/*
 * 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 freemarker.ext.jython;

import org.python.core.PySystemState;

import freemarker.template.utility.StringUtil;

Holds the JythonVersionAdapter so that it's only initialized when this class is accessed. This utilizes that the JVM is required to initialize the fields of a class not earlier than the class is first accessed. Furthermore, it utilizes that the JVM guarantees that the objects created as part of the class initialization will be visible with their after-initialization state for the threads that access it. /**
 * Holds the {@link JythonVersionAdapter} so that it's only initialized when this class is accessed.
 * This utilizes that the JVM is required to initialize the fields of a class not earlier than the class is
 * first accessed. Furthermore, it utilizes that the JVM guarantees that the objects created as part of the class
 * initialization will be visible with their after-initialization state for the threads that access it. 
 */
class JythonVersionAdapterHolder {
    
    final static JythonVersionAdapter INSTANCE;
    static {
        // Note: Only the textual version number is available in Jython 2.0. 
        int version;
        try {
            // Although PySystemState.version is present in all versions,
            // its type changes, so we must use reflection to get it.
            version = StringUtil.versionStringToInt(
                    PySystemState.class.getField("version").get(null).toString());
        } catch (Exception e) {
            throw new RuntimeException("Failed to get Jython version: " + e);
        }
        ClassLoader cl = JythonVersionAdapter.class.getClassLoader();
        try {
            if (version >= 2005000) {
                INSTANCE = (JythonVersionAdapter) cl.loadClass(
                        "freemarker.ext.jython._Jython25VersionAdapter")
                    .newInstance();
            } else if (version >= 2002000) {
                INSTANCE = (JythonVersionAdapter) cl.loadClass(
                        "freemarker.ext.jython._Jython22VersionAdapter")
                    .newInstance();
            } else {
                INSTANCE = (JythonVersionAdapter) cl.loadClass(
                        "freemarker.ext.jython._Jython20And21VersionAdapter")
                    .newInstance();
            }
        } catch (ClassNotFoundException e) {
            throw adapterCreationException(e);
        } catch (IllegalAccessException e) {
            throw adapterCreationException(e);
        } catch (InstantiationException e) {
            throw adapterCreationException(e);
        }
    }

    private static RuntimeException adapterCreationException(Exception e) {
        return new RuntimeException("Unexpected exception when creating JythonVersionAdapter", e);
    }

}