/*
 * Copyright (c) 2020 Alibaba Group Holding Limited. All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation. Alibaba designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <jvmti.h>

void Jvmti_Error(int errcode, const char *msg) {
  if (errcode != JVMTI_ERROR_NONE) {
    printf("%s, error code: [%d]\n", errcode, msg);
    exit(1);
  }
}

#define JVMTI_CHECK(x, str) (Jvmti_Error(x, str))

void JNICALL
SingleStepCallBack(jvmtiEnv *jvmti_env,
                   JNIEnv* jni_env,
                   jthread thread,
                   jmethodID method,
                   jlocation location)
{
}

JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {

  // 1. get the jvmti env
  jvmtiEnv *jvmti = NULL;
  JVMTI_CHECK((*jvm)->GetEnv(jvm, (void **)&jvmti, JVMTI_VERSION_1), "env get error");

  // 2. grant the ability to the jvmti: can single step
  jvmtiCapabilities noryoku;
  memset((void *)&noryoku, 0, sizeof(jvmtiCapabilities));
  noryoku.can_generate_single_step_events = 1;
  JVMTI_CHECK((*jvmti)->AddCapabilities(jvmti, &noryoku), "add capability error");

  // 3. set: every single step, we can get a notification.
  JVMTI_CHECK((*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_SINGLE_STEP, NULL), "set notification failed");

  // 4. when a notification happens, we will get a callback! This callback will booooom.
  jvmtiEventCallbacks callbacks;
  memset((void *)&callbacks, 0, sizeof(callbacks));
  callbacks.SingleStep = &SingleStepCallBack;
  JVMTI_CHECK((*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks)), "set callback failed");

  return 0;
}