#include <Arduino.h>
#include <U8g2lib.h>
#include <SPI.h>
#include <Wire.h>

// Create U8G2 object for the OLED display
U8G2_SSD1306_128X64_NONAME_F_SW_I2C u8g2(U8G2_R0, /* clock=*/ SCL, /* data=*/ SDA, /* reset=*/ U8X8_PIN_NONE);

unsigned long rpmtime;
float rpmfloat;
unsigned int rpm;
bool tooslow = 1;

void setup() {
  u8g2.begin();
  u8g2.setFont(u8g2_font_profont29_tf);
  TCCR1A = 0;
  TCCR1B = 0;
  TCCR1B |= (1 << CS12); // Prescaler 256
  TIMSK1 |= (1 << TOIE1); // Enable timer overflow
  pinMode(2, INPUT);
  attachInterrupt(digitalPinToInterrupt(2), RPM, FALLING); // Use digitalPinToInterrupt for compatibility
}

ISR(TIMER1_OVF_vect) {
  tooslow = 1;
}

void loop() {
  delay(1000);
  if (tooslow == 1) {
    u8g2.clearBuffer();
    u8g2.drawStr(1, 32, "SLOW!");
    u8g2.sendBuffer();
  } else {
    if (rpmtime > 0) {
      rpmfloat = 120.0 / (rpmtime / 31250.0);
      rpm = round(rpmfloat);
    } else {
      rpm = 0;
    }

    u8g2.clearBuffer();
    u8g2.setFontMode(1);
    u8g2.setBitmapMode(1);
    u8g2.drawFrame(2, 1, 124, 62);
    u8g2.setDrawColor(2);
    u8g2.setFont(u8g2_font_timR18_tr);
    u8g2.drawStr(5, 24, "Cadence");
    u8g2.setFont(u8g2_font_profont17_tr);
    u8g2.drawStr(96, 22, "rpm");
    u8g2.setDrawColor(1);
    u8g2.setFont(u8g2_font_timR24_tr);
    u8g2.setCursor(8, 54);
    u8g2.print(rpm);
    u8g2.drawLine(92, 9, 92, 25);
    u8g2.sendBuffer();
  }
}

void RPM() {
  rpmtime = TCNT1;
  TCNT1 = 0;
  tooslow = 0;
}