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// ***************************************************************************************************************************
// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
// * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance            *
// * with the License.  You may obtain a copy of the License at                                                              *
// *                                                                                                                         *
// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
// *                                                                                                                         *
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// * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the License for the        *
// * specific language governing permissions and limitations under the License.                                              *
// ***************************************************************************************************************************
package org.apache.juneau.svl;

import java.io.*;
import java.util.*;

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

/**
 * Utility class for resolving variables of the form "$X{key}" in strings.
 *
 * 
 * Variables are of the form $X{key}, where X can consist of zero or more ASCII characters.
 * 
The variable key can contain anything, even nested variables that get recursively resolved.
 *
 * 

 * Variables are defined through the {@link VarResolverBuilder#vars(Class[])} method.
 *
 * 

 * The {@link Var} interface defines how variables are converted to values.
 *
 * 
Example:
 * 
 * 	public class SystemPropertiesVar extends SimpleVar {
 *
 * 		// Must have a no-arg constructor!
 * 		public SystemPropertiesVar() {
 * 			super("S");
 * 		}
 *
 * 		@Override
 * 		public String resolve(VarResolverSession session, String varVal) {
 * 			return System.getProperty(varVal);
 * 		}
 * 	}
 *
 * 	// Create a variable resolver that resolves system properties (e.g. "$S{java.home}")
 * 	VarResolver r = VarResolver.create().vars(SystemPropertiesVar.class).build();
 *
 * 	// Use it!
 * 	System.out.println(r.resolve("java.home is set to $S{java.home}"));
 * 
 *
 * See Also:
 * 
 * 	{@doc juneau-svl.VarResolvers}
 * 
 */
public class VarResolver {

	/**
	 * Default string variable resolver with support for system properties and environment variables:
	 *
	 * 
	 * 	$S{key[,default]} - {@link SystemPropertiesVar}
	 * 	
$E{key[,default]} - {@link EnvVariablesVar}
	 * 	
$A{key[,default]} - {@link ArgsVar}
	 * 	
$MF{key[,default]} - {@link ManifestFileVar}
	 * 	
$IF{arg,then[,else]} - {@link IfVar}
	 * 	
$SW{arg,pattern1:then1[,pattern2:then2...]} - {@link SwitchVar}
	 * 	
$CO{arg[,arg2...]} - {@link CoalesceVar}
	 * 	
$PM{arg,pattern} - {@link PatternMatchVar}
	 * 	
$UC{arg} - {@link UpperCaseVar}
	 * 	
$LC{arg} - {@link LowerCaseVar}
	 * 	
$NE{arg} - {@link NotEmptyVar}
	 * 
	 *
	 * @see SystemPropertiesVar
	 * @see EnvVariablesVar
	 */
	public static final VarResolver DEFAULT = new VarResolverBuilder().defaultVars().build();

	final VarResolverContext ctx;

	/**
	 * Instantiates a new clean-slate {@link VarResolverBuilder} object.
	 *
	 * 
	 * This is equivalent to simply calling new VarResolverBuilder().
	 *
	 * @return A new {@link VarResolverBuilder} object.
	 */
	public static VarResolverBuilder create() {
		return new VarResolverBuilder();
	}

	/**
	 * Constructor.
	 *
	 * @param vars The var classes
	 * @param contextObjects
	 */
	VarResolver(Class[] vars, Map contextObjects) {
		this.ctx = new VarResolverContext(vars, contextObjects);
	}

	/**
	 * Returns a new builder object using the settings in this resolver as a base.
	 *
	 * @return A new var resolver builder.
	 */
	public VarResolverBuilder builder() {
		return new VarResolverBuilder()
			.vars(ctx.getVars())
			.contextObjects(ctx.getContextObjects());
	}

	/**
	 * Returns the read-only properties on this variable resolver.
	 *
	 * @return The read-only properties on this variable resolver.
	 */
	public VarResolverContext getContext() {
		return ctx;
	}

	/**
	 * Creates a new resolver session with no session objects.
	 *
	 * 

	 * Session objects can be associated with the specified session using the {@link VarResolverSession#sessionObject(String, Object)}
	 * method.
	 *
	 * @return A new resolver session.
	 */
	public VarResolverSession createSession() {
		return new VarResolverSession(ctx, null);
	}

	/**
	 * Same as {@link #createSession()} except allows you to specify session objects as a map.
	 *
	 * @param sessionObjects The session objects to associate with the session.
	 * @return A new resolver session.
	 */
	public VarResolverSession createSession(Map sessionObjects) {
		return new VarResolverSession(ctx, sessionObjects);
	}

	/**
	 * Resolve variables in the specified string.
	 *
	 * 

	 * This is a shortcut for calling createSession(null).resolve(s);.
	 * 
This method can only be used if the string doesn't contain variables that rely on the existence of session
	 * variables.
	 *
	 * @param s The input string.
	 * @return The string with variables resolved, or the same string if it doesn't contain any variables to resolve.
	 */
	public String resolve(String s) {
		return createSession(null).resolve(s);
	}

	/**
	 * Resolve variables in the specified string and sends the results to the specified writer.
	 *
	 * 
	 * This is a shortcut for calling createSession(null).resolveTo(s, w);.
	 * 
This method can only be used if the string doesn't contain variables that rely on the existence of session
	 * variables.
	 *
	 * @param s The input string.
	 * @param w The writer to send the result to.
	 * @throws IOException
	 */
	public void resolveTo(String s, Writer w) throws IOException {
		createSession(null).resolveTo(s, w);
	}
}