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.svl.vars;
018
019import static org.apache.juneau.commons.utils.AssertionUtils.*;
020
021import org.apache.juneau.svl.*;
022
023/**
024 * A transformational variable resolver that returns substring for given start and end (optional)
025 *
026 * <p>
027 * The format for this var is one of the following:
028 * <ul>
029 *    <li><js>"$ST{arg,start}"</js>
030 *    <li><js>"$ST{arg,start,end}"</js>
031 * </ul>
032 *
033 * <p>
034 *
035 *
036 * <h5 class='section'>Example:</h5>
037 * <p class='bjava'>
038 *    <jc>// Create a variable resolver that resolves system properties and $SW vars.</jc>
039 *    VarResolver <jv>varResolver</jv> = VarResolver.<jsm>create</jsm>().vars(SubstringVar.<jk>class</jk>, SystemPropertiesVar.<jk>class</jk>).build();
040 *
041 *    <jc>// Use it!</jc>
042 *    System.<jsf>out</jsf>.println(<jv>varResolver</jv>.resolve(<js>"Version = $ST{$P{java.version}, 0, 3}"</js>));
043 * </p>
044 *
045 * <p>
046 * Since this is a {@link MultipartVar}, any variables contained in the result will be recursively resolved.
047 * <br>Likewise, if the arguments contain any variables, those will be resolved before they are passed to this var.
048 *
049 * <h5 class='section'>See Also:</h5><ul>
050 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/SimpleVariableLanguageBasics">Simple Variable Language Basics</a>
051 * </ul>
052 */
053public class SubstringVar extends MultipartVar {
054
055   /** The name of this variable. */
056   public static final String NAME = "ST";
057
058   /**
059    * Constructor.
060    */
061   public SubstringVar() {
062      super(NAME);
063   }
064
065   @Override /* Overridden from MultipartVar */
066   public String resolve(VarResolverSession session, String[] args) {
067      assertArg(args.length >= 2 && args.length <= 3, "Invalid number of arguments passed to $ST var.  Must have 2 or 3 arguments.");
068
069      String stringArg = args[0];
070      var result = "";
071      if (args.length == 2) {
072         var start = Integer.parseInt(args[1]);
073         if (start >= 0 && start <= stringArg.length())
074            result = stringArg.substring(start);
075         if (start < 0 && -start <= stringArg.length())
076            result = stringArg.substring(stringArg.length() + start);
077      } else if (args.length == 3) {
078         var start = Integer.parseInt(args[1]);
079         var end = Integer.parseInt(args[2]);
080         if (start >= 0 && start < stringArg.length() && end >= 0 && end <= stringArg.length() && start < end)
081            result = stringArg.substring(start, end);
082      }
083      return result;
084   }
085}