// Board: Adafruit Feather M0

#include <Arduino.h>

#include <Adafruit_GFX.h>
#include "Adafruit_LEDBackpack.h"  // "Adafruit LED Backpack Library" v1.5.0

#define MEASUREMENT_PERIOD_MS 100
#define PULSES_PER_REVOLUTION 8

Adafruit_7segment matrix = Adafruit_7segment();

// --- Tachometer variables ---
const int TACH_INTERRUPT_PIN = A0; // Or any other digital pin capable of interrupts
volatile unsigned long g_isr_pulse_count_total = 0; // ISR increments this continuously
unsigned long g_main_last_pulse_count_snapshot = 0; // Main loop stores previous snapshot here
unsigned long last_measurement_time = 0;

// --- Interrupt Service Routine (ISR) ---
void count_pulse() {
  g_isr_pulse_count_total++;
}

void show(int num) {
	matrix.print(num, DEC);
	matrix.writeDisplay();
}

void setup() {
	matrix.begin(0x70);

	Serial.begin(115200);
	// Serial.setDebugOutput(true);

  // --- Setup Tachometer Interrupt ---
  pinMode(TACH_INTERRUPT_PIN, INPUT_PULLUP); // Set pin as input with internal pull-up resistor
  attachInterrupt(digitalPinToInterrupt(TACH_INTERRUPT_PIN), count_pulse, RISING);

	delay(1000);

	Serial.println();
	Serial.println();
	Serial.println("================");
	Serial.println("BOOT UP");

	show(99999);

}

void loop() {
  unsigned long current_time = millis();

  if (current_time - last_measurement_time >= MEASUREMENT_PERIOD_MS) {
    unsigned long current_total_snapshot;

    // Atomically read the total pulse count
    noInterrupts();
    current_total_snapshot = g_isr_pulse_count_total;
    interrupts();

    // Calculate pulses collected during this interval
    unsigned long collected_pulses = current_total_snapshot - g_main_last_pulse_count_snapshot;
    
    // Store the current total snapshot for the next interval's calculation
    g_main_last_pulse_count_snapshot = current_total_snapshot;

    unsigned long actual_elapsed_time = current_time - last_measurement_time;

    // Calculate RPM
    // RPM = (pulses / pulses_per_revolution) / (actual_elapsed_time_ms / 1000 / 60)
    // RPM = (pulses / pulses_per_revolution) * (60000 / actual_elapsed_time_ms)
    // Ensure floating point division for accuracy before converting to int for display
    float rpm_float = 0.0;
    if (actual_elapsed_time > 0) { // Avoid division by zero
        rpm_float = ( (float)collected_pulses / PULSES_PER_REVOLUTION ) * (60000.0 / actual_elapsed_time);
    }
    int rpm = (int)rpm_float;

    show(rpm);

    // Debugging output
    Serial.print("Pulses: "); Serial.print(collected_pulses);
    Serial.print("\tElapsed ms: "); Serial.print(actual_elapsed_time);
    Serial.print("\tRPM: "); Serial.println(rpm);

    last_measurement_time = current_time;
  }
}