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package org.apache.juneau.svl.vars;

import static org.apache.juneau.assertions.Assertions.*;
import java.util.regex.*;

import org.apache.juneau.svl.*;

/**
 * A transformational variable resolver that returns character count or list count (using given delimiter).
 *
 * <p>
 * The format for this var is one of the following:
 * <ul>
 * 	<li><js>"$LN{arg}"</js>
 * 	<li><js>"$LN{arg,delimiter}"</js>
 * </ul>
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bjava'>
 * 	<jc>// Create a variable resolver that resolves system properties and $SW vars.</jc>
 * 	VarResolver <jv>varResolver</jv> = VarResolver.<jsm>create</jsm>().vars(LenVar.<jk>class</jk>, SystemPropertiesVar.<jk>class</jk>).build();
 *
 * 	<jc>// Use it!</jc>
 * 	System.<jsf>out</jsf>.println(<jv>varResolver</jv>.resolve(<js>"Parts = $LN{$P{os.version},.} Chars = $LN{$P{os.version}}"</js>));
 * </p>
 *
 * <p>
 * Since this is a {@link MultipartVar}, any variables contained in the result will be recursively resolved.
 * <br>Likewise, if the arguments contain any variables, those will be resolved before they are passed to this var.
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc jm.SimpleVariableLanguage}
 * 	<li class='extlink'>{@source}
 * </ul>
 */
public class LenVar extends MultipartVar {

	/** The name of this variable. */
	public static final String NAME = "LN";

	/**
	 * Constructor.
	 */
	public LenVar() {
		super(NAME);
	}

	@Override /* MultipartVar */
	public String resolve(VarResolverSession session, String[] args) {
		assertArg(args.length <= 2, "Invalid number of arguments passed to $LN var.  Must have 1 or 2 arguments.");

		int len = 0;
		String stringArg = args[0];
		if (args.length == 1)
			len = stringArg.length();
		else if (args.length == 2) {
			//delimiter is given
			String delimiter = Pattern.quote(args[1]);
			len = stringArg.trim().split(delimiter).length;
		}
		return String.valueOf(len);
	}
}
