#include <stdio.h>
#include <stdlib.h>

#define CURGOV "/sys/devices/system/cpu/cpufreq/policy0/scaling_governor"
#define FREQS "/sys/devices/system/cpu/cpufreq/policy0/scaling_available_frequencies"
#define MAXSPDPATH "/sys/devices/system/cpu/cpufreq/policy0/scaling_max_freq"
#define CURTEMPPATH "/sys/devices/virtual/thermal/thermal_zone0/temp"

int comparestrings(char *a, char *b){
  int c = 0;
  while(a[c] != '\0' && b[c] != '\0'){
    if(a[c] != b[c]){
      return 1;
    }
    c++;
  }
  return 0;
}

int getfilec(FILE *file, char arr[]){
  int c, i;
  i = 0;
  while((c = fgetc(file)) != EOF){
    arr[i] = c;
    i++;
  }
  arr[i] = '\0';
  return i;
}

int powerof(int base, int exponent){
  int i, result;
  if (exponent == 0){
    return result = 1;
  }
  result = base;
  for(i = 0; i < exponent - 1; i++){
    result *= base;
  }
  return result;
}

int stringtoint(char number[], int length){
  int j, result;
  result = 0;
  j = 0;
  while(length - 1 >= 0){
    result += ((int)number[length - 1] - '0') * (powerof(10, j));
    j++;
    length--;
  }
  return result;
}

int stringlength(char string[]){
  int i = 0;
  while(string[i] != '\0'){
    i++;
  }
  return i;
}

int splitstr(char** dest, char line[], int index1, int index2){
  int offset = index1;
  while (line[index1] != ' ' && index1 < stringlength(line)){
    index1++;
  }
  char* p = malloc(sizeof (char)*index1);
  int i;
  for(i = 0; i < index1 - offset; i++){
    p[i] = line[i + offset];
  }
  p[i] = '\0';
  dest[index2] = p;
  return index1 + 1;
}

int countblanks(char line[]){
  int i = 0;
  int j = 0;
  while(line[i] != '\0'){
    if (line[i] == ' '){
      j++;
    }
    i++;
  }
  return j;
}

void newlinetonullbyte(char string[]){
  int i = 0;
  while (string[i] != '\0'){
    if (string[i] == '\n'){
      string[i] = '\0';
      break;
    }
    i++;
  }
}

int main(int argc, char** argv){
  /* check for no arguments or help */
  if (argc == 1 || comparestrings(argv[1], "-h") == 0
      || comparestrings(argv[1], "--help") == 0){
    fprintf(stderr, "usage: homemade_speedstep <max temp> <min temp>\n");
    fprintf(stderr, "       homemade_speedstep [-h | --help]\n");
    fprintf(stderr, "       -h | --help   prints out this help message\n");
    return 0;
  }
  /* check for correct ammount of arguments */
  if (argc != 3){
    fprintf(stderr, "error: wrong ammount of arguments given\n");
    fprintf(stderr, "       see homemade_speedstep --help\n");
    return 1;
  }
  /* set maxtemp and mintemp TODO: check for integer and difference */
  const int maxtemp = stringtoint(argv[1], stringlength(argv[1]));
  const int mintemp = stringtoint(argv[2], stringlength(argv[2]));
  /* try to open scaling_current_governor, exit on fail */
  FILE* govfile = fopen(CURGOV, "r");
  if (govfile == NULL){
    fprintf(stderr, "error: couldn't open scaling_current_governor\n");
    fprintf(stderr, "       check that you have support for cpufreq\n");
    fprintf(stderr, "       and the userspace governor in your kernel\n");
    fprintf(stderr, "       also check that you're running this program\n");
    fprintf(stderr, "       as root\n");
    return 2;
  }
  /* assign content of govfile to a temporary char array */
  char* gov = malloc(sizeof(char) * 20);
  getfilec(govfile, gov);
  /* check content of scaling_current_governor and exit on failure */
  if (comparestrings(gov, "userspace\n") != 0){
    fprintf(stderr, "error: userspace governor not set\n");
    /* free memory and close file */
    free(gov);
    fclose(govfile);
    return 3;
  }
  /* free memory and close file */
  free(gov);
  fclose(govfile);
  /* try to open scaling_available_frequencies, exit on fail */
  FILE *freqsfile = fopen(FREQS, "r");
  if (freqsfile == NULL){
    fprintf(stderr, "error: couldn't open scaling_available_frequencies\n");
    fprintf(stderr, "       check that you have support for cpufreq\n");
    fprintf(stderr, "       in your kernel and that the program is\n");
    fprintf(stderr, "       running as root\n");
    return 4;
  }
  /* assign content of freqsfile to a temporary char array */
  char* freqsfilec = malloc(sizeof(char) * 200);
  getfilec(freqsfile, freqsfilec);
  int stepc = countblanks(freqsfilec);
  /* create a char ** array with pointers to freq steps */
  char ** steps = malloc(sizeof(char*) * stepc);
  int index = 0;
  int i;
  for(i = 0; i < stepc; i++){
    index = splitstr(steps, freqsfilec, index, i);
  }
  /* free memory and close file */
  free(freqsfilec);
  fclose(freqsfile);
  /* try to open scaling_maximum_frequency, exit on fail */
  FILE* curmaxfile = fopen(MAXSPDPATH, "r");
  if (curmaxfile == NULL){
    fprintf(stderr, "error: couldn't open scaling_maximum_frequency\n");
    fprintf(stderr, "       check that you have support for cpufreq\n");
    fprintf(stderr, "       in your kernel and that the program is\n");
    fprintf(stderr, "       running as root\n");
    return 5;
  }
  /* assign content of curmaxfile to a temporary char array */
  char *curmaxfreq = malloc(sizeof(char) * 20);
  getfilec(curmaxfile, curmaxfreq);
  newlinetonullbyte(curmaxfreq);
  /* figure out what step we're on */
  int curstep = -1;
  for(i = 0; i < stepc; i++){
    if (comparestrings(steps[i], curmaxfreq) == 0){
      curstep = i;
      break;
    }
  }
  /* free memory and close file */
  free(curmaxfreq);
  fclose(curmaxfile);
  /* check if we didn't find our current step, exit on fail */
  if (curstep == -1){
    fprintf(stderr, "error: couldn't figure out the current frequency\n");
    fprintf(stderr, "       check that you have support for cpufreq\n");
    fprintf(stderr, "       in your kernel and that the program is\n");
    fprintf(stderr, "       running as root\n");
    return 6;
  }
  FILE* curtempfile;
  /* from here onwards an infinite while loop should start */
  while((curtempfile = fopen(CURTEMPPATH, "r")) != NULL){
    char* temperature = malloc(sizeof(char) * 8);
    getfilec(curtempfile, temperature);
    newlinetonullbyte(temperature);
    if (stringtoint(temperature, stringlength(temperature)) >= maxtemp
        && curstep < stepc - 1){
      curstep++;
      curmaxfile = fopen(MAXSPDPATH, "w");
      fprintf(curmaxfile, "%s\n", steps[curstep]);
      fclose(curmaxfile);
    }
    if (stringtoint(temperature, stringlength(temperature)) <= mintemp
        && curstep > 0){
      curstep--;
      curmaxfile = fopen(MAXSPDPATH, "w");
      fprintf(curmaxfile, "%s\n", steps[curstep]);
      fclose(curmaxfile);
    }
    free(temperature);
    fclose(curtempfile);
  }
  /* cleanup for graceful exit */
  free(steps);
  fclose(curtempfile);
  return 0;
}