/*
 * 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.facet;

import java.io.IOException;
import java.util.Collection;
import java.util.Collections;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.search.BulkScorer;
import org.apache.lucene.search.Collector;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.LeafCollector;
import org.apache.lucene.search.Scorable;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.TwoPhaseIterator;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.FixedBitSet;

class DrillSidewaysScorer extends BulkScorer {

  //private static boolean DEBUG = false;

  private final Collector drillDownCollector;
  private LeafCollector drillDownLeafCollector;

  private final DocsAndCost[] dims;

  // DrillDown DocsEnums:
  private final Scorer baseScorer;
  private final DocIdSetIterator baseIterator;

  private final LeafReaderContext context;

  final boolean scoreSubDocsAtOnce;

  private static final int CHUNK = 2048;
  private static final int MASK = CHUNK-1;

  private int collectDocID = -1;
  private float collectScore;

  DrillSidewaysScorer(LeafReaderContext context, Scorer baseScorer, Collector drillDownCollector,
                      DocsAndCost[] dims, boolean scoreSubDocsAtOnce) {
    this.dims = dims;
    this.context = context;
    this.baseScorer = baseScorer;
    this.baseIterator = baseScorer.iterator();
    this.drillDownCollector = drillDownCollector;
    this.scoreSubDocsAtOnce = scoreSubDocsAtOnce;
  }

  @Override
  public long cost() {
    return baseIterator.cost();
  }

  @Override
  public int score(LeafCollector collector, Bits acceptDocs, int min, int maxDoc) throws IOException {
    if (min != 0) {
      throw new IllegalArgumentException("min must be 0, got " + min);
    }
    if (maxDoc != Integer.MAX_VALUE) {
      throw new IllegalArgumentException("maxDoc must be Integer.MAX_VALUE");
    }
    //if (DEBUG) {
    //  System.out.println("\nscore: reader=" + context.reader());
    //}
    //System.out.println("score r=" + context.reader());
    ScoreAndDoc scorer = new ScoreAndDoc();
    collector.setScorer(scorer);
    if (drillDownCollector != null) {
      drillDownLeafCollector = drillDownCollector.getLeafCollector(context);
      drillDownLeafCollector.setScorer(scorer);
    } else {
      drillDownLeafCollector = null;
    }
    for (DocsAndCost dim : dims) {
      dim.sidewaysLeafCollector = dim.sidewaysCollector.getLeafCollector(context);
      dim.sidewaysLeafCollector.setScorer(scorer);
    }

    // some scorers, eg ReqExlScorer, can hit NPE if cost is called after nextDoc
    long baseQueryCost = baseIterator.cost();

    final int numDims = dims.length;

    long drillDownCost = 0;
    for (int dim=0;dim<numDims;dim++) {
      drillDownCost += dims[dim].approximation.cost();
    }

    long drillDownAdvancedCost = 0;
    if (numDims > 1) {
      drillDownAdvancedCost = dims[1].approximation.cost();
    }

    // Position all scorers to their first matching doc:
    baseIterator.nextDoc();
    for (DocsAndCost dim : dims) {
      dim.approximation.nextDoc();
    }

    /*
    System.out.println("\nbaseDocID=" + baseScorer.docID() + " est=" + estBaseHitCount);
    System.out.println("  maxDoc=" + context.reader().maxDoc());
    System.out.println("  maxCost=" + maxCost);
    System.out.println("  dims[0].freq=" + dims[0].freq);
    if (numDims > 1) {
      System.out.println("  dims[1].freq=" + dims[1].freq);
    }
    */

    if (scoreSubDocsAtOnce || baseQueryCost < drillDownCost/10) {
      //System.out.println("queryFirst: baseScorer=" + baseScorer + " disis.length=" + disis.length + " bits.length=" + bits.length);
      doQueryFirstScoring(acceptDocs, collector, dims);
    } else if (numDims > 1 && drillDownAdvancedCost < baseQueryCost/10) {
      //System.out.println("drillDownAdvance");
      doDrillDownAdvanceScoring(acceptDocs, collector, dims);
    } else {
      //System.out.println("union");
      doUnionScoring(acceptDocs, collector, dims);
    }

    return Integer.MAX_VALUE;
  }

  
Used when base query is highly constraining vs the
 drilldowns, or when the docs must be scored at once
 (i.e., like BooleanScorer2, not BooleanScorer).  In
 this case we just .next() on base and .advance() on
 the dim filters. /** Used when base query is highly constraining vs the
   *  drilldowns, or when the docs must be scored at once
   *  (i.e., like BooleanScorer2, not BooleanScorer).  In
   *  this case we just .next() on base and .advance() on
   *  the dim filters. */ 
  private void doQueryFirstScoring(Bits acceptDocs, LeafCollector collector, DocsAndCost[] dims) throws IOException {
    //if (DEBUG) {
    //  System.out.println("  doQueryFirstScoring");
    //}
    int docID = baseScorer.docID();

    nextDoc: while (docID != PostingsEnum.NO_MORE_DOCS) {
      if (acceptDocs != null && acceptDocs.get(docID) == false) {
        docID = baseIterator.nextDoc();
        continue;
      }
      LeafCollector failedCollector = null;
      for (DocsAndCost dim : dims) {
        // TODO: should we sort this 2nd dimension of
        // docsEnums from most frequent to least?
        if (dim.approximation.docID() < docID) {
          dim.approximation.advance(docID);
        }

        boolean matches = false;
        if (dim.approximation.docID() == docID) {
          if (dim.twoPhase == null) {
            matches = true;
          } else {
            matches = dim.twoPhase.matches();
          }
        }

        if (matches == false) {
          if (failedCollector != null) {
            // More than one dim fails on this document, so
            // it's neither a hit nor a near-miss; move to
            // next doc:
            docID = baseIterator.nextDoc();
            continue nextDoc;
          } else {
            failedCollector = dim.sidewaysLeafCollector;
          }
        }
      }

      collectDocID = docID;

      // TODO: we could score on demand instead since we are
      // daat here:
      collectScore = baseScorer.score();

      if (failedCollector == null) {
        // Hit passed all filters, so it's "real":
        collectHit(collector, dims);
      } else {
        // Hit missed exactly one filter:
        collectNearMiss(failedCollector);
      }

      docID = baseIterator.nextDoc();
    }
  }

  
Used when drill downs are highly constraining vs
 baseQuery. /** Used when drill downs are highly constraining vs
   *  baseQuery. */
  private void doDrillDownAdvanceScoring(Bits acceptDocs, LeafCollector collector, DocsAndCost[] dims) throws IOException {
    final int maxDoc = context.reader().maxDoc();
    final int numDims = dims.length;

    //if (DEBUG) {
    //  System.out.println("  doDrillDownAdvanceScoring");
    //}

    // TODO: maybe a class like BS, instead of parallel arrays
    int[] filledSlots = new int[CHUNK];
    int[] docIDs = new int[CHUNK];
    float[] scores = new float[CHUNK];
    int[] missingDims = new int[CHUNK];
    int[] counts = new int[CHUNK];

    docIDs[0] = -1;
    int nextChunkStart = CHUNK;

    final FixedBitSet seen = new FixedBitSet(CHUNK);

    while (true) {
      //if (DEBUG) {
      //  System.out.println("\ncycle nextChunkStart=" + nextChunkStart + " docIds[0]=" + docIDs[0]);
      //}

      // First dim:
      //if (DEBUG) {
      //  System.out.println("  dim0");
      //}
      DocsAndCost dc = dims[0];
      int docID = dc.approximation.docID();
      while (docID < nextChunkStart) {
        if (acceptDocs == null || acceptDocs.get(docID)) {
          int slot = docID & MASK;

          if (docIDs[slot] != docID && (dc.twoPhase == null || dc.twoPhase.matches())) {
            seen.set(slot);
            // Mark slot as valid:
            //if (DEBUG) {
            //  System.out.println("    set docID=" + docID + " id=" + context.reader().document(docID).get("id"));
            //}
            docIDs[slot] = docID;
            missingDims[slot] = 1;
            counts[slot] = 1;
          }
        }

        docID = dc.approximation.nextDoc();
      }
      
      // Second dim:
      //if (DEBUG) {
      //  System.out.println("  dim1");
      //}
      dc = dims[1];
      docID = dc.approximation.docID();
      while (docID < nextChunkStart) {
        if (acceptDocs == null || acceptDocs.get(docID)
            && (dc.twoPhase == null || dc.twoPhase.matches())) {
          int slot = docID & MASK;

          if (docIDs[slot] != docID) {
            // Mark slot as valid:
            seen.set(slot);
            //if (DEBUG) {
            //  System.out.println("    set docID=" + docID + " missingDim=0 id=" + context.reader().document(docID).get("id"));
            //}
            docIDs[slot] = docID;
            missingDims[slot] = 0;
            counts[slot] = 1;
          } else {
            // TODO: single-valued dims will always be true
            // below; we could somehow specialize
            if (missingDims[slot] >= 1) {
              missingDims[slot] = 2;
              counts[slot] = 2;
              //if (DEBUG) {
              //  System.out.println("    set docID=" + docID + " missingDim=2 id=" + context.reader().document(docID).get("id"));
              //}
            } else {
              counts[slot] = 1;
              //if (DEBUG) {
              //  System.out.println("    set docID=" + docID + " missingDim=" + missingDims[slot] + " id=" + context.reader().document(docID).get("id"));
              //}
            }
          }
        }

        docID = dc.approximation.nextDoc();
      }

      // After this we can "upgrade" to conjunction, because
      // any doc not seen by either dim 0 or dim 1 cannot be
      // a hit or a near miss:

      //if (DEBUG) {
      //  System.out.println("  baseScorer");
      //}

      // Fold in baseScorer, using advance:
      int filledCount = 0;
      int slot0 = 0;
      while (slot0 < CHUNK && (slot0 = seen.nextSetBit(slot0)) != DocIdSetIterator.NO_MORE_DOCS) {
        int ddDocID = docIDs[slot0];
        assert ddDocID != -1;

        int baseDocID = baseIterator.docID();
        if (baseDocID < ddDocID) {
          baseDocID = baseIterator.advance(ddDocID);
        }
        if (baseDocID == ddDocID) {
          //if (DEBUG) {
          //  System.out.println("    keep docID=" + ddDocID + " id=" + context.reader().document(ddDocID).get("id"));
          //}
          scores[slot0] = baseScorer.score();
          filledSlots[filledCount++] = slot0;
          counts[slot0]++;
        } else {
          //if (DEBUG) {
          //  System.out.println("    no docID=" + ddDocID + " id=" + context.reader().document(ddDocID).get("id"));
          //}
          docIDs[slot0] = -1;

          // TODO: we could jump slot0 forward to the
          // baseDocID ... but we'd need to set docIDs for
          // intervening slots to -1
        }
        slot0++;
      }
      seen.clear(0, CHUNK);

      if (filledCount == 0) {
        if (nextChunkStart >= maxDoc) {
          break;
        }
        nextChunkStart += CHUNK;
        continue;
      }
      
      // TODO: factor this out & share w/ union scorer,
      // except we start from dim=2 instead:
      for (int dim=2;dim<numDims;dim++) {
        //if (DEBUG) {
        //  System.out.println("  dim=" + dim + " [" + dims[dim].dim + "]");
        //}
        dc = dims[dim];
        docID = dc.approximation.docID();
        while (docID < nextChunkStart) {
          int slot = docID & MASK;
          if (docIDs[slot] == docID
              && counts[slot] >= dim
              && (dc.twoPhase == null || dc.twoPhase.matches())) {
            // TODO: single-valued dims will always be true
            // below; we could somehow specialize
            if (missingDims[slot] >= dim) {
              //if (DEBUG) {
              //  System.out.println("    set docID=" + docID + " count=" + (dim+2));
              //}
              missingDims[slot] = dim+1;
              counts[slot] = dim+2;
            } else {
              //if (DEBUG) {
              //  System.out.println("    set docID=" + docID + " missing count=" + (dim+1));
              //}
              counts[slot] = dim+1;
            }
          }

          // TODO: sometimes use advance?
          docID = dc.approximation.nextDoc();
        }
      }

      // Collect:
      //if (DEBUG) {
      //  System.out.println("  now collect: " + filledCount + " hits");
      //}
      for (int i=0;i<filledCount;i++) {
        int slot = filledSlots[i];
        collectDocID = docIDs[slot];
        collectScore = scores[slot];
        //if (DEBUG) {
        //  System.out.println("    docID=" + docIDs[slot] + " count=" + counts[slot]);
        //}
        if (counts[slot] == 1+numDims) {
          collectHit(collector, dims);
        } else if (counts[slot] == numDims) {
          collectNearMiss(dims[missingDims[slot]].sidewaysLeafCollector);
        }
      }

      if (nextChunkStart >= maxDoc) {
        break;
      }

      nextChunkStart += CHUNK;
    }
  }

  private void doUnionScoring(Bits acceptDocs, LeafCollector collector, DocsAndCost[] dims) throws IOException {
    //if (DEBUG) {
    //  System.out.println("  doUnionScoring");
    //}

    final int maxDoc = context.reader().maxDoc();
    final int numDims = dims.length;

    // TODO: maybe a class like BS, instead of parallel arrays
    int[] filledSlots = new int[CHUNK];
    int[] docIDs = new int[CHUNK];
    float[] scores = new float[CHUNK];
    int[] missingDims = new int[CHUNK];
    int[] counts = new int[CHUNK];

    docIDs[0] = -1;

    // NOTE: this is basically a specialized version of
    // BooleanScorer, to the minShouldMatch=N-1 case, but
    // carefully tracking which dimension failed to match

    int nextChunkStart = CHUNK;

    while (true) {
      //if (DEBUG) {
      //  System.out.println("\ncycle nextChunkStart=" + nextChunkStart + " docIds[0]=" + docIDs[0]);
      //}
      int filledCount = 0;
      int docID = baseIterator.docID();
      //if (DEBUG) {
      //  System.out.println("  base docID=" + docID);
      //}
      while (docID < nextChunkStart) {
        if (acceptDocs == null || acceptDocs.get(docID)) {
          int slot = docID & MASK;
          //if (DEBUG) {
          //  System.out.println("    docIDs[slot=" + slot + "]=" + docID + " id=" + context.reader().document(docID).get("id"));
          //}

          // Mark slot as valid:
          assert docIDs[slot] != docID: "slot=" + slot + " docID=" + docID;
          docIDs[slot] = docID;
          scores[slot] = baseScorer.score();
          filledSlots[filledCount++] = slot;
          missingDims[slot] = 0;
          counts[slot] = 1;
        }
        docID = baseIterator.nextDoc();
      }

      if (filledCount == 0) {
        if (nextChunkStart >= maxDoc) {
          break;
        }
        nextChunkStart += CHUNK;
        continue;
      }

      // First drill-down dim, basically adds SHOULD onto
      // the baseQuery:
      //if (DEBUG) {
      //  System.out.println("  dim=0 [" + dims[0].dim + "]");
      //}
      {
        DocsAndCost dc = dims[0];
        docID = dc.approximation.docID();
        //if (DEBUG) {
        //  System.out.println("    start docID=" + docID);
        //}
        while (docID < nextChunkStart) {
          int slot = docID & MASK;
          if (docIDs[slot] == docID // this also checks that the doc is not deleted
              && (dc.twoPhase == null || dc.twoPhase.matches())) {
            //if (DEBUG) {
            //  System.out.println("      set docID=" + docID + " count=2");
            //}
            missingDims[slot] = 1;
            counts[slot] = 2;
          }
          docID = dc.approximation.nextDoc();
        }
      }

      for (int dim=1;dim<numDims;dim++) {
        //if (DEBUG) {
        //  System.out.println("  dim=" + dim + " [" + dims[dim].dim + "]");
        //}

        DocsAndCost dc = dims[dim];
        docID = dc.approximation.docID();
        //if (DEBUG) {
        //  System.out.println("    start docID=" + docID);
        //}
        while (docID < nextChunkStart) {
          int slot = docID & MASK;
          if (docIDs[slot] == docID // also means that the doc is not deleted
              && counts[slot] >= dim
              && (dc.twoPhase == null || dc.twoPhase.matches())) {
            // This doc is still in the running...
            // TODO: single-valued dims will always be true
            // below; we could somehow specialize
            if (missingDims[slot] >= dim) {
              //if (DEBUG) {
              //  System.out.println("      set docID=" + docID + " count=" + (dim+2));
              //}
              missingDims[slot] = dim+1;
              counts[slot] = dim+2;
            } else {
              //if (DEBUG) {
              //  System.out.println("      set docID=" + docID + " missing count=" + (dim+1));
              //}
              counts[slot] = dim+1;
            }
          }
          docID = dc.approximation.nextDoc();
        }
      }

      // Collect:
      //System.out.println("  now collect: " + filledCount + " hits");
      for (int i=0;i<filledCount;i++) {
        // NOTE: This is actually in-order collection,
        // because we only accept docs originally returned by
        // the baseScorer (ie that Scorer is AND'd)
        int slot = filledSlots[i];
        collectDocID = docIDs[slot];
        collectScore = scores[slot];
        //if (DEBUG) {
        //  System.out.println("    docID=" + docIDs[slot] + " count=" + counts[slot]);
        //}
        //System.out.println("  collect doc=" + collectDocID + " main.freq=" + (counts[slot]-1) + " main.doc=" + collectDocID + " exactCount=" + numDims);
        if (counts[slot] == 1+numDims) {
          //System.out.println("    hit");
          collectHit(collector, dims);
        } else if (counts[slot] == numDims) {
          //System.out.println("    sw");
          collectNearMiss(dims[missingDims[slot]].sidewaysLeafCollector);
        }
      }

      if (nextChunkStart >= maxDoc) {
        break;
      }

      nextChunkStart += CHUNK;
    }
  }

  private void collectHit(LeafCollector collector, DocsAndCost[] dims) throws IOException {
    //if (DEBUG) {
    //  System.out.println("      hit");
    //}

    collector.collect(collectDocID);
    if (drillDownCollector != null) {
      drillDownLeafCollector.collect(collectDocID);
    }

    // TODO: we could "fix" faceting of the sideways counts
    // to do this "union" (of the drill down hits) in the
    // end instead:

    // Tally sideways counts:
    for (DocsAndCost dim : dims) {
      dim.sidewaysLeafCollector.collect(collectDocID);
    }
  }

  private void collectNearMiss(LeafCollector sidewaysCollector) throws IOException {
    //if (DEBUG) {
    //  System.out.println("      missingDim=" + dim);
    //}
    sidewaysCollector.collect(collectDocID);
  }

  private final class ScoreAndDoc extends Scorable {

    @Override
    public int docID() {
      return collectDocID;
    }
    
    @Override
    public float score() {
      return collectScore;
    }

    @Override
    public Collection<ChildScorable> getChildren() {
      return Collections.singletonList(new ChildScorable(baseScorer, "MUST"));
    }

  }

  static class DocsAndCost {
    // approximation of matching docs, or the scorer itself
    final DocIdSetIterator approximation;
    // two-phase confirmation, or null if the approximation is accurate
    final TwoPhaseIterator twoPhase;
    final Collector sidewaysCollector;
    LeafCollector sidewaysLeafCollector;

    DocsAndCost(Scorer scorer, Collector sidewaysCollector) {
      final TwoPhaseIterator twoPhase = scorer.twoPhaseIterator();
      if (twoPhase == null) {
        this.approximation = scorer.iterator();
        this.twoPhase = null;
      } else {
        this.approximation = twoPhase.approximation();
        this.twoPhase = twoPhase;
      }
      this.sidewaysCollector = sidewaysCollector;
    }
  }
}