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package org.apache.juneau.svl;

/**
 * Interface for the resolution of vars with a default value if the <c>resolve()</c> method returns <jk>null</jk>.
 *
 * <p>
 * For example, to resolve the system property <js>"myProperty"</js> but resolve to <js>"not found"</js> if the
 * property doesn't exist: <js>"$S{myProperty,not found}"</js>
 *
 * <p>
 * Subclasses must implement the following method:
 * <ul class='javatree'>
 * 	<li class='jm'>{@link #resolve(VarResolverSession, String)}
 * </ul>
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc jm.SimpleVariableLanguage}
 * 	<li class='extlink'>{@source}
 * </ul>
 */
public abstract class DefaultingVar extends SimpleVar {

	/**
	 * Constructor.
	 *
	 * @param name The name of this variable.
	 */
	public DefaultingVar(String name) {
		super(name);
	}

	@Override /* Var*/
	public String doResolve(VarResolverSession session, String s) throws Exception {
		int i = s.indexOf(',');
		if (i == -1)
			return resolve(session, s.trim());
		String s1 = s.substring(0, i);
		String s2 = s.length() == i ? null : s.substring(i+1);
		String v = resolve(session, s1);
		if (v == null)
			v = s2;
		return v;
	}
}
