/*
 ***************************************************************************************
 *  Copyright (C) 2006 EsperTech, Inc. All rights reserved.                            *
 *  http://www.espertech.com/esper                                                     *
 *  http://www.espertech.com                                                           *
 *  ---------------------------------------------------------------------------------- *
 *  The software in this package is published under the terms of the GPL license       *
 *  a copy of which has been included with this distribution in the license.txt file.  *
 ***************************************************************************************
 */
package com.espertech.esper.filter;

import com.espertech.esper.util.MetaDefItem;

import java.io.Serializable;
import java.util.Comparator;

/**
 * Sort comparator for filter parameters that sorts filter parameters according to filter operator type.
 */
public class FilterSpecParamComparator implements Comparator<FilterOperator>, MetaDefItem, Serializable {
    /**
     * Defines the sort order among filter operator types. The idea is to sort EQUAL-type operators first
     * then RANGE then other operators, ie. sorting from a more restrictive (usually, not necessarily,
     * really depends on the client application) to a less restrictive operand.
     */
    private static final FilterOperator[] FILTER_OPERATOR_SORT_ORDER = {
        FilterOperator.EQUAL,
        FilterOperator.IS,
        FilterOperator.IN_LIST_OF_VALUES,
        FilterOperator.ADVANCED_INDEX,
        FilterOperator.RANGE_OPEN,
        FilterOperator.RANGE_HALF_OPEN,
        FilterOperator.RANGE_HALF_CLOSED,
        FilterOperator.RANGE_CLOSED,
        FilterOperator.LESS,
        FilterOperator.LESS_OR_EQUAL,
        FilterOperator.GREATER_OR_EQUAL,
        FilterOperator.GREATER,
        FilterOperator.NOT_RANGE_CLOSED,
        FilterOperator.NOT_RANGE_HALF_CLOSED,
        FilterOperator.NOT_RANGE_HALF_OPEN,
        FilterOperator.NOT_RANGE_OPEN,
        FilterOperator.NOT_IN_LIST_OF_VALUES,
        FilterOperator.NOT_EQUAL,
        FilterOperator.IS_NOT,
        FilterOperator.BOOLEAN_EXPRESSION
    };

    private static int[] filterSortOrder;
    private static final long serialVersionUID = -3001682034930099256L;

    static {
        filterSortOrder = new int[FilterOperator.values().length];
        for (int i = 0; i < filterSortOrder.length; i++) {
            filterSortOrder[i] = indexOf(FilterOperator.values()[i]);
        }
    }

    public int compare(FilterOperator param1, FilterOperator param2) {
        // Within the same filter operator type sort by attribute name
        if (param1 == param2) {
            return 0;
        }

        // Within different filter operator types sort by the table above
        int opIndex1 = filterSortOrder[param1.ordinal()];
        int opIndex2 = filterSortOrder[param2.ordinal()];

        if (opIndex1 < opIndex2) {
            return -1;
        } else {
            return 1;
        }
    }

    private static int indexOf(FilterOperator filterOperator) {
        for (int i = 0; i < FILTER_OPERATOR_SORT_ORDER.length; i++) {
            if (FILTER_OPERATOR_SORT_ORDER[i] == filterOperator) {
                return i;
            }
        }

        return FILTER_OPERATOR_SORT_ORDER.length;
    }
}