nz.net.ultraq.thymeleaf.fragments.mergers.VariableDeclarationMerger Maven / Gradle / Ivy

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/* 
 * Copyright 2016, Emanuel Rabina (http://www.ultraq.net.nz/)
 * 
 * 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 nz.net.ultraq.thymeleaf.fragments.mergers;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

/**
 * Merges variable declarations in a th:with attribute processor,
 * taking the declarations in the source and overriding same-named declarations
 * in the target.
 *
 * @author Emanuel Rabina
 */
public class VariableDeclarationMerger {

    /**
     * Create variable declaration objects out of the declaration string.
     *
     * @param declarationString
     * @return A list of variable declaration objects that make up the
     * declaration string.
     */
    private static List deriveDeclarations(String declarationString) {
        String[] attributeTokens = declarationString.split(",");
        return Arrays.stream(attributeTokens).map(VariableDeclaration::new).collect(Collectors.toList());
    }

    /**
     * Merge th:with attributes so that names from the source value
     * overwrite the same names in the target value.
     */
    public String merge(String target, String source) {
        if (target == null || target.isEmpty()) {
            return source;
        }
        if (source == null || source.isEmpty()) {
            return target;
        }
        List targetDeclarations = deriveDeclarations(target);
        List sourceDeclarations = deriveDeclarations(source);

        List newDeclarations = new ArrayList<>(targetDeclarations.size() + sourceDeclarations.size());
        for (VariableDeclaration targetDeclaration : targetDeclarations) {
            VariableDeclaration override = sourceDeclarations.stream().filter(sourceDeclaration
                    -> Objects.equals(sourceDeclaration.getName(), targetDeclaration.getName())
            ).findFirst().orElse(null);
            if (override != null) {
                sourceDeclarations.remove(override);
                newDeclarations.add(override);
            } else {
                newDeclarations.add(targetDeclaration);
            }
        }
        for (VariableDeclaration targetAttributeDeclaration : sourceDeclarations) {
            newDeclarations.add(targetAttributeDeclaration);
        }

        return newDeclarations.stream().map(String::valueOf).collect(Collectors.joining(","));
    }
}