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/**
 * Copyright (c) 2016-2022 Deephaven Data Labs and Patent Pending
 */
package io.deephaven.engine.table.impl.by;

import io.deephaven.engine.table.Table;
import io.deephaven.engine.table.ColumnSource;
import io.deephaven.engine.table.impl.sources.regioned.SymbolTableSource;
import io.deephaven.util.annotations.VisibleForTesting;
import org.jetbrains.annotations.NotNull;

/**
 * Stateless "control" class for giving external code (e.g. unit tests) knobs to turn w.r.t. to how aggregations should
 * be processed.
 */
@VisibleForTesting
public class AggregationControl {

    private static final int CHUNK_SIZE = ChunkedOperatorAggregationHelper.CHUNK_SIZE;
    private static final int MINIMUM_INITIAL_HASH_SIZE = CHUNK_SIZE;
    private static final double DEFAULT_MAX_LOAD_FACTOR = 0.75;
    private static final double DEFAULT_TARGET_LOAD_FACTOR = 0.70;

    public static final AggregationControl DEFAULT = new AggregationControl();
    public static final AggregationControl DEFAULT_FOR_OPERATOR = new AggregationControl() {
        @Override
        public boolean considerGrouping(@NotNull Table table, @NotNull ColumnSource[] sources) {
            return sources.length == 1;
        }
    };

    public int initialHashTableSize(@NotNull final Table inputTable) {
        // TODO: This approach relies on rehash. Maybe we should consider sampling instead.
        return MINIMUM_INITIAL_HASH_SIZE;
    }

    public double getTargetLoadFactor() {
        return DEFAULT_TARGET_LOAD_FACTOR;
    }

    public double getMaximumLoadFactor() {
        return DEFAULT_MAX_LOAD_FACTOR;
    }

    public boolean considerGrouping(@NotNull final Table inputTable, @NotNull final ColumnSource[] sources) {
        return !inputTable.isRefreshing() && sources.length == 1;
    }

    public boolean shouldProbeShift(final long shiftSize, final int numStates) {
        return shiftSize <= numStates * 2;
    }

    boolean considerSymbolTables(@NotNull final Table inputTable, final boolean useGrouping,
            @NotNull final ColumnSource[] sources) {
        return !inputTable.isRefreshing() && !useGrouping && sources.length == 1
                && SymbolTableSource.hasSymbolTable(sources[0], inputTable.getRowSet());
    }

    boolean useSymbolTableLookupCaching() {
        return false;
    }

    boolean useSymbolTables(final long inputTableSize, final long symbolTableSize) {
        // the less than vs. leq is important here, so that we do not attempt to use a symbol table for an empty table
        // which fails later on in the SymbolTableCombiner
        return symbolTableSize < inputTableSize / 2;
    }
}