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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.template.TemplateException;

/**
 * Include DOM branch if conditional expression evaluates to true. Operand is a conditional expression. If evaluates to true, in
 * our example type value is DIRECTORY, div element and all its descendants are excluded
 * from resulting document. See {@link ConditionalExpression} for valid syntax supported by if operator.
 * 
 *  *  <div data-if="type=DIRECTORY">  
 *  . . .
 *  </div>
 * 
 * 
 * This operator can combine conditional expression and not flag to emulate if/else. Please note
 * exclamation mark from condition expression start on else branch.
 * 
 *  *  <div data-if="type=DIRECTORY">  
 *      // this branch is included if type is DIRECTORY
 *  </div>
 *  <div data-if="!type=DIRECTORY">  
 *      // this branch is included if type is not DIRECTORY
 *  </div>
 * 
 * 
 * Similarly a switch/case branch can be emulated like in sample code below:
 * 
 *  *  <div data-if="fruit=APPLE">
 *      // enable this branch if fruit is APPLE
 *  </div>
 *  <div data-if="fruit=ORANGE">
 *      // enable this branch if fruit is ORANGE
 *  </div>
 *  <div data-if="fruit=BANANA">
 *      // enable this branch if fruit is BANANA
 *  </div>
 * 
 * 
 * @author Iulian Rotaru
 */
final class IfOperator extends Operator {
	/** Dynamic content. */
	private Content content;

	/**
	 * Construct IF operator instance.
	 * 
	 * @param content dynamic content.
	 */
	IfOperator(Content content) {
		this.content = content;
	}

	/**
	 * Execute IF operator. Evaluate given expression and return evaluation result. Returned value acts as branch
	 * enabled flag.
	 * 
	 * @param element context element, unused,
	 * @param scope scope object,
	 * @param expression conditional expression,
	 * @param arguments optional arguments, not used.
	 * @return true if element and all its descendants should be included in processed document.
	 * @throws TemplateException if content value is undefined.
	 */
	@Override
	protected Object doExec(Element element, Object scope, String expression, Object... arguments) throws TemplateException {
		ConditionalExpression conditionalExpression = new ConditionalExpression(content, scope, expression);
		return conditionalExpression.value();
	}
}