package org.codehaus.plexus.interpolation;

/*
 * Copyright 2007 The Codehaus Foundation.
 *
 * Licensed 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.
 */

import org.codehaus.plexus.interpolation.os.OperatingSystemUtils;

import java.io.IOException;
import java.util.Properties;

ValueSource which resolves expressions against the environment variables available from the underlying operating system (and possibly, the shell environment that created the present Java process). If the expression starts with 'env.', this prefix is trimmed before resolving the rest as an environment variable name. /**
 * {@link ValueSource} which resolves expressions against the environment variables
 * available from the underlying operating system (and possibly, the shell environment
 * that created the present Java process). If the expression starts with 'env.',
 * this prefix is trimmed before resolving the rest as an environment variable name.
 */
public class EnvarBasedValueSource
    extends AbstractValueSource
{

    private static Properties envarsCaseSensitive;
    private static Properties envarsCaseInsensitive;

    private final Properties envars;
    private final boolean caseSensitive;

    
Create a new value source for interpolation based on shell environment variables. In this
case, envar keys ARE CASE SENSITIVE.
Throws:
IOException – in case of an error./**
     * Create a new value source for interpolation based on shell environment variables. In this
     * case, envar keys ARE CASE SENSITIVE.
     *
     * @throws IOException in case of an error.
     */
    public EnvarBasedValueSource() throws IOException
    {
        this( true );
    }

    
Create a new value source for interpolation based on shell environment variables.
Params:
caseSensitive – Whether the environment variable key should be treated in a
                     case-sensitive manner for lookups
Throws:
IOException – in case of an error./**
     * Create a new value source for interpolation based on shell environment variables.
     *
     * @param caseSensitive Whether the environment variable key should be treated in a
     *                      case-sensitive manner for lookups
     * @throws IOException in case of an error.
     */
    public EnvarBasedValueSource( boolean caseSensitive ) throws IOException
    {
        super( false );
        this.caseSensitive = caseSensitive;
        this.envars = getEnvars( caseSensitive );
    }

    private static synchronized Properties getEnvars( boolean caseSensitive )
        throws IOException
    {
        if ( caseSensitive )
        {
            if ( envarsCaseSensitive == null )
            {
                envarsCaseSensitive = OperatingSystemUtils.getSystemEnvVars( caseSensitive );
            }
            return envarsCaseSensitive;
        }
        else
        {
            if ( envarsCaseInsensitive == null )
            {
                envarsCaseInsensitive = OperatingSystemUtils.getSystemEnvVars( caseSensitive );
            }
            return envarsCaseInsensitive;
        }
    }

    
If the expression starts with 'env.' then trim this prefix. Next, resolve the (possibly trimmed) expression as an environment variable name against the collection of environment variables that were read from the operating system when this ValueSource instance was created. 
Params:
expression – envar expression, like 'HOME' or 'env.HOME'
Returns:
the environment variable value for the given expression/**
     * If the expression starts with 'env.' then trim this prefix. Next, resolve
     * the (possibly trimmed) expression as an environment variable name against
     * the collection of environment variables that were read from the operating
     * system when this {@link ValueSource} instance was created.
     *
     * @param expression envar expression, like 'HOME' or 'env.HOME'
     * @return the environment variable value for the given expression
     */
    public Object getValue( String expression )
    {
        String expr = expression;

        if ( expr.startsWith( "env." ) )
        {
            expr = expr.substring( "env.".length() );
        }

        if ( !caseSensitive )
        {
            expr = expr.toUpperCase();
        }

        return envars.getProperty( expr );
    }
 
    
reset static variables acting as a cache for testing purposes only
/**
     * reset static variables acting as a cache for testing purposes only
     */
    static void resetStatics()
    {
        envarsCaseSensitive = null;
        envarsCaseInsensitive = null;
    }

}