// https://forum.arduino.cc/t/measuring-pulse-period/994640

// board: arduino nano every
// registers emulation: none

#include <util/atomic.h>
#include <SPI.h>

//#include <Adafruit_GFX.h>
//#include <Adafruit_PCD8544.h>

// magic number
// a: 945 inch hundredths per pulse
// b: 3600000000 microseconds in an hour
// c: 6336000 inch hundredths in a mile
const float magic_number_vd = 0.000149148; // a / c
const uint32_t magic_number_vs = 536931; // a * b / c

// vehicle speed sensor
#define VSS_PIN 2
volatile uint32_t vss_time_prev_volatile = 0;
volatile uint32_t vss_period_volatile = 0;
volatile uint32_t vss_count_volatile = 0;

/* display
#define DISPLAY_DC_PIN 5 // data/command select
#define DISPLAY_CS_PIN 4 // chip select
#define DISPLAY_RST_PIN 3 // reset
Adafruit_PCD8544 display = Adafruit_PCD8544(DISPLAY_DC_PIN, DISPLAY_CS_PIN, DISPLAY_RST_PIN);
*/

// update interval
const uint32_t update_interval = 1000000UL; // microseconds
uint32_t update_time = -1;

void setup()
{
  // vss initialization
  pinMode(VSS_PIN, INPUT);
  attachInterrupt(digitalPinToInterrupt(VSS_PIN), vss_isr, RISING);

# define toneOut 8
  pinMode(toneOut, OUTPUT);

/* display initialization
  display.begin();
  display.clearDisplay();
  display.setContrast(75);
  display.setRotation(0);
*/
  delay(200); // life too short!

  Serial.begin(9600); Serial.println("bike thin just no LCD\n");
  Serial.println(magic_number_vd, 10);
  Serial.println(magic_number_vs);

// artificial periodic pulse input
  tone(8, 50);
}

void loop()
{
  uint32_t time_us = micros();
  if (time_us - update_time >= update_interval)
  {
    update_time += update_interval;
  }
  else
  {
    return;
  }
  
  uint32_t vss_time_prev;
  uint32_t vss_period;
  uint32_t vss_count;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
  {
    vss_time_prev = vss_time_prev_volatile;
    vss_period = vss_period_volatile;
    vss_count = vss_count_volatile;
  }

Serial.print(" prev: : "); Serial.print(vss_time_prev);
Serial.print(" period: "); Serial.print(vss_period);
Serial.print(" count: "); Serial.print(vss_count);




  // vehicle distance
  float vehicle_distance = vss_count * magic_number_vd;
  Serial.print(" distance "); Serial.print(vehicle_distance);

   // vehicle speed
  uint8_t vehicle_speed = 0;
  if (time_us - vss_time_prev < magic_number_vs) {
    vehicle_speed = magic_number_vs / vss_period;
    Serial.print(" calculcated speed ");
    Serial.println(vehicle_speed);
  }
  else Serial.println(" -- ");

/*
  // vehicle distance
  float vehicle_distance = vss_count * magic_number_vd;
  display.setTextSize(2);
  display.setCursor(0,24);
  if (vehicle_distance < 10) display.print("000");
  if (vehicle_distance < 100) display.print("00");
  if (vehicle_distance < 1000) display.print("0");
  display.print(vehicle_distance, 2);

  // vehicle speed
  uint8_t vehicle_speed = 0;
  if (time_us - vss_time_prev < magic_number_vs)
  {
    vehicle_speed = magic_number_vs / vss_period;
  }
  display.setTextSize(3);
  display.setCursor(0,0);
  if (vehicle_speed == 0 || vehicle_speed > 99)
  {
    display.print("--");
  }
  else
  {
    if (vehicle_speed < 10) display.print("0");
    display.print(vehicle_speed);
  }

  // write to display
  display.display();
*/
}

void vss_isr()
{
  uint32_t time_us = micros();
  vss_period_volatile = time_us - vss_time_prev_volatile;
  vss_time_prev_volatile = time_us;
  vss_count_volatile++;
}