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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This version represents the developer version, the "bleeding edge" of development, you could say. New functionality gets added to this version.
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/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see .
 */

/*
 *    Environment.java
 *    Copyright (C) 2008-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core;

import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.TreeMap;

/**
 * This class encapsulates a map of all environment and java system properties.
 * There are methods for adding and removing variables to this Environment
 * object as well as to the system wide global environment. There is also a
 * method for replacing key names (enclosed by ${}) with their associated value
 * in Strings.
 * 
 * @author Mark Hall (mhall{[at]}pentaho{[dot]}com)
 * @version $Revision: 10203 $
 */
public class Environment implements RevisionHandler {

  private static Environment m_systemWide = new Environment();

  // Map to hold all the system environment variables + java properties
  private final Map m_envVars = new TreeMap();

  public Environment() {
    // get the env variables first
    Map env = System.getenv();
    Set keys = env.keySet();
    Iterator i = keys.iterator();
    while (i.hasNext()) {
      String kv = i.next();
      String value = env.get(kv);
      m_envVars.put(kv, value);
    }

    // get the java properties
    Properties jvmProps = System.getProperties();
    Enumeration pKeys = jvmProps.propertyNames();
    while (pKeys.hasMoreElements()) {
      String kv = (String) pKeys.nextElement();
      String value = jvmProps.getProperty(kv);
      m_envVars.put(kv, value);
    }
    m_envVars.put("weka.version", Version.VERSION);
  }

  /**
   * Get the singleton system-wide (visible to every class in the running VM)
   * set of environment variables.
   * 
   * @return the system-wide set of environment variables.
   */
  public static Environment getSystemWide() {
    return m_systemWide;
  }

  /**
   * Tests for the presence of environment variables.
   * 
   * @param source the string to test
   * @return true if the argument contains one or more environment variables
   */
  public static boolean containsEnvVariables(String source) {
    return (source.indexOf("${") >= 0);
  }

  /**
   * Substitute a variable names for their values in the given string.
   * 
   * @param source the source string to replace variables in
   * @return a String with all variable names replaced with their values
   * @throws Exception if an unknown variable name is encountered
   */
  public String substitute(String source) throws Exception {
    // Grab each variable out of the string
    int index = source.indexOf("${");

    while (index >= 0) {
      index += 2;
      int endIndex = source.indexOf('}');
      if (endIndex >= 0 && endIndex > index + 1) {
        String key = source.substring(index, endIndex);

        // look this sucker up
        String replace = m_envVars.get(key);
        if (replace != null) {
          String toReplace = "${" + key + "}";
          source = source.replace(toReplace, replace);
        } else {
          throw new Exception("[Environment] Variable " + key
            + " doesn't seem to be set.");
        }
      } else {
        break;
      }
      index = source.indexOf("${");
    }
    return source;
  }

  /**
   * Add a variable to the internal map of this properties object.
   * 
   * @param key the name of the variable
   * @param value its value
   */
  public void addVariable(String key, String value) {
    m_envVars.put(key, value);
  }

  /**
   * Add a a variable to the internal map of this properties object and to the
   * global system-wide environment;
   * 
   * @param key the name of the variable
   * @param value its value
   */
  public void addVariableSystemWide(String key, String value) {
    addVariable(key, value); // local

    // system wide
    if (this != getSystemWide()) {
      getSystemWide().addVariableSystemWide(key, value);
    }
    System.setProperty(key, value);
  }

  /**
   * Remove a named variable from the map.
   * 
   * @param key the name of the varaible to remove.
   */
  public void removeVariable(String key) {
    m_envVars.remove(key);
  }

  /**
   * Get the names of the variables (keys) stored in the internal map.
   * 
   * @return a Set of variable names (keys)
   */
  public Set getVariableNames() {
    return m_envVars.keySet();
  }

  /**
   * Get the value for a particular variable.
   * 
   * @param key the name of the variable to get
   * @return the associated value or null if this variable is not in the
   *         internal map
   */
  public String getVariableValue(String key) {
    return m_envVars.get(key);
  }

  /**
   * Main method for testing this class.
   * 
   * @param args a list of strings to replace variables in (e.g. "\${os.name}
   *          "\${java.version}")
   */
  public static void main(String[] args) {
    Environment t = new Environment();
    // String test =
    // "Here is a string with the variable ${java.version} and ${os.name} in it";

    if (args.length == 0) {
      System.err
        .println("Usage: java weka.core.Environment   ...");
    } else {
      try {
        for (String arg : args) {
          String newS = t.substitute(arg);
          System.out.println("Original string:\n" + arg + "\n\nNew string:\n"
            + newS);
        }
      } catch (Exception ex) {
        ex.printStackTrace();
      }
    }
  }

  /**
   * Returns the revision string.
   * 
   * @return the revision
   */
  @Override
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 10203 $");
  }
}