/*
 * 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.spans;


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

A Spans that is formed from the ordered subspans of a SpanNearQuery
where the subspans do not overlap and have a maximum slop between them.

The formed spans only contains minimum slop matches.

The matching slop is computed from the distance(s) between
the non overlapping matching Spans.

Successive matches are always formed from the successive Spans
of the SpanNearQuery.

The formed spans may contain overlaps when the slop is at least 1.
For example, when querying using
t1 t2 t3
with slop at least 1, the fragment:
t1 t2 t1 t3 t2 t3
matches twice:
t1 t2 .. t3      
      t1 .. t2 t3
Expert:
Only public for subclassing.  Most implementations should not need this class
/**
 * A Spans that is formed from the ordered subspans of a SpanNearQuery
 * where the subspans do not overlap and have a maximum slop between them.
 * <p>
 * The formed spans only contains minimum slop matches.<br>
 * The matching slop is computed from the distance(s) between
 * the non overlapping matching Spans.<br>
 * Successive matches are always formed from the successive Spans
 * of the SpanNearQuery.
 * <p>
 * The formed spans may contain overlaps when the slop is at least 1.
 * For example, when querying using
 * <pre>t1 t2 t3</pre>
 * with slop at least 1, the fragment:
 * <pre>t1 t2 t1 t3 t2 t3</pre>
 * matches twice:
 * <pre>t1 t2 .. t3      </pre>
 * <pre>      t1 .. t2 t3</pre>
 *
 * Expert:
 * Only public for subclassing.  Most implementations should not need this class
 */
public class NearSpansOrdered extends ConjunctionSpans {

  protected int matchStart = -1;
  protected int matchEnd = -1;
  protected int matchWidth = -1;

  private final int allowedSlop;

  public NearSpansOrdered(int allowedSlop, List<Spans> subSpans) throws IOException {
    super(subSpans);
    this.atFirstInCurrentDoc = true; // -1 startPosition/endPosition also at doc -1
    this.allowedSlop = allowedSlop;
  }

  @Override
  boolean twoPhaseCurrentDocMatches() throws IOException {
    assert unpositioned();
    oneExhaustedInCurrentDoc = false;
    while (subSpans[0].nextStartPosition() != NO_MORE_POSITIONS && !oneExhaustedInCurrentDoc) {
      if (stretchToOrder() && matchWidth <= allowedSlop) {
        return atFirstInCurrentDoc = true;
      }
    }
    return false;
  }

  private boolean unpositioned() {
    for (Spans span : subSpans) {
      if (span.startPosition() != -1)
        return false;
    }
    return true;
  }

  @Override
  public int nextStartPosition() throws IOException {
    if (atFirstInCurrentDoc) {
      atFirstInCurrentDoc = false;
      return matchStart;
    }
    oneExhaustedInCurrentDoc = false;
    while (subSpans[0].nextStartPosition() != NO_MORE_POSITIONS && !oneExhaustedInCurrentDoc) {
      if (stretchToOrder() && matchWidth <= allowedSlop) {
        return matchStart;
      }
    }
    return matchStart = matchEnd = NO_MORE_POSITIONS;
  }

  
Order the subSpans within the same document by using nextStartPosition on all subSpans
after the first as little as necessary.
Return true when the subSpans could be ordered in this way,
otherwise at least one is exhausted in the current doc.
/**
   * Order the subSpans within the same document by using nextStartPosition on all subSpans
   * after the first as little as necessary.
   * Return true when the subSpans could be ordered in this way,
   * otherwise at least one is exhausted in the current doc.
   */
  private boolean stretchToOrder() throws IOException {
    Spans prevSpans = subSpans[0];
    matchStart = prevSpans.startPosition();
    assert prevSpans.startPosition() != NO_MORE_POSITIONS : "prevSpans no start position "+prevSpans;
    assert prevSpans.endPosition() != NO_MORE_POSITIONS;
    matchWidth = 0;
    for (int i = 1; i < subSpans.length; i++) {
      Spans spans = subSpans[i];
      assert spans.startPosition() != NO_MORE_POSITIONS;
      assert spans.endPosition() != NO_MORE_POSITIONS;
      if (advancePosition(spans, prevSpans.endPosition()) == NO_MORE_POSITIONS) {
        oneExhaustedInCurrentDoc = true;
        return false;
      }
      matchWidth += (spans.startPosition() - prevSpans.endPosition());
      prevSpans = spans;
    }
    matchEnd = subSpans[subSpans.length - 1].endPosition();
    return true; // all subSpans ordered and non overlapping
  }

  private static int advancePosition(Spans spans, int position) throws IOException {
    if (spans instanceof SpanNearQuery.GapSpans) {
      return ((SpanNearQuery.GapSpans)spans).skipToPosition(position);
    }
    while (spans.startPosition() < position) {
      spans.nextStartPosition();
    }
    return spans.startPosition();
  }

  @Override
  public int startPosition() {
    return atFirstInCurrentDoc ? -1 : matchStart;
  }

  @Override
  public int endPosition() {
    return atFirstInCurrentDoc ? -1 : matchEnd;
  }

  @Override
  public int width() {
    return matchWidth;
  }

  @Override
  public void collect(SpanCollector collector) throws IOException {
    for (Spans span : subSpans) {
      span.collect(collector);
    }
  }

}