#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#define SCREEN_WIDTH    128
#define SCREEN_HEIGHT    64
#define TEXT_1_WIDTH     21
#define TEXT_1_HEIGHT     8
#define OLED_RESET       -1
#define SCREEN_ADDRESS 0x3C
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

int buttonPin[] = {2, 3, 4, 5, 7, 8}; // button array
const int buttons = sizeof(buttonPin) / sizeof(buttonPin[0]); // number of buttons
unsigned long timer[buttons], timeout[buttons]; // debounce array
bool currentButtonState[buttons], lastButtonRead[buttons], currentButtonRead[buttons]; // state array
int buttonCount[buttons];

void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS);
  display.clearDisplay(); // clear OLED buffer
  display.display(); // show cleared buffer

  for (int i = 0; i < buttons; i++) { // configure buttons
    pinMode(buttonPin[i], INPUT_PULLUP); // pin to button (n.o.), button to gnd
    timeout[i] = 50; // debounce timeout
  }

  oledText();
  delay(1000);
  oledBox();
  delay(1000);
  display.clearDisplay();
  display.setCursor((128 - 13 * 6) / 2, (64 - 5) / 2); // center/middle text
  display.print("Press a button.");
  display.display();
}

int thebutton;

void loop() {
  for (int i = 0; i < buttons; i++) {
    readButton(i);
  }
  if (thebutton) {
    Serial.print(thebutton);
    thebutton = 0;
  }
}

void readButton(int readPin) {
  currentButtonRead[readPin] = digitalRead(buttonPin[readPin]); // read button pin

  if (currentButtonRead[readPin] != lastButtonRead[readPin]) { // if button pin changes...
    timer[readPin] = millis(); // ...start a timer
    lastButtonRead[readPin] = currentButtonRead[readPin]; // ... and store current state
  }

  if ((millis() - timer[readPin]) > timeout[readPin]) { // if button change was longer than debounce timeout
    if (currentButtonState[readPin] == HIGH && lastButtonRead[readPin] == LOW) {  // ... and State is "NOT pressed" while Button "IS PRESSED"
      //==================================================
      // a button was pressed, use commands or functions
      digitalWrite(LED_BUILTIN, HIGH);
      thebutton = buttonPin[readPin];
      showButton(++buttonCount[readPin]); // Count the button[pin]
      digitalWrite(LED_BUILTIN, LOW);
      //==================================================
    }
    currentButtonState[readPin] = currentButtonRead[readPin]; // update button state
  }
}

void showButton(unsigned long count) {
  Serial.print("Button (count): ");
  for (int i = 0; i < buttons; i++) {
    Serial.print(buttonPin[i]);  // pin number
    Serial.print("(");
    Serial.print(buttonCount[i]);   // button presses
    Serial.print(") ");
  }
  Serial.println();
}

void oledBox() {
  display.drawRect(0, 0, SCREEN_WIDTH - 1, SCREEN_HEIGHT - 1, WHITE);
  display.display();
}

void oledText() {
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 0);

  for (int j = 0; j < TEXT_1_HEIGHT; j++) {
    for (int i = 0; i < TEXT_1_WIDTH; i++) {
      display.print("X");
    }
    display.println();
  }
  display.display();
}