001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.commons.svl.vars;
018
019import java.util.function.*;
020
021import org.apache.juneau.commons.runtime.*;
022import org.apache.juneau.commons.settings.*;
023import org.apache.juneau.commons.svl.*;
024
025/**
026 * Manifest file entries variable resolver.
027 *
028 * <p>
029 * The format for this var is <js>"$MF{key[,default]}"</js>.
030 *
031 * <p>
032 * This variable resolver requires that a {@link ManifestFile} object be made available by either:
033 * <ul class='spaced-list'>
034 *    <li>Classpath/default manifest discovery when using the no-arg constructor.
035 *    <li>Constructing the var via {@link #create(Supplier)} (per-instance).
036 * </ul>
037 *
038 * <h5 class='section'>Example:</h5>
039 * <p class='bjava'>
040 *    <jc>// Create a ManifestFile object that contains the manifest of the jar file containing this class.</jc>
041 *    ManifestFile <jv>manifestFile</jv> = <jk>new</jk> ManifestFile(<jk>this</jk>.getClass());
042 *
043 *    <jc>// Create a variable resolver that resolves manifest file entries (e.g. "$MF{Main-Class}")</jc>
044 *    VarResolver <jv>varResolver</jv> = VarResolver.<jsm>create</jsm>().vars(ManifestFileVar.<jsm>create</jsm>(() -&gt; <jv>manifestFile</jv>)).build();
045 *
046 *    <jc>// Use it!</jc>
047 *    System.<jsf>out</jsf>.println(<jv>varResolver</jv>.resolve(<js>"The main class is $MF{Main-Class}"</js>));
048 * </p>
049 *
050 * <p>
051 * Since this is a {@link SimpleVar}, any variables contained in the result will be recursively resolved.
052 * Likewise, if the arguments contain any variables, those will be resolved before they are passed to this var.
053 *
054 * <h5 class='section'>See Also:</h5><ul>
055 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/MarshallSimpleVariableLanguage">Marshall Simple Variable Language</a>
056 * </ul>
057 */
058public class ManifestFileVar extends DefaultingVar {
059
060   /** The name of this variable. */
061   public static final String NAME = "MF";
062
063   /**
064    * Creates a {@link ManifestFileVar} bound to a per-instance {@link Supplier} of {@link ManifestFile}.
065    *
066    * <p>
067    * The supplier is invoked on every resolve.
068    *
069    * @param supplier The supplier of {@link ManifestFile} for this var instance.  Must not be <jk>null</jk>.
070    * @return A new {@link ManifestFileVar} instance backed by the supplier.
071    */
072   public static ManifestFileVar create(Supplier<ManifestFile> supplier) {
073      return new ManifestFileVar(supplier);
074   }
075
076   private final ManifestFilePropertySource source;
077
078   /**
079    * Constructor.
080    */
081   public ManifestFileVar() {
082      super(NAME);
083      this.source = ManifestFilePropertySource.createDefault();
084   }
085
086   private ManifestFileVar(Supplier<ManifestFile> supplier) {
087      super(NAME);
088      this.source = new ManifestFilePropertySource(supplier);
089   }
090
091   @Override /* Overridden from Var */
092   public String resolve(VarResolverSession session, String key) {
093      var v = source.get(key);
094      return v.isPresent() ? v.value().orElse(null) : "";
095   }
096
097   /**
098    * Manifest entries are immutable for the lifetime of the classpath. This var opts in to
099    * compile-time stable-value folding.
100    *
101    * @return Always {@code true}.
102    */
103   @Override /* Overridden from Var */
104   protected boolean isStable() {
105      return true;
106   }
107}