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package org.apache.juneau.svl.vars;

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

/**
 * Manifest file entries variable resolver.
 *
 * <p>
 * The format for this var is <js>"$MF{key[,default]}"</js>.
 *
 * <p>
 * This variable resolver requires that a {@link ManifestFile} object be made available by calling
 * the {@link #init(ManifestFile)} method.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bcode w800'>
 * 	<jc>// Create a ManifestFile object that contains the manifest of the jar file containing this class.</jc>
 * 	ManifestFile mf = <jk>new</jk> ManifestFile(<jk>this</jk>.getClass());
 *
 * 	ManifestFileVar.<jsm>init</jsm>(mf);
 *
 * 	<jc>// Create a variable resolver that resolves manifest file entries (e.g. "$MF{Main-Class}")</jc>
 * 	VarResolver r = <jk>new</jk> VarResolver().addVars(ManifestFile.<js>class</js>);
 *
 * 	<jc>// Use it!</jc>
 * 	System.<jsf>out</jsf>.println(r.resolve(<js>"The main class is $MF{Main-Class}"</js>));
 * </p>
 *
 * <p>
 * Since this is a {@link SimpleVar}, any variables contained in the result will be recursively resolved.
 * Likewise, if the arguments contain any variables, those will be resolved before they are passed to this var.
 *
 * @see org.apache.juneau.utils.ManifestFile
 * @see org.apache.juneau.svl
 */
public class ManifestFileVar extends DefaultingVar {

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

	private static volatile ManifestFile MANIFEST_FILE;

	/**
	 * Initialize the manifest file for this variable.
	 *
	 * @param manifestFile The parsed manifest file.
	 */
	public static void init(ManifestFile manifestFile) {
		MANIFEST_FILE = manifestFile;
	}

	private final ManifestFile manifestFile;

	/**
	 * Constructor.
	 */
	public ManifestFileVar() {
		super(NAME);
		this.manifestFile = MANIFEST_FILE;
	}

	@Override /* Var */
	public String resolve(VarResolverSession session, String key) {
		return manifestFile == null ? "" : manifestFile.getString(key);
	}
}
