/*
 * 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
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "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 ext.test4j.apache.commons.lang.text;

import java.util.Map;

/**
 * Lookup a String key to a String value.
 * <p>
 * This class represents the simplest form of a string to string map. It has a
 * benefit over a map in that it can create the result on demand based on the
 * key.
 * <p>
 * This class comes complete with various factory methods. If these do not
 * suffice, you can subclass and implement your own matcher.
 * <p>
 * For example, it would be possible to implement a lookup that used the key as
 * a primary key, and looked up the value on demand from the database
 * 
 * @author Apache Software Foundation
 * @since 2.2
 * @version $Id: StrLookup.java 905636 2010-02-02 14:03:32Z niallp $
 */
@SuppressWarnings("rawtypes")
public abstract class StrLookup {

	/**
	 * Lookup that always returns null.
	 */
	private static final StrLookup NONE_LOOKUP;
	/**
	 * Lookup that uses System properties.
	 */
	private static final StrLookup SYSTEM_PROPERTIES_LOOKUP;
	static {
		NONE_LOOKUP = new MapStrLookup(null);
		StrLookup lookup = null;
		try {
			lookup = new MapStrLookup(System.getProperties());
		} catch (SecurityException ex) {
			lookup = NONE_LOOKUP;
		}
		SYSTEM_PROPERTIES_LOOKUP = lookup;
	}

	// -----------------------------------------------------------------------
	/**
	 * Returns a lookup which always returns null.
	 * 
	 * @return a lookup that always returns null, not null
	 */
	public static StrLookup noneLookup() {
		return NONE_LOOKUP;
	}

	/**
	 * Returns a lookup which uses {@link System#getProperties() System
	 * properties} to lookup the key to value.
	 * <p>
	 * If a security manager blocked access to system properties, then null will
	 * be returned from every lookup.
	 * <p>
	 * If a null key is used, this lookup will throw a NullPointerException.
	 * 
	 * @return a lookup using system properties, not null
	 */
	public static StrLookup systemPropertiesLookup() {
		return SYSTEM_PROPERTIES_LOOKUP;
	}

	/**
	 * Returns a lookup which looks up values using a map.
	 * <p>
	 * If the map is null, then null will be returned from every lookup. The map
	 * result object is converted to a string using toString().
	 * 
	 * @param map
	 *            the map of keys to values, may be null
	 * @return a lookup using the map, not null
	 */

	public static StrLookup mapLookup(Map map) {
		return new MapStrLookup(map);
	}

	// -----------------------------------------------------------------------
	/**
	 * Constructor.
	 */
	protected StrLookup() {
		super();
	}

	/**
	 * Looks up a String key to a String value.
	 * <p>
	 * The internal implementation may use any mechanism to return the value.
	 * The simplest implementation is to use a Map. However, virtually any
	 * implementation is possible.
	 * <p>
	 * For example, it would be possible to implement a lookup that used the key
	 * as a primary key, and looked up the value on demand from the database Or,
	 * a numeric based implementation could be created that treats the key as an
	 * integer, increments the value and return the result as a string -
	 * converting 1 to 2, 15 to 16 etc.
	 * <p>
	 * The {@link #lookup(String)} method always returns a String, regardless of
	 * the underlying data, by converting it as necessary. For example:
	 * 
	 * <pre>
	 * Map map = new HashMap();
	 * map.put("number", new Integer(2));
	 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
	 * </pre>
	 * 
	 * @param key
	 *            the key to be looked up, may be null
	 * @return the matching value, null if no match
	 */
	public abstract String lookup(String key);

	// -----------------------------------------------------------------------
	/**
	 * Lookup implementation that uses a Map.
	 */
	static class MapStrLookup extends StrLookup {

		/** Map keys are variable names and value. */
		private final Map map;

		/**
		 * Creates a new instance backed by a Map.
		 * 
		 * @param map
		 *            the map of keys to values, may be null
		 */
		MapStrLookup(Map map) {
			this.map = map;
		}

		/**
		 * Looks up a String key to a String value using the map.
		 * <p>
		 * If the map is null, then null is returned. The map result object is
		 * converted to a string using toString().
		 * 
		 * @param key
		 *            the key to be looked up, may be null
		 * @return the matching value, null if no match
		 */
		public String lookup(String key) {
			if (map == null) {
				return null;
			}
			Object obj = map.get(key);
			if (obj == null) {
				return null;
			}
			return obj.toString();
		}
	}
}