juneau-core/juneau-marshall/src/main/java/org/apache/juneau/svl/vars/SwitchVar.java

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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.internal.*;
import org.apache.juneau.svl.*;

/**
 * A basic switch/case logic variable resolver.
 *
 * <p>
 * The format for this var is one of the following:
 * <ul>
 * 	<li><js>"$SW{stringArg, pattern:thenValue[, pattern:thenValue...]}"</js>
 * 	<li>...
 * </ul>
 *
 * <p>
 * The pattern can be any string optionally containing <js>'*'</js> or <js>'?'</js> representing any or one character
 * respectively.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bcode w800'>
 * 	<jc>// Create a variable resolver that resolves system properties and $SW vars.</jc>
 * 	VarResolver r = VarResolver.<jsm>create</jsm>().vars(SwitchVar.<jk>class</jk>, SystemPropertiesVar.<jk>class</jk>).build();
 *
 * 	<jc>// Use it!</jc>
 * 	System.<jsf>out</jsf>.println(r.resolve(<js>"We are running on $SW{$P{os.name},*win*:Windows,*:Something else}!"</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 SvlVariables}
 * </ul>
 */
public class SwitchVar extends MultipartVar {

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

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

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

		String stringArg = args[0];
		for (int i = 1; i < args.length; i++) {
			String pattern = args[i];

			String[] parts = StringUtils.split(pattern, ':', 2);
			assertArg(parts.length >= 2, "Invalid arguments passed to $SW var.  Each case statement must contains 'pattern:value'.");

			Pattern p = Pattern.compile(parts[0].replace("*", ".*").replace("?", "."));
			if (p.matcher(stringArg).matches())
				return parts[1];
		}

		// Nothing matched and no else clause.
		return "";
	}
}