/*
 * 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.ScoreCachingWrappingScorer;
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());
    if (drillDownCollector != null) {
      drillDownLeafCollector = drillDownCollector.getLeafCollector(context);
    } else {
      drillDownLeafCollector = null;
    }
    for (DocsAndCost dim : dims) {
      dim.sidewaysLeafCollector = dim.sidewaysCollector.getLeafCollector(context);
    }

    // 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. */ 
  private void doQueryFirstScoring(Bits acceptDocs, LeafCollector collector, DocsAndCost[] dims) throws IOException {
    //if (DEBUG) {
    //  System.out.println("  doQueryFirstScoring");
    //}
    setScorer(collector, ScoreCachingWrappingScorer.wrap(baseScorer));

    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;

      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. */
  private void doDrillDownAdvanceScoring(Bits acceptDocs, LeafCollector collector, DocsAndCost[] dims) throws IOException {
    setScorer(collector, new ScoreAndDoc());

    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");
    //}
    setScorer(collector, new ScoreAndDoc());

    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 void setScorer(LeafCollector mainCollector, Scorable scorer) throws IOException {
    mainCollector.setScorer(scorer);
    if (drillDownLeafCollector != null) {
      drillDownLeafCollector.setScorer(scorer);
    }
    for (DocsAndCost dim : dims) {
      dim.sidewaysLeafCollector.setScorer(scorer);
    }
  }

  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;
    }
  }
}