/*
 * 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.queries.function.valuesource;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.ReaderUtil;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.ValueSource;
import org.apache.lucene.queries.function.docvalues.FloatDocValues;
import org.apache.lucene.search.IndexSearcher;

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

Scales values to be between min and max.
This implementation currently traverses all of the source values to obtain
their min and max.
This implementation currently cannot distinguish when documents have been
deleted or documents that have no value, and 0.0 values will be used for
these cases.  This means that if values are normally all greater than 0.0, one can
still end up with 0.0 as the min value to map from.  In these cases, an
appropriate map() function could be used as a workaround to change 0.0
to a value in the real range.
/**
 * Scales values to be between min and max.
 * <p>This implementation currently traverses all of the source values to obtain
 * their min and max.
 * <p>This implementation currently cannot distinguish when documents have been
 * deleted or documents that have no value, and 0.0 values will be used for
 * these cases.  This means that if values are normally all greater than 0.0, one can
 * still end up with 0.0 as the min value to map from.  In these cases, an
 * appropriate map() function could be used as a workaround to change 0.0
 * to a value in the real range.
 */
public class ScaleFloatFunction extends ValueSource {
  protected final ValueSource source;
  protected final float min;
  protected final float max;

  public ScaleFloatFunction(ValueSource source, float min, float max) {
    this.source = source;
    this.min = min;
    this.max = max;
  }

  @Override
  public String description() {
    return "scale(" + source.description() + "," + min + "," + max + ")";
  }

  private static class ScaleInfo {
    float minVal;
    float maxVal;
  }

  private ScaleInfo createScaleInfo(Map context, LeafReaderContext readerContext) throws IOException {
    final List<LeafReaderContext> leaves = ReaderUtil.getTopLevelContext(readerContext).leaves();

    float minVal = Float.POSITIVE_INFINITY;
    float maxVal = Float.NEGATIVE_INFINITY;

    for (LeafReaderContext leaf : leaves) {
      int maxDoc = leaf.reader().maxDoc();
      FunctionValues vals =  source.getValues(context, leaf);
      for (int i=0; i<maxDoc; i++) {
        if ( ! vals.exists(i) ) {
          continue;
        }
        float val = vals.floatVal(i);
        if ((Float.floatToRawIntBits(val) & (0xff<<23)) == 0xff<<23) {
          // if the exponent in the float is all ones, then this is +Inf, -Inf or NaN
          // which don't make sense to factor into the scale function
          continue;
        }
        if (val < minVal) {
          minVal = val;
        }
        if (val > maxVal) {
          maxVal = val;
        }
      }
    }

    if (minVal == Float.POSITIVE_INFINITY) {
    // must have been an empty index
      minVal = maxVal = 0;
    }

    ScaleInfo scaleInfo = new ScaleInfo();
    scaleInfo.minVal = minVal;
    scaleInfo.maxVal = maxVal;
    context.put(ScaleFloatFunction.this, scaleInfo);
    return scaleInfo;
  }

  @Override
  public FunctionValues getValues(Map context, LeafReaderContext readerContext) throws IOException {

    ScaleInfo scaleInfo = (ScaleInfo)context.get(ScaleFloatFunction.this);
    if (scaleInfo == null) {
      scaleInfo = createScaleInfo(context, readerContext);
    }

    final float scale = (scaleInfo.maxVal-scaleInfo.minVal==0) ? 0 : (max-min)/(scaleInfo.maxVal-scaleInfo.minVal);
    final float minSource = scaleInfo.minVal;
    final float maxSource = scaleInfo.maxVal;

    final FunctionValues vals =  source.getValues(context, readerContext);

    return new FloatDocValues(this) {
      @Override
      public boolean exists(int doc) throws IOException {
        return vals.exists(doc);
      }
      @Override
      public float floatVal(int doc) throws IOException {
        return (vals.floatVal(doc) - minSource) * scale + min;
      }
      @Override
      public String toString(int doc) throws IOException {
        return "scale(" + vals.toString(doc) + ",toMin=" + min + ",toMax=" + max
                + ",fromMin=" + minSource
                + ",fromMax=" + maxSource
                + ")";
      }
    };
  }

  @Override
  public void createWeight(Map context, IndexSearcher searcher) throws IOException {
    source.createWeight(context, searcher);
  }

  @Override
  public int hashCode() {
    int h = Float.floatToIntBits(min);
    h = h*29;
    h += Float.floatToIntBits(max);
    h = h*29;
    h += source.hashCode();
    return h;
  }

  @Override
  public boolean equals(Object o) {
    if (ScaleFloatFunction.class != o.getClass()) return false;
    ScaleFloatFunction other = (ScaleFloatFunction)o;
    return this.min == other.min
         && this.max == other.max
         && this.source.equals(other.source);
  }
}