package com.thoughtworks.xstream.core;

import com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider;
import com.thoughtworks.xstream.converters.reflection.ReflectionProvider;

import java.security.AccessControlException;

public class JVM {

    private ReflectionProvider reflectionProvider;

    private static final float majorJavaVersion = getMajorJavaVersion(System
            .getProperty("java.version"));

    static final float DEFAULT_JAVA_VERSION = 1.3f;

    /**
     * Parses the java version system property to determine the major java
     * version, ie 1.x
     * 
     * @param javaVersion
     *            the system property 'java.version'
     * @return A float of the form 1.x
     */
    static final float getMajorJavaVersion(String javaVersion) {
        try {
            return Float.parseFloat(javaVersion.substring(0, 3));
        } catch (NumberFormatException e) {
            // Some JVMs may not conform to the x.y.z java.version format
            return DEFAULT_JAVA_VERSION;
        }
    }

    public static boolean is14() {
        return majorJavaVersion >= 1.4f;
    }

    public static boolean is15() {
        return majorJavaVersion >= 1.5f;
    }

    private static boolean isSun() {
        return System.getProperty("java.vm.vendor").indexOf("Sun") != -1;
    }

    private static boolean isApple() {
        return System.getProperty("java.vm.vendor").indexOf("Apple") != -1;
    }

    private static boolean isHPUX() {
        return System.getProperty("java.vm.vendor").indexOf(
                "Hewlett-Packard Company") != -1;
    }

    private static boolean isIBM() {
        return System.getProperty("java.vm.vendor").indexOf("IBM") != -1;
    }

    private static boolean isBlackdown() {
        return System.getProperty("java.vm.vendor").indexOf("Blackdown") != -1;
    }

    /*
     * Support for sun.misc.Unsafe and sun.reflect.ReflectionFactory is present
     * in JRockit versions R25.1.0 and later, both 1.4.2 and 5.0 (and in future
     * 6.0 builds).
     */
    private static boolean isBEAWithUnsafeSupport() {
        // This property should be "BEA Systems, Inc."
        if (System.getProperty("java.vm.vendor").indexOf("BEA") != -1) {

            /*
             * Recent 1.4.2 and 5.0 versions of JRockit have a java.vm.version
             * string starting with the "R" JVM version number, i.e.
             * "R26.2.0-38-57237-1.5.0_06-20060209..."
             */
            String vmVersion = System.getProperty("java.vm.version");
            if (vmVersion.startsWith("R")) {
                /*
                 * We *could* also check that it's R26 or later, but that is
                 * implicitly true
                 */
                return true;
            }

            /*
             * For older JRockit versions we can check java.vm.info. JRockit
             * 1.4.2 R24 -> "Native Threads, GC strategy: parallel" and JRockit
             * 5.0 R25 -> "R25.2.0-28".
             */
            String vmInfo = System.getProperty("java.vm.info");
            if (vmInfo != null) {
                // R25.1 or R25.2 supports Unsafe, other versions do not
                return (vmInfo.startsWith("R25.1") || vmInfo
                        .startsWith("R25.2"));
            }
        }
        // If non-BEA, or possibly some very old JRockit version
        return false;
    }

    public Class loadClass(String name) {
        try {
            return Class.forName(name, false, getClass().getClassLoader());
        } catch (ClassNotFoundException e) {
            return null;
        }
    }

    public synchronized ReflectionProvider bestReflectionProvider() {
        if (reflectionProvider == null) {
            try {
                if (canUseSun14ReflectionProvider()) {
                    String cls = "com.thoughtworks.xstream.converters.reflection.Sun14ReflectionProvider";
                    reflectionProvider = (ReflectionProvider) loadClass(cls)
                            .newInstance();
                } else {
                    reflectionProvider = new PureJavaReflectionProvider();
                }
            } catch (InstantiationException e) {
                reflectionProvider = new PureJavaReflectionProvider();
            } catch (IllegalAccessException e) {
                reflectionProvider = new PureJavaReflectionProvider();
            } catch (AccessControlException e) {
                // thrown when trying to access sun.misc package in Applet
                // context.
                reflectionProvider = new PureJavaReflectionProvider();
            }
        }
        return reflectionProvider;
    }

    private boolean canUseSun14ReflectionProvider() {
        return ((isSun() || isApple() || isHPUX() || isIBM() || isBlackdown() || isBEAWithUnsafeSupport())
                && is14() && loadClass("sun.misc.Unsafe") != null);
    }
}