#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <avr/pgmspace.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 32

String menuOption[] = {"Temperature", "Pressure", "Gas", "Humidity"};
const int menuOptionCount = 4;

const int downButtonPin = 5;
const int selectButtonPin = 6;
const int clearButtonPin = 7;

int selectedOption = 0;

// BUTTON PRESS STATES FOR EACH FUNCTION, ALL SET TO "LOW".
// MAKE THESE "BOOLEAN" VARIABLES AS THESE ONLY WILL BE "HIGH" OR "LOW".
boolean buttonStateDown = LOW;
boolean lastButtonStateDown = LOW;
boolean currentButtonStateDown = LOW;

// DEBOUNCE VARIABLES TO MEASURE THE DEBOUNCING TIME OF A BUTTON PUSH.
// MAKE THESE "UNSIGNED LONG" VARIABLES AS THE NUMERICAL VALUE WILL HAVE AN EXTENDED SIZE.
unsigned long lastDebounceTime = 0; // takes snapshot of time when button is pressed
unsigned long debounceDelay = 200; // delay time in milliseconds

// Setup the LCD, whatever is connected to the Arduino
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

void setup() {
  // Setup the LCD, turn on and clear
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.display();
  delay(2000);
  display.clearDisplay();

  // Set button pins as inputs
  pinMode(downButtonPin, INPUT);
  pinMode(selectButtonPin, INPUT);
  pinMode(clearButtonPin, INPUT);

  delay(1000);
}

void loop() {
  // Display the menu and handle button presses
  displayMenu();
  handleButtons();
  delay(2000);
}

void displayMenu() {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(0.5);

  for (int i = 0; i < menuOptionCount; i++) {
    display.setCursor(0, i * 8);
    display.print(menuOption[i]);
  }

  display.drawTriangle(120, selectedOption * 8, 120, selectedOption * 8 + 5, 125, selectedOption * 8 + 2, SSD1306_WHITE);
  display.display();
}

void handleButtons() {
  currentButtonStateDown = digitalRead(downButtonPin);

  if (currentButtonStateDown != lastButtonStateDown) {
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {
    if (currentButtonStateDown == LOW) {
      selectedOption++;
      if (selectedOption >= menuOptionCount) {
        selectedOption = 0;
      }
    }
  }

  // Update last button states only when the down button is pressed
  if (currentButtonStateDown == LOW) {
    lastButtonStateDown = currentButtonStateDown;
  }
}