/* Include lib */
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>

/* Define */
#define MAX_LOOP    100

/* API generate positive random float number */
/* NOTE: not care a > b & vice versa */
double positive_float_rand_in_range(double pos_a, double pos_b)
{
  double pos_start, pos_end, float_rand;

  /* FIXME: Check wrong input a, b */

  /* Random number with in [start, end] */
  if (pos_a >= pos_b) {
    pos_start = pos_b;
    pos_end = pos_a;
  } else {
    pos_start = pos_a;
    pos_end = pos_b;
  }

  /* 
   * Random float in [a, b] = a + random float in [0, b - a], with c = b - a.
   * Random float in [0, c] = c * random float in [0, 1].
   * Random float in [0, 1] = random int / RAND_MAX
   */
  float_rand = pos_start + (pos_end - pos_start) * ((double)rand() / RAND_MAX);

  return float_rand;
}

/* API generate random float number (positive or negative) */
/* NOTE: not care a > b & vice versa */
double float_rand_in_range(double a, double b)
{
  /* Process input to generate random float in positive range, then process output */
  if (a < 0 && b < 0) {
    return -positive_float_rand_in_range(-a, -b);
  } else if (a < 0 && b > 0) {
    /* Random float in [-x, y] = random float in [0, y + x] - x, with x positive */
    return positive_float_rand_in_range(-a, b) - (-a);
  } else {  /* a > 0 && b > 0 */
    return positive_float_rand_in_range(a, b);
  }
}

/* Main func interract with user */
int main(void)
{
  int sel, i;
  double a, b;

  while (1) {
    printf("\n\nSelection:\n");
    printf("0 : Input range to generate random float\n");
    printf("1 : Exit\n");
    printf("Select: ");
    scanf("%d", &sel);

    switch (sel) {
    case 0:
      printf("Input a: ");
      scanf("%lf", &a);
      printf("Input b: ");
      scanf("%lf", &b);
      
      for (i = 0; i < MAX_LOOP; i++)
        printf("=> Random: %lf\n", positive_float_rand_in_range(a, b));
      break;
    case 1:
      return 0;
    default:
      printf("Option not available\n");
      break;
    }
  }

  return -1;
}