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Core building blocks and API for the Metal library.
There is a newer version: 10.0.0
/*
 * Copyright 2013-2016 Netherlands Forensic Institute
 *
 * Licensed 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 io.parsingdata.metal.expression.comparison;

import static io.parsingdata.metal.Util.checkNotNull;

import io.parsingdata.metal.data.Environment;
import io.parsingdata.metal.data.ImmutableList;
import io.parsingdata.metal.encoding.Encoding;
import io.parsingdata.metal.expression.Expression;
import io.parsingdata.metal.expression.value.OptionalValue;
import io.parsingdata.metal.expression.value.Value;
import io.parsingdata.metal.expression.value.ValueExpression;

/**
 * Base class for all ComparisonExpression implementations.
 * 
 * Specifies two input {@link ValueExpression}s that are to be evaluated and
 * their results compared. Handles evaluation of inputs and resulting lists.
 * The abstract {@link #compare(Value, Value)} method is then called for
 * individual values.
 * 
 * The {@link #value} argument may be null, in which case it is
 * not evaluated and the output value is substituted with a list containing
 * only the {@link Value} most recently added to the {@link Environment}.
 */
public abstract class ComparisonExpression implements Expression {

    public final ValueExpression value;
    public final ValueExpression predicate;

    public ComparisonExpression(final ValueExpression value, final ValueExpression predicate) {
        this.value = value;
        this.predicate = checkNotNull(predicate, "predicate");
    }

    @Override
    public boolean eval(final Environment environment, final Encoding encoding) {
        final ImmutableList values = value == null ? ImmutableList.create(OptionalValue.of(environment.order.current())) : value.eval(environment, encoding);
        if (values.isEmpty()) { return false; }
        final ImmutableList predicates = predicate.eval(environment, encoding);
        if (values.size != predicates.size) { return false; }
        return compare(values, predicates);
    }

    private boolean compare(final ImmutableList currents, final ImmutableList predicates) {
        if (!currents.head.isPresent() || !predicates.head.isPresent()) { return false; }
        final boolean headResult = compare(currents.head.get(), predicates.head.get());
        if (!headResult || currents.tail.isEmpty()) { return headResult; }
        return compare(currents.tail, predicates.tail);
    }

    public abstract boolean compare(final Value left, final Value right);

    @Override
    public String toString() {
        return getClass().getSimpleName() + "(" + (value == null ? "" : value + ",") + predicate + ")";
    }

}