/*
 *  Copyright 2023 the original author or authors.
 *
 *  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
 *
 *       https://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 rife.render;

import rife.template.Template;
import rife.template.ValueRenderer;

/**
 * <p>Swap case of a template value.</p>
 *
 * <p>Usage:</p>
 *
 * <pre>
 *   &lt;!--v render:rife.render.SwapCase:valueId/--&gt;
 *   {{v render:rife.render.SwapCase:valueId/}}
 * </pre>
 *
 * @author <a href="https://erik.thauvin.net/">Erik C. Thauvin</a>
 * @since 1.0
 */
public class SwapCase implements ValueRenderer {
    /**
     * Swaps the case of a String.
     *
     * @param src the String to swap the case of
     * @return the modified String or null
     */
    public static String swapCase(final String src) {
        if (src == null || src.isEmpty()) {
            return src;
        }

        int offset = 0;
        var len = src.length();
        var buff = new int[len];
        for (var i = 0; i < len; ) {
            int newCodePoint;
            var curCodePoint = src.codePointAt(i);
            if (Character.isUpperCase(curCodePoint) || Character.isTitleCase(curCodePoint)) {
                newCodePoint = Character.toLowerCase(curCodePoint);
            } else if (Character.isLowerCase(curCodePoint)) {
                newCodePoint = Character.toUpperCase(curCodePoint);
            } else {
                newCodePoint = curCodePoint;
            }
            buff[offset++] = newCodePoint;
            i += Character.charCount(newCodePoint);
        }
        return new String(buff, 0, offset);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String render(Template template, String valueId, String differentiator) {
        if (template.hasValueId(differentiator)) {
            return swapCase(template.getValue(differentiator));
        } else {
            return "";
        }
    }
}