// vim: ts=4 sw=4 expandtab ft=java
//
// @configure_input@
//
// Copyright (C) 2004, 2006 The University of Melbourne.
// Copyright (C) 2018 The Mercury team.
// This file is distributed under the terms specified in COPYING.LIB.
//
//
// This class exists to provide any native functionality required by the Java
// implementation.  It uses JNI to access a shared object which it searches
// for in all the directories listed in the current CLASSPATH.
//
// At the moment the only services provided are those relating to timing.
//

package jmercury.runtime;

public class Native {
    /**
     * SHARED_OBJ is the name of the shared object which contains
     * all the compiled native code.
     */
    private static final java.lang.String   SHARED_OBJ =
        "Native.@EXT_FOR_SHARED_LIB@";

    /**
     * attemptedLoad records whether or not the user has yet attempted
     * to load the shared library.
     */
    private static boolean  attemptedLoad = false;

    /**
     * available and isAvailable() are true when native functionality
     * is available. (ie SHARED_OBJ was loaded successfully)
     */
    private static boolean  available  = false;

    /**
     * isAvailable() as the side effect of attempting to load the library
     * if this has not already been done.
     */
    public static boolean isAvailable() {
        if (!attemptedLoad) {
            load_library();
        }
        return available;
    }

    static {
        load_library();
    }

    /**
     * load_library():
     *  Searches all the directories listed in the classpath,
     *  (including the directories containing each jar file) for the
     *  shared object SHARED_OBJ, and attempts to load this file if found.
     *  Also searches in the subdirectory Constants.MR_FULLARCH.
     *  Sets available to true if successful, false otherwise.
     */
    private static void load_library() {
        attemptedLoad = true;

        java.util.StringTokenizer classpath =
            new java.util.StringTokenizer(
                java.lang.System.getProperty("java.class.path"),
                java.lang.System.getProperty("path.separator")
            );

        while (classpath.hasMoreTokens()) {
            java.io.File dir;
            java.io.File entry = new java.io.File(classpath.nextToken());

            try {
                if (entry.isDirectory()) {
                    dir = entry;
                } else {
                    dir = entry.getParentFile();
                }
                if (dir == null) {
                    dir = new java.io.File("");
                }

                java.io.File match = new java.io.File(dir, SHARED_OBJ);
                if (match.exists() == false) {
                    dir = new java.io.File(dir, Constants.MR_FULLARCH);
                    match = new java.io.File(dir, SHARED_OBJ);
                }

                java.lang.System.load(match.getAbsolutePath());
                available = true;
                return;
            }
            catch (java.lang.Exception e) {
                continue;
            }
        } // while classpath.hasMoreTokens()

        return;
    } // load_library()

    /**
     * clock():
     *  Calls clock() from the <time.h> library.
     */
    public static native int clock();

    /**
     * clocks_per_sec():
     *  Returns the number of "clocks" per sec as defined by CLOCKS_PER_SEC.
     */
    public static native int clocks_per_sec();

    /**
     * times():
     *  Calls times() from the <time.h> library.  Results are returned
     *  in an int array of the form:
     *  { <return value>, utime, stime, cutime, cstime }
     *  If POSIX times are not available, <return value> will be set to -1,
     *  and the other values are undefined.
     *  Returns null if the array cannot be constructed.
     */
    public static native int[] times();

    /**
     * clk_tck():
     *  Returns the number of "clock ticks" per second as defined by
     *  sysconf(_SC_CLK_TCK). A `clock_t' value returned by 'times()'
     *  can be divided by this value to obtain a time in seconds.
     */
    public static native int clk_tck();

    /**
     * get_user_cpu_milliseconds():
     *  Native method to return the CPU time consumed by the process,
     *  in milliseconds, from an arbitrary initial time.
     */
    public static native int get_user_cpu_milliseconds();
}