a case variant, but this word does not allow it
          if (checkKeepCase && Dictionary.hasFlag(wordFlags, (char)dictionary.keepcase)) {
            continue;
          }
          // we can't add this form, its a pseudostem requiring an affix
          if (checkNeedAffix && Dictionary.hasFlag(wordFlags, (char)dictionary.needaffix)) {
            continue;
          }
          // we can't add this form, it only belongs inside a compound word
          if (checkOnlyInCompound && Dictionary.hasFlag(wordFlags, (char)dictionary.onlyincompound)) {
            continue;
          }
        }
        stems.add(newStem(word, length, forms, i));
      }
    }
    try {
      boolean v = stems.addAll(stem(word, length, -1, -1, -1, 0, true, true, false, false, caseVariant));
    } catch (IOException bogus) {
      throw new RuntimeException(bogus);
    }
    return stems;
  }
  
  /**
   * Find the unique stem(s) of the provided word
   * 
   * @param word Word to find the stems for
   * @return List of stems for the word
   */
  public List<CharsRef> uniqueStems(char word[], int length) {
    List<CharsRef> stems = stem(word, length);
    if (stems.size() < 2) {
      return stems;
    }
    CharArraySet terms = new CharArraySet(8, dictionary.ignoreCase);
    List<CharsRef> deduped = new ArrayList<>();
    for (CharsRef s : stems) {
      if (!terms.contains(s)) {
        deduped.add(s);
        terms.add(s);
      }
    }
    return deduped;
  }
  
  private CharsRef newStem(char buffer[], int length, IntsRef forms, int formID) {
    final String exception;
    if (dictionary.hasStemExceptions) {
      int exceptionID = forms.ints[forms.offset + formID + 1];
      if (exceptionID > 0) {
        exception = dictionary.getStemException(exceptionID);
      } else {
        exception = null;
      }
    } else {
      exception = null;
    }
    
    if (dictionary.needsOutputCleaning) {
      scratchSegment.setLength(0);
      if (exception != null) {
        scratchSegment.append(exception);
      } else {
        scratchSegment.append(buffer, 0, length);
      }
      try {
        Dictionary.applyMappings(dictionary.oconv, scratchSegment);
      } catch (IOException bogus) {
        throw new RuntimeException(bogus);
      }
      char cleaned[] = new char[scratchSegment.length()];
      scratchSegment.getChars(0, cleaned.length, cleaned, 0);
      return new CharsRef(cleaned, 0, cleaned.length);
    } else {
      if (exception != null) {
        return new CharsRef(exception);
      } else {
        return new CharsRef(buffer, 0, length);
      }
    }
  }

  // ================================================= Helper Methods ================================================

  // some state for traversing FSTs
  final FST.BytesReader prefixReaders[] = new FST.BytesReader[3];
  @SuppressWarnings("unchecked")
  final FST.Arc<IntsRef> prefixArcs[] = new FST.Arc[3];
  
  final FST.BytesReader suffixReaders[] = new FST.BytesReader[3];
  @SuppressWarnings("unchecked")
  final FST.Arc<IntsRef> suffixArcs[] = new FST.Arc[3];

  
  /**
   * Generates a list of stems for the provided word
   *
   * @param word Word to generate the stems for
   * @param previous previous affix that was removed (so we dont remove same one twice)
   * @param prevFlag Flag from a previous stemming step that need to be cross-checked with any affixes in this recursive step
   * @param prefixFlag flag of the most inner removed prefix, so that when removing a suffix, its also checked against the word
   * @param recursionDepth current recursiondepth
   * @param doPrefix true if we should remove prefixes
   * @param doSuffix true if we should remove suffixes
   * @param previousWasPrefix true if the previous removal was a prefix:
   *        if we are removing a suffix, and it has no continuation requirements, its ok.
   *        but two prefixes (COMPLEXPREFIXES) or two suffixes must have continuation requirements to recurse. 
   * @param circumfix true if the previous prefix removal was signed as a circumfix
   *        this means inner most suffix must also contain circumfix flag.
   * @param caseVariant true if we are searching for a case variant. if the word has KEEPCASE flag it cannot succeed.
   * @return List of stems, or empty list if no stems are found
   */
  private List<CharsRef> stem(char word[], int length, int previous, int prevFlag, int prefixFlag, int recursionDepth, boolean doPrefix, boolean doSuffix, boolean previousWasPrefix, boolean circumfix, boolean caseVariant) throws IOException {
    
    // TODO: allow this stuff to be reused by tokenfilter
    List<CharsRef> stems = new ArrayList<>();
    
    if (doPrefix && dictionary.prefixes != null) {
      FST<IntsRef> fst = dictionary.prefixes;
      Outputs<IntsRef> outputs = fst.outputs;
      FST.BytesReader bytesReader = prefixReaders[recursionDepth];
      FST.Arc<IntsRef> arc = prefixArcs[recursionDepth];
      fst.getFirstArc(arc);
      IntsRef NO_OUTPUT = outputs.getNoOutput();
      IntsRef output = NO_OUTPUT;
      int limit = dictionary.fullStrip ? length : length-1;
      for (int i = 0; i < limit; i++) {
        if (i > 0) {
          int ch = word[i-1];
          if (fst.findTargetArc(ch, arc, arc, bytesReader) == null) {
            break;
          } else if (arc.output != NO_OUTPUT) {
            output = fst.outputs.add(output, arc.output);
          }
        }
        IntsRef prefixes = null;
        if (!arc.isFinal()) {
          continue;
        } else {
          prefixes = fst.outputs.add(output, arc.nextFinalOutput);
        }
        
        for (int j = 0; j < prefixes.length; j++) {
          int prefix = prefixes.ints[prefixes.offset + j];
          if (prefix == previous) {
            continue;
          }
          affixReader.setPosition(8 * prefix);
          char flag = (char) (affixReader.readShort() & 0xffff);
          char stripOrd = (char) (affixReader.readShort() & 0xffff);
          int condition = (char) (affixReader.readShort() & 0xffff);
          boolean crossProduct = (condition & 1) == 1;
          condition >>>= 1;
          char append = (char) (affixReader.readShort() & 0xffff);
          
          final boolean compatible;
          if (recursionDepth == 0) {
            if (dictionary.onlyincompound == -1) {
              compatible = true;
            } else {
              // check if affix is allowed in a non-compound word
              dictionary.flagLookup.get(append, scratch);
              char appendFlags[] = Dictionary.decodeFlags(scratch);
              compatible = !Dictionary.hasFlag(appendFlags, (char) dictionary.onlyincompound);
            }
          } else if (crossProduct) {
            // cross check incoming continuation class (flag of previous affix) against list.
            dictionary.flagLookup.get(append, scratch);
            char appendFlags[] = Dictionary.decodeFlags(scratch);
            assert prevFlag >= 0;
            boolean allowed = dictionary.onlyincompound == -1 || 
                              !Dictionary.hasFlag(appendFlags, (char) dictionary.onlyincompound);
            compatible = allowed && hasCrossCheckedFlag((char)prevFlag, appendFlags, false);
          } else {
            compatible = false;
          }
          
          if (compatible) {
            int deAffixedStart = i;
            int deAffixedLength = length - deAffixedStart;
            
            int stripStart = dictionary.stripOffsets[stripOrd];
            int stripEnd = dictionary.stripOffsets[stripOrd+1];
            int stripLength = stripEnd - stripStart;
            
            if (!checkCondition(condition, dictionary.stripData, stripStart, stripLength, word, deAffixedStart, deAffixedLength)) {
              continue;
            }
            
            char strippedWord[] = new char[stripLength + deAffixedLength];
            System.arraycopy(dictionary.stripData, stripStart, strippedWord, 0, stripLength);
            System.arraycopy(word, deAffixedStart, strippedWord, stripLength, deAffixedLength);

            List<CharsRef> stemList = applyAffix(strippedWord, strippedWord.length, prefix, -1, recursionDepth, true, circumfix, caseVariant);
            
            stems.addAll(stemList);
          }
        }
      }
    } 
    
    if (doSuffix && dictionary.suffixes != null) {
      FST<IntsRef> fst = dictionary.suffixes;
      Outputs<IntsRef> outputs = fst.outputs;
      FST.BytesReader bytesReader = suffixReaders[recursionDepth];
      FST.Arc<IntsRef> arc = suffixArcs[recursionDepth];
      fst.getFirstArc(arc);
      IntsRef NO_OUTPUT = outputs.getNoOutput();
      IntsRef output = NO_OUTPUT;
      int limit = dictionary.fullStrip ? 0 : 1;
      for (int i = length; i >= limit; i--) {
        if (i < length) {
          int ch = word[i];
          if (fst.findTargetArc(ch, arc, arc, bytesReader) == null) {
            break;
          } else if (arc.output != NO_OUTPUT) {
            output = fst.outputs.add(output, arc.output);
          }
        }
        IntsRef suffixes = null;
        if (!arc.isFinal()) {
          continue;
        } else {
          suffixes = fst.outputs.add(output, arc.nextFinalOutput);
        }
        
        for (int j = 0; j < suffixes.length; j++) {
          int suffix = suffixes.ints[suffixes.offset + j];
          if (suffix == previous) {
            continue;
          }
          affixReader.setPosition(8 * suffix);
          char flag = (char) (affixReader.readShort() & 0xffff);
          char stripOrd = (char) (affixReader.readShort() & 0xffff);
          int condition = (char) (affixReader.readShort() & 0xffff);
          boolean crossProduct = (condition & 1) == 1;
          condition >>>= 1;
          char append = (char) (affixReader.readShort() & 0xffff);
          
          final boolean compatible;
          if (recursionDepth == 0) {
            if (dictionary.onlyincompound == -1) {
              compatible = true;
            } else {
              // check if affix is allowed in a non-compound word
              dictionary.flagLookup.get(append, scratch);
              char appendFlags[] = Dictionary.decodeFlags(scratch);
              compatible = !Dictionary.hasFlag(appendFlags, (char) dictionary.onlyincompound);
            }
          } else if (crossProduct) {
            // cross check incoming continuation class (flag of previous affix) against list.
            dictionary.flagLookup.get(append, scratch);
            char appendFlags[] = Dictionary.decodeFlags(scratch);
            assert prevFlag >= 0;
            boolean allowed = dictionary.onlyincompound == -1 || 
                              !Dictionary.hasFlag(appendFlags, (char) dictionary.onlyincompound);
            compatible = allowed && hasCrossCheckedFlag((char)prevFlag, appendFlags, previousWasPrefix);
          } else {
            compatible = false;
          }
          
          if (compatible) {
            int appendLength = length - i;
            int deAffixedLength = length - appendLength;
            
            int stripStart = dictionary.stripOffsets[stripOrd];
            int stripEnd = dictionary.stripOffsets[stripOrd+1];
            int stripLength = stripEnd - stripStart;
            
            if (!checkCondition(condition, word, 0, deAffixedLength, dictionary.stripData, stripStart, stripLength)) {
              continue;
            }

            char strippedWord[] = new char[stripLength + deAffixedLength];
            System.arraycopy(word, 0, strippedWord, 0, deAffixedLength);
            System.arraycopy(dictionary.stripData, stripStart, strippedWord, deAffixedLength, stripLength);
            
            List<CharsRef> stemList = applyAffix(strippedWord, strippedWord.length, suffix, prefixFlag, recursionDepth, false, circumfix, caseVariant);
            
            stems.addAll(stemList);
          }
        }
      }
    }

    return stems;
  }
  
  /** checks condition of the concatenation of two strings */
  // note: this is pretty stupid, we really should subtract strip from the condition up front and just check the stem
  // but this is a little bit more complicated.
  private boolean checkCondition(int condition, char c1[], int c1off, int c1len, char c2[], int c2off, int c2len) {
    if (condition != 0) {
      CharacterRunAutomaton pattern = dictionary.patterns.get(condition);
      int state = pattern.getInitialState();
      for (int i = c1off; i < c1off + c1len; i++) {
        state = pattern.step(state, c1[i]);
        if (state == -1) {
          return false;
        }
      }
      for (int i = c2off; i < c2off + c2len; i++) {
        state = pattern.step(state, c2[i]);
        if (state == -1) {
          return false;
        }
      }
      return pattern.isAccept(state);
    }
    return true;
  }

  /**
   * Applies the affix rule to the given word, producing a list of stems if any are found
   *
   * @param strippedWord Word the affix has been removed and the strip added
   * @param length valid length of stripped word
   * @param affix HunspellAffix representing the affix rule itself
   * @param prefixFlag when we already stripped a prefix, we cant simply recurse and check the suffix, unless both are compatible
   *                   so we must check dictionary form against both to add it as a stem!
   * @param recursionDepth current recursion depth
   * @param prefix true if we are removing a prefix (false if its a suffix)
   * @return List of stems for the word, or an empty list if none are found
   */
  List<CharsRef> applyAffix(char strippedWord[], int length, int affix, int prefixFlag, int recursionDepth, boolean prefix, boolean circumfix, boolean caseVariant) throws IOException {    
    // TODO: just pass this in from before, no need to decode it twice
    affixReader.setPosition(8 * affix);
    char flag = (char) (affixReader.readShort() & 0xffff);
    affixReader.skipBytes(2); // strip
    int condition = (char) (affixReader.readShort() & 0xffff);
    boolean crossProduct = (condition & 1) == 1;
    condition >>>= 1;
    char append = (char) (affixReader.readShort() & 0xffff);

    List<CharsRef> stems = new ArrayList<>();

    IntsRef forms = dictionary.lookupWord(strippedWord, 0, length);
    if (forms != null) {
      for (int i = 0; i < forms.length; i += formStep) {
        dictionary.flagLookup.get(forms.ints[forms.offset+i], scratch);
        char wordFlags[] = Dictionary.decodeFlags(scratch);
        if (Dictionary.hasFlag(wordFlags, flag)) {
          // confusing: in this one exception, we already chained the first prefix against the second,
          // so it doesnt need to be checked against the word
          boolean chainedPrefix = dictionary.complexPrefixes && recursionDepth == 1 && prefix;
          if (chainedPrefix == false && prefixFlag >= 0 && !Dictionary.hasFlag(wordFlags, (char)prefixFlag)) {
            // see if we can chain prefix thru the suffix continuation class (only if it has any!)
            dictionary.flagLookup.get(append, scratch);
            char appendFlags[] = Dictionary.decodeFlags(scratch);
            if (!hasCrossCheckedFlag((char)prefixFlag, appendFlags, false)) {
              continue;
            }
          }
          
          // if circumfix was previously set by a prefix, we must check this suffix,
          // to ensure it has it, and vice versa
          if (dictionary.circumfix != -1) {
            dictionary.flagLookup.get(append, scratch);
            char appendFlags[] = Dictionary.decodeFlags(scratch);
            boolean suffixCircumfix = Dictionary.hasFlag(appendFlags, (char)dictionary.circumfix);
            if (circumfix != suffixCircumfix) {
              continue;
            }
          }
          
          // we are looking for a case variant, but this word does not allow it
          if (caseVariant && dictionary.keepcase != -1 && Dictionary.hasFlag(wordFlags, (char)dictionary.keepcase)) {
            continue;
          }
          // we aren't decompounding (yet)
          if (dictionary.onlyincompound != -1 && Dictionary.hasFlag(wordFlags, (char)dictionary.onlyincompound)) {
            continue;
          }
          stems.add(newStem(strippedWord, length, forms, i));
        }
      }
    }
    
    // if a circumfix flag is defined in the dictionary, and we are a prefix, we need to check if we have that flag
    if (dictionary.circumfix != -1 && !circumfix && prefix) {
      dictionary.flagLookup.get(append, scratch);
      char appendFlags[] = Dictionary.decodeFlags(scratch);
      circumfix = Dictionary.hasFlag(appendFlags, (char)dictionary.circumfix);
    }

    if (crossProduct) {
      if (recursionDepth == 0) {
        if (prefix) {
          // we took away the first prefix.
          // COMPLEXPREFIXES = true:  combine with a second prefix and another suffix 
          // COMPLEXPREFIXES = false: combine with a suffix
          stems.addAll(stem(strippedWord, length, affix, flag, flag, ++recursionDepth, dictionary.complexPrefixes && dictionary.twoStageAffix, true, true, circumfix, caseVariant));
        } else if (dictionary.complexPrefixes == false && dictionary.twoStageAffix) {
          // we took away a suffix.
          // COMPLEXPREFIXES = true: we don't recurse! only one suffix allowed
          // COMPLEXPREFIXES = false: combine with another suffix
          stems.addAll(stem(strippedWord, length, affix, flag, prefixFlag, ++recursionDepth, false, true, false, circumfix, caseVariant));
        }
      } else if (recursionDepth == 1) {
        if (prefix && dictionary.complexPrefixes) {
          // we took away the second prefix: go look for another suffix
          stems.addAll(stem(strippedWord, length, affix, flag, flag, ++recursionDepth, false, true, true, circumfix, caseVariant));
        } else if (prefix == false && dictionary.complexPrefixes == false && dictionary.twoStageAffix) {
          // we took away a prefix, then a suffix: go look for another suffix
          stems.addAll(stem(strippedWord, length, affix, flag, prefixFlag, ++recursionDepth, false, true, false, circumfix, caseVariant));
        }
      }
    }

    return stems;
  }

  /**
   * Checks if the given flag cross checks with the given array of flags
   *
   * @param flag Flag to cross check with the array of flags
   * @param flags Array of flags to cross check against.  Can be {@code null}
   * @return {@code true} if the flag is found in the array or the array is {@code null}, {@code false} otherwise
   */
  private boolean hasCrossCheckedFlag(char flag, char[] flags, boolean matchEmpty) {
    return (flags.length == 0 && matchEmpty) || Arrays.binarySearch(flags, flag) >= 0;
  }
}