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Reference implementation for j(s)-lib template API, declarative, natural and based on X(HT)ML language.

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package js.template.xhtml;

import js.dom.Element;
import js.lang.Pair;
import js.lang.PairsList;
import js.template.TemplateException;

/**
 * Add or remove element CSS class considering conditional expression value. In sample code there are two class expressions
 * evaluated in natural order. If conditional expression is true add related class otherwise remove it. In example, if
 * type value is DIRECTORY add CSS class directory to div element otherwise
 * add file class.
 * 
 * 
 * 
 *  <div data-css-class="type=DIRECTORY:directory;!type=DIRECTORY:file;" />
 * 
 * 
 * Operand is a list of semicolon separated CSS class expressions, see syntax below. A class expression has a conditional
 * expression as described by {@link ConditionalExpression} class description and a CSS class name separated by colon.
 * 
 * 
 * 
 *    operand = class-expression *( ';' class-expression ) [ ';' ]
 *    class-expression = conditional-expression ':' class-name
 *    
 *    ; conditional-expression = see conditional expression class description
 *    ; class-name = CSS class name
 * 
 * 
 * @author Iulian Rotaru
 */
final class CssClassOperator extends Operator {
	/** Dynamic content reference. */
	private Content content;

	/**
	 * Construct CSS_CLASS operator instance.
	 * 
	 * @param serializer parent serializer,
	 * @param content dynamic content.
	 */
	CssClassOperator(Serializer serializer, Content content) {
		this.content = content;
	}

	@Override
	protected Object doExec(Element element, Object scope, String expression, Object... arguments) throws TemplateException {
		if (expression.isEmpty()) {
			throw new TemplateException("Invalid CSS_CLASS operand. Expression is empty.");
		}

		CssClass cssClass = new CssClass(element);
		PairsList pairs = new PairsList(expression);

		for (Pair pair : pairs) {
			// accordingly CSS_CLASS operator syntax first pair value is a conditional expression and the second is the CSS
			// class name

			ConditionalExpression conditionalExpression = new ConditionalExpression(content, scope, pair.first());
			String className = pair.second();

			if (conditionalExpression.value()) {
				log.debug("True conditional expression |%s|. Add CSS class |%s| to element |%s|.", pair.first(), className, element.trace());
				cssClass.add(className);
			} else {
				log.debug("False conditional expression |%s|. Remove CSS class |%s| from element |%s|.", pair.first(), className, element.trace());
				cssClass.remove(className);
			}
		}

		return cssClass;
	}
}