package org.infinispan.objectfilter.impl.aggregation;

import org.infinispan.objectfilter.impl.ql.AggregationFunction;

/**
 * An accumulator is a stateless object that operates on row data.
 *
 * @author anistor@redhat.com
 * @since 8.0
 */
public abstract class FieldAccumulator {

   /**
    * Input column.
    */
   protected final int inPos;

   /**
    * Output column.
    */
   protected final int outPos;

   protected FieldAccumulator(int inPos, int outPos) {
      this.inPos = inPos;
      this.outPos = outPos;
   }

   public static void init(Object[] accRow, FieldAccumulator[] accumulators) {
      for (FieldAccumulator acc : accumulators) {
         acc.init(accRow);
      }
   }

   public static void update(Object[] srcRow, Object[] accRow, FieldAccumulator[] accumulators) {
      for (FieldAccumulator acc : accumulators) {
         acc.update(accRow, srcRow[acc.inPos]);
      }
   }

   public static void merge(Object[] srcRow, Object[] accRow, FieldAccumulator[] acc) {
      for (FieldAccumulator a : acc) {
         a.merge(accRow, srcRow[a.inPos]);
      }
   }

   public static void finish(Object[] accRow, FieldAccumulator[] accumulators) {
      for (FieldAccumulator acc : accumulators) {
         acc.finish(accRow);
      }
   }

   public void init(Object[] accRow) {
   }

   public abstract void update(Object[] accRow, Object value);

   protected void merge(Object[] accRow, Object value) {
      update(accRow, value);
   }

   protected void finish(Object[] accRow) {
   }

   public static FieldAccumulator makeAccumulator(AggregationFunction aggregationType, int inColumn, int outColumn, Class<?> propertyType) {
      switch (aggregationType) {
         case SUM:
            return new SumAccumulator(inColumn, outColumn, propertyType);
         case AVG:
            return new AvgAccumulator(inColumn, outColumn, propertyType);
         case MIN:
            return new MinAccumulator(inColumn, outColumn, propertyType);
         case MAX:
            return new MaxAccumulator(inColumn, outColumn, propertyType);
         case COUNT:
            return new CountAccumulator(inColumn, outColumn);
         default:
            throw new IllegalArgumentException("Aggregation " + aggregationType.name() + " is not supported");
      }
   }

   public static Class<?> getOutputType(AggregationFunction aggregationType, Class<?> propertyType) {
      if (aggregationType == AggregationFunction.AVG) {
         return Double.class;
      } else if (aggregationType == AggregationFunction.COUNT) {
         return Long.class;
      } else if (aggregationType == AggregationFunction.SUM) {
         return SumAccumulator.getOutputType(propertyType);
      }
      return propertyType;
   }

   @Override
   public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || o.getClass() != getClass()) return false;
      FieldAccumulator other = (FieldAccumulator) o;
      return inPos == other.inPos && outPos == other.outPos;
   }

   @Override
   public int hashCode() {
      return 31 * inPos + outPos;
   }
}