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/*
 Copyright 2013 Red Hat, Inc. and/or its affiliates.

 This file is part of lightblue.

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program.  If not, see .
 */
package com.redhat.lightblue.eval;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.NullNode;
import com.redhat.lightblue.crud.CrudConstants;
import com.redhat.lightblue.metadata.FieldTreeNode;
import com.redhat.lightblue.query.ValueComparisonExpression;
import com.redhat.lightblue.query.BinaryComparisonOperator;
import com.redhat.lightblue.query.Value;
import com.redhat.lightblue.util.Path;
import com.redhat.lightblue.util.KeyValueCursor;

public class ValueComparisonEvaluator extends QueryEvaluator {

    private static final Logger LOGGER = LoggerFactory.getLogger(ValueComparisonEvaluator.class);

    private final FieldTreeNode fieldMd;
    private final Path field;
    private final BinaryComparisonOperator operator;
    private final Value rvalue;

    /**
     * Constructs evaluator for {field op value} style comparison
     *
     * @param expr The expression
     * @param md Entity metadata
     */
    public ValueComparisonEvaluator(ValueComparisonExpression expr, FieldTreeNode context) {
        this.field = expr.getField();
        fieldMd = context.resolve(field);
        if (fieldMd == null) {
            throw new EvaluationError(expr, CrudConstants.ERR_FIELD_NOT_THERE + field);
        }
        operator = expr.getOp();
        rvalue = expr.getRvalue();
        LOGGER.debug("ctor {} {}", field, operator);
    }

    @Override
    public boolean evaluate(QueryEvaluationContext ctx) {
        ctx.setResult(false);
        Object value = rvalue.getValue();
        LOGGER.debug("evaluate {} {} {}", field, operator, value);
        KeyValueCursor cursor = ctx.getNodes(field);
        boolean fieldValueExists = false;
        while (cursor.hasNext()) {
            fieldValueExists = true;
            cursor.next();
            JsonNode valueNode = cursor.getCurrentValue();
            int result;
            if (value == null) {
                // Comparing to null, we don't need the docValue, all we need is if docValue is null or not
                boolean docValueNull = valueNode == null || valueNode instanceof NullNode;
                if (docValueNull) {
                    result = 0;
                } else {
                    result = -1;
                }

            } else {
                Object docValue;
                if (valueNode != null) {
                    docValue = fieldMd.getType().fromJson(valueNode);
                } else {
                    docValue = null;
                }
                LOGGER.debug(" fieldvalue={} value={} type={}", docValue, value, fieldMd.getType().getName());
                result = fieldMd.getType().compare(docValue, value);
            }
            LOGGER.debug(" result={}", result);
            ctx.setResult(operator.apply(result));
            if (ctx.getResult()) {
                break;
            }
        }
        // If we're comparing equivalence to null, nonexistance of a field matches
        if (value == null && !fieldValueExists && operator == BinaryComparisonOperator._eq) {
            ctx.setResult(true);
        }
        return ctx.getResult();
    }
}