/*
 * 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.index;


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

Maintains a IndexReader TermState view over IndexReader instances containing a single term. The TermStates doesn't track if the given TermState objects are valid, neither if the TermState instances refer to the same terms in the associated readers. 
@lucene.experimental
/**
 * Maintains a {@link IndexReader} {@link TermState} view over
 * {@link IndexReader} instances containing a single term. The
 * {@link TermStates} doesn't track if the given {@link TermState}
 * objects are valid, neither if the {@link TermState} instances refer to the
 * same terms in the associated readers.
 * 
 * @lucene.experimental
 */
public final class TermStates {

  private static final TermState EMPTY_TERMSTATE = new TermState() {
    @Override
    public void copyFrom(TermState other) {

    }
  };

  // Important: do NOT keep hard references to index readers
  private final Object topReaderContextIdentity;
  private final TermState[] states;
  private final Term term;  // null if stats are to be used
  private int docFreq;
  private long totalTermFreq;

  //public static boolean DEBUG = BlockTreeTermsWriter.DEBUG;

  private TermStates(Term term, IndexReaderContext context) {
    assert context != null && context.isTopLevel;
    topReaderContextIdentity = context.identity;
    docFreq = 0;
    totalTermFreq = 0;
    final int len;
    if (context.leaves() == null) {
      len = 1;
    } else {
      len = context.leaves().size();
    }
    states = new TermState[len];
    this.term = term;
  }

  
Creates an empty TermStates from a IndexReaderContext /**
   * Creates an empty {@link TermStates} from a {@link IndexReaderContext}
   */
  public TermStates(IndexReaderContext context) {
    this(null, context);
  }

  
Expert: Return whether this TermStates was built for the given IndexReaderContext. This is typically used for assertions. 
@lucene.internal
/**
   * Expert: Return whether this {@link TermStates} was built for the given
   * {@link IndexReaderContext}. This is typically used for assertions.
   * @lucene.internal
   */
  public boolean wasBuiltFor(IndexReaderContext context) {
    return topReaderContextIdentity == context.identity;
  }

  
Creates a TermStates with an initial TermState, IndexReader pair. /**
   * Creates a {@link TermStates} with an initial {@link TermState},
   * {@link IndexReader} pair.
   */
  public TermStates(IndexReaderContext context, TermState state, int ord, int docFreq, long totalTermFreq) {
    this(null, context);
    register(state, ord, docFreq, totalTermFreq);
  }

  
Creates a TermStates from a top-level IndexReaderContext and the given Term. This method will lookup the given term in all context's leaf readers and register each of the readers containing the term in the returned TermStates using the leaf reader's ordinal. 

Note: the given context must be a top-level context.
Params:
needsStats – if true then all leaf contexts will be visited up-front to collect term statistics. Otherwise, the TermState objects will be built only when requested/**
   * Creates a {@link TermStates} from a top-level {@link IndexReaderContext} and the
   * given {@link Term}. This method will lookup the given term in all context's leaf readers 
   * and register each of the readers containing the term in the returned {@link TermStates}
   * using the leaf reader's ordinal.
   * <p>
   * Note: the given context must be a top-level context.
   *
   * @param needsStats if {@code true} then all leaf contexts will be visited up-front to
   *                   collect term statistics.  Otherwise, the {@link TermState} objects
   *                   will be built only when requested
   */
  public static TermStates build(IndexReaderContext context, Term term, boolean needsStats)
      throws IOException {
    assert context != null && context.isTopLevel;
    final TermStates perReaderTermState = new TermStates(needsStats ? null : term, context);
    if (needsStats) {
      for (final LeafReaderContext ctx : context.leaves()) {
        //if (DEBUG) System.out.println("  r=" + leaves[i].reader);
        TermsEnum termsEnum = loadTermsEnum(ctx, term);
        if (termsEnum != null) {
          final TermState termState = termsEnum.termState();
          //if (DEBUG) System.out.println("    found");
          perReaderTermState.register(termState, ctx.ord, termsEnum.docFreq(), termsEnum.totalTermFreq());
        }
      }
    }
    return perReaderTermState;
  }

  private static TermsEnum loadTermsEnum(LeafReaderContext ctx, Term term) throws IOException {
    final Terms terms = ctx.reader().terms(term.field());
    if (terms != null) {
      final TermsEnum termsEnum = terms.iterator();
      if (termsEnum.seekExact(term.bytes())) {
        return termsEnum;
      }
    }
    return null;
  }

  
Clears the TermStates internal state and removes all registered TermStates /**
   * Clears the {@link TermStates} internal state and removes all
   * registered {@link TermState}s
   */
  public void clear() {
    docFreq = 0;
    totalTermFreq = 0;
    Arrays.fill(states, null);
  }

  
Registers and associates a TermState with an leaf ordinal. The leaf ordinal should be derived from a IndexReaderContext's leaf ord. /**
   * Registers and associates a {@link TermState} with an leaf ordinal. The leaf ordinal
   * should be derived from a {@link IndexReaderContext}'s leaf ord.
   */
  public void register(TermState state, final int ord, final int docFreq, final long totalTermFreq) {
    register(state, ord);
    accumulateStatistics(docFreq, totalTermFreq);
  }

  
Expert: Registers and associates a TermState with an leaf ordinal. The leaf ordinal should be derived from a IndexReaderContext's leaf ord. On the contrary to register(TermState, int, int, long) this method does NOT update term statistics. /**
   * Expert: Registers and associates a {@link TermState} with an leaf ordinal. The
   * leaf ordinal should be derived from a {@link IndexReaderContext}'s leaf ord.
   * On the contrary to {@link #register(TermState, int, int, long)} this method
   * does NOT update term statistics.
   */
  public void register(TermState state, final int ord) {
    assert state != null : "state must not be null";
    assert ord >= 0 && ord < states.length;
    assert states[ord] == null : "state for ord: " + ord
        + " already registered";
    states[ord] = state;
  }

  
Expert: Accumulate term statistics. /** Expert: Accumulate term statistics. */
  public void accumulateStatistics(final int docFreq, final long totalTermFreq) {
    assert docFreq >= 0;
    assert totalTermFreq >= 0;
    assert docFreq <= totalTermFreq;
    this.docFreq += docFreq;
    this.totalTermFreq += totalTermFreq;
  }

  
Returns the TermState for a leaf reader context or null if no TermState for the context was registered. 
Params:
ctx –  the LeafReaderContext to get the TermState for.
Returns:
the TermState for the given readers ord or null if no TermState for the reader was registered/**
   * Returns the {@link TermState} for a leaf reader context or <code>null</code> if no
   * {@link TermState} for the context was registered.
   * 
   * @param ctx
   *          the {@link LeafReaderContext} to get the {@link TermState} for.
   * @return the {@link TermState} for the given readers ord or <code>null</code> if no
   *         {@link TermState} for the reader was registered
   */
  public TermState get(LeafReaderContext ctx) throws IOException {
    assert ctx.ord >= 0 && ctx.ord < states.length;
    if (term == null)
      return states[ctx.ord];
    if (this.states[ctx.ord] == null) {
      TermsEnum te = loadTermsEnum(ctx, term);
      this.states[ctx.ord] = te == null ? EMPTY_TERMSTATE : te.termState();
    }
    if (this.states[ctx.ord] == EMPTY_TERMSTATE)
      return null;
    return this.states[ctx.ord];
  }

  
 Returns the accumulated document frequency of all TermState instances passed to register(TermState, int, int, long). 
Returns:
the accumulated document frequency of all TermState instances passed to register(TermState, int, int, long)./**
   *  Returns the accumulated document frequency of all {@link TermState}
   *         instances passed to {@link #register(TermState, int, int, long)}.
   * @return the accumulated document frequency of all {@link TermState}
   *         instances passed to {@link #register(TermState, int, int, long)}.
   */
  public int docFreq() {
    if (term != null) {
      throw new IllegalStateException("Cannot call docFreq() when needsStats=false");
    }
    return docFreq;
  }
  
  
 Returns the accumulated term frequency of all TermState instances passed to register(TermState, int, int, long). 
Returns:
the accumulated term frequency of all TermState instances passed to register(TermState, int, int, long)./**
   *  Returns the accumulated term frequency of all {@link TermState}
   *         instances passed to {@link #register(TermState, int, int, long)}.
   * @return the accumulated term frequency of all {@link TermState}
   *         instances passed to {@link #register(TermState, int, int, long)}.
   */
  public long totalTermFreq() {
    if (term != null) {
      throw new IllegalStateException("Cannot call totalTermFreq() when needsStats=false");
    }
    return totalTermFreq;
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("TermStates\n");
    for(TermState termState : states) {
      sb.append("  state=");
      sb.append(termState);
      sb.append('\n');
    }

    return sb.toString();
  }

}