#include <stdio.h>
#include <unistd.h>

#define LUA_LIB
#include "lua.h"
#include "lauxlib.h"

/* Show overall CPU utilization of the system 
 * This is a part of the post http://phoxis.org/2013/09/05/finding-overall-and-per-core-cpu-utilization
 */

#define BUF_MAX 1024

int 
read_fields (FILE *fp, unsigned long long int *fields) {
  int retval;
  char buffer[BUF_MAX];
  if (!fgets (buffer, BUF_MAX, fp)) {
    perror ("Error");
  }
  retval = sscanf (buffer, "cpu %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu", 
  &fields[0], 
  &fields[1], 
  &fields[2], 
  &fields[3], 
  &fields[4], 
  &fields[5], 
  &fields[6], 
  &fields[7], 
  &fields[8], 
  &fields[9]); 
  if (retval < 4) {
    fprintf (stderr, "Error reading /proc/stat cpu field\n");
    return 0;
  }
  return 1;
}

/* Immunio Lua bindings */

static int
lua_cpuload(lua_State *L) {
  FILE *fp;
  unsigned long long int fields[10], total_tick, total_tick_old, idle, idle_old, del_total_tick, del_idle;
  int i;
  double percent_usage;
  char str[100];

  fp = fopen ("/proc/stat", "r");
  if (fp == NULL) {
    perror ("Error");
  }

  if (!read_fields (fp, fields)) {
    return 0;
  }

  for (i=0, total_tick = 0; i<10; i++) {
    total_tick += fields[i];
  }
  idle = fields[3]; /* idle ticks index */
  sleep (1);
  total_tick_old = total_tick;
  idle_old = idle;
  fseek (fp, 0, SEEK_SET);
  fflush (fp);
  if (!read_fields (fp, fields)) {
    return 0;
  }

  for (i=0, total_tick = 0; i<10; i++) {
    total_tick += fields[i];
  } 
  idle = fields[3];

  del_total_tick = total_tick - total_tick_old;
  del_idle = idle - idle_old;

  percent_usage = ((del_total_tick - del_idle) / (double) del_total_tick) * 100; /* 3 is index of idle time */
  sprintf(str,"%f",percent_usage);
  lua_pushstring(L, str);
  fclose(fp);
  return 1;
}

static int
lua_stat(lua_State *L) {
  FILE *fp;
  char buf[3000];
  if ((fp=fopen("/proc/stat","r"))==NULL) {
    printf("Error! opening file");
  }
  else {
    fread(buf, 1, 3000, fp);
    size_t fsize = ftell(fp);
    buf[fsize] = '\0';
    lua_pushstring(L, buf);
  }
  fclose(fp);
  return 1;
}

static const luaL_Reg libcpuload[] = {
  {"cpuload", lua_cpuload},
  {"stat", lua_stat},
  {NULL, NULL}
};

int
luaopen_cpuload(lua_State *L) {
  luaL_checkversion(L);
  luaL_register(L, "perf", libcpuload);
  return 1;
}