/*
 * Calculate braking distances.
 *
 * $Id: braking.c,v 1.4 2009/01/04 01:04:07 grog Exp $
 */

#include <ctype.h>
#include <errno.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

void usage (char *me)
{
  fprintf (stderr,
           "Usage:\n"
           "%s speed reaction deceleration [sample-distance]\n"
           "\tspeed is initial speed in km/h\n"
           "\treaction is reaction time in seconds\n"
           "\tdeceleration is braking deceleration in m/sē\n"
           "\tsample-distance is the distance for which to calculate the residual speed\n",
           me );
  exit (1);
}

int main (int argc, char *argv [])
{
  int verbose = 0;
  int arg;
  float speed;
  float reaction_time;
  float reaction_distance;
  float deceleration;
  float deceleration_time;
  float deceleration_distance;
  float total_time;
  float total_distance;
  float sample_distance;                        /* distance to sample speed */
  float sample_speed;                           /* and speed at that time */

  if (argc < 4)
    usage (argv [0]);
  if (! strcmp (argv [1], "-v"))
  {
    verbose = 1;
    arg = 2;
  }
  else
    arg = 1;
  speed = atof (argv [arg++]) / 3.6;            /* in m/s */
  reaction_time = atof (argv [arg++]);          /* seconds */
  deceleration = atof (argv [arg++]);           /* m/sē */
  deceleration_time = speed / deceleration;     /* time to decelerate to 0 */
  reaction_distance = speed * reaction_time;
  deceleration_distance = speed * deceleration_time / 2; /* because average speed is half */
  total_time = reaction_time + deceleration_time;
  total_distance = reaction_distance + deceleration_distance;
  if (argc > arg)                               /* specify speed at given distance */
  {
    sample_distance = atof (argv [arg++]);
    if (sample_distance >= total_distance)
      sample_speed = 0.0;
    else if (sample_distance <= reaction_distance)
      sample_speed = speed;
    else
      sample_speed = speed * sqrt ((total_distance - sample_distance) / deceleration_distance);
    if (verbose)
      printf ("Speed\tSpeed\tReact\tReact\tDecel\tDecel\tTotal\tTotal\tSample\tSample\tSample\n"
              "(km/h)\t(m/s)\tTime\tDist\tTime\tDistance Time\tDistance Dist\tSpeed\tSpeed\n"
              "\t\t\t\t\t\t\t\t\t(km/h)\t(m/s)\n");
    printf ("%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\n",
            speed * 3.6,
            speed,
            reaction_time,
            reaction_distance,
            deceleration_time,
            deceleration_distance,
            total_time,
            total_distance,
            sample_distance,
            sample_speed * 3.6,
            sample_speed);                      /* in km/h */
  }
  else
  {
    if (verbose)
      printf ("Speed\tSpeed\tReact\tReact\tDecel\tDecel\tTotal\tTotal\n"
              "(km/h)\t(m/s)\tTime\tDist\tTime\tDistance Time\tDistance\n");
    printf ("%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\t%6.2f\n",
            speed * 3.6,
            speed,
            reaction_time,
            reaction_distance,
            deceleration_time,
            deceleration_distance,
            total_time,
            total_distance );
  }
  return 0;
}