package launcher.helper;

import java.io.File;
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URLClassLoader;
import java.nio.file.Path;
import java.util.Locale;

import com.sun.management.OperatingSystemMXBean;
import launcher.LauncherAPI;
import sun.misc.URLClassPath;

public final class JVMHelper {
    // MXBeans exports
    @LauncherAPI public static final RuntimeMXBean RUNTIME_MXBEAN = ManagementFactory.getRuntimeMXBean();
    @LauncherAPI public static final OperatingSystemMXBean OPERATING_SYSTEM_MXBEAN =
        (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();

    // System properties
    @LauncherAPI public static final OS OS_TYPE = OS.byName(OPERATING_SYSTEM_MXBEAN.getName());
    @LauncherAPI public static final String OS_VERSION = OPERATING_SYSTEM_MXBEAN.getVersion();
    @LauncherAPI public static final int OS_BITS = getCorrectOSArch();
    @LauncherAPI public static final int JVM_BITS = Integer.parseInt(System.getProperty("sun.arch.data.model"));
    @LauncherAPI public static final int RAM = getRAMAmount();

    // Public static fields
    @LauncherAPI public static final Runtime RUNTIME = Runtime.getRuntime();
    @LauncherAPI public static final URLClassLoader LOADER = (URLClassLoader) ClassLoader.getSystemClassLoader();
    @LauncherAPI public static final URLClassPath UCP = getURLClassPath();

    // Useful internal fields and constants
    private static final String JAVA_LIBRARY_PATH = "java.library.path";
    private static final Field USR_PATHS_FIELD = getUsrPathsField();
    private static final Field SYS_PATHS_FIELD = getSysPathsField();

    private JVMHelper() {
    }

    @LauncherAPI
    public static void addNativePath(Path path) {
        String stringPath = path.toString();

        // Add to library path
        String libraryPath = System.getProperty(JAVA_LIBRARY_PATH);
        if (libraryPath == null || libraryPath.isEmpty()) {
            libraryPath = stringPath;
        } else {
            libraryPath += File.pathSeparatorChar + stringPath;
        }
        System.setProperty(JAVA_LIBRARY_PATH, libraryPath);

        // Reset usrPaths and sysPaths cache
        try {
            USR_PATHS_FIELD.set(null, null);
            SYS_PATHS_FIELD.set(null, null);
        } catch (IllegalAccessException e) {
            throw new InternalError(e);
        }
    }

    @LauncherAPI
    @SuppressWarnings("CallToSystemGC")
    public static void fullGC() {
        RUNTIME.gc();
        RUNTIME.runFinalization();
        LogHelper.debug("Used heap: %d MiB", RUNTIME.totalMemory() - RUNTIME.freeMemory() >> 20);
    }

    @LauncherAPI
    public static void halt0(int status) {
        LogHelper.debug("Trying to halt JVM");
        try {
            getMethod(Class.forName("java.lang.Shutdown"), "halt0", int.class).invoke(null, status);
        } catch (ClassNotFoundException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
            throw new InternalError(e);
        }
    }

    @LauncherAPI
    public static boolean isJVMMatchesSystemArch() {
        return JVM_BITS == OS_BITS;
    }

    @LauncherAPI
    public static void verifySystemProperties(Class<?> mainClass, boolean requireSystem) {
        Locale.setDefault(Locale.US);

        // Verify class loader
        LogHelper.debug("Verifying class loader");
        if (requireSystem && !mainClass.getClassLoader().equals(LOADER)) {
            throw new SecurityException("ClassLoader should be system");
        }

        // Verify system and java architecture
        LogHelper.debug("Verifying JVM architecture");
        if (!isJVMMatchesSystemArch()) {
            LogHelper.warning("Java and OS architecture mismatch");
            LogHelper.warning("It's recommended to download %d-bit JRE", OS_BITS);
        }
    }

    @SuppressWarnings("CallToSystemGetenv")
    private static int getCorrectOSArch() {
        // As always, mustdie must die
        if (OS_TYPE == OS.MUSTDIE) {
            return System.getenv("ProgramFiles(x86)") == null ? 32 : 64;
        }

        // Or trust system property (maybe incorrect)
        return System.getProperty("os.arch").contains("64") ? 64 : 32;
    }

    private static Field getField(Class<?> clazz, String name) throws NoSuchFieldException {
        Field field = clazz.getDeclaredField(name);
        field.setAccessible(true);
        return field;
    }

    private static Method getMethod(Class<?> clazz, String name, Class<?>... params) throws NoSuchMethodException {
        Method method = clazz.getDeclaredMethod(name, params);
        method.setAccessible(true);
        return method;
    }

    private static int getRAMAmount() {
        int physicalRam = (int) (OPERATING_SYSTEM_MXBEAN.getTotalPhysicalMemorySize() >> 20);
        return Math.min(physicalRam, OS_BITS == 32 ? 1536 : 4096); // Limit 32-bit OS to 1536 MiB, and 64-bit OS to 4096 MiB (because it's enough)
    }

    private static Field getSysPathsField() {
        try {
            return getField(ClassLoader.class, "sys_paths");
        } catch (NoSuchFieldException e) {
            throw new InternalError(e);
        }
    }

    private static URLClassPath getURLClassPath() {
        try {
            return (URLClassPath) getField(URLClassLoader.class, "ucp").get(LOADER);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw new InternalError(e);
        }
    }

    private static Field getUsrPathsField() {
        try {
            return getField(ClassLoader.class, "usr_paths");
        } catch (NoSuchFieldException e) {
            throw new InternalError(e);
        }
    }

    @LauncherAPI
    public enum OS {
        MUSTDIE("mustdie"), LINUX("linux"), MACOSX("macosx");
        public final String name;

        OS(String name) {
            this.name = name;
        }

        public static OS byName(String name) {
            if (name.startsWith("Windows")) {
                return MUSTDIE;
            }
            if (name.startsWith("Linux")) {
                return LINUX;
            }
            if (name.startsWith("Mac OS X")) {
                return MACOSX;
            }
            throw new RuntimeException(String.format("This shit is not yet supported: '%s'", name));
        }
    }
}