#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Keypad.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

#define ROW_NUM     4 // four rows
#define COLUMN_NUM  4 // four columns

char keys[ROW_NUM][COLUMN_NUM] = {
  {'1','2','3', 'A'},
  {'4','5','6', 'B'},
  {'7','8','9', 'C'},
  {'*','0','#', 'D'}
};

byte pin_rows[ROW_NUM]      = {12, 14, 27, 26}; // GPIO19, GPIO18, GPIO5, GPIO17 connect to the row pins
byte pin_column[COLUMN_NUM] = {25, 33, 32, 35};   // GPIO16, GPIO4, GPIO0, GPIO2 connect to the column pins

Keypad keypad = Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );

const double pi = 3.142;

float calculateArea(float circumference) {
    float radius = circumference / (2 * pi);
    return pi * radius * radius;
}

void setup() {
  Serial.begin(9600);
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for(;;);
  }
  display.display();
  delay(2000);
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.print("Enter Circumference:");
  display.display();
}

void loop() {
  char key = keypad.getKey();
  static String inputStr = "";
  static float circumference = 0.0;

  if (key) {
    if (key == '#') {
      circumference = inputStr.toFloat();
      float area = calculateArea(circumference);
      display.clearDisplay();
      display.setCursor(0, 0);
      display.print("Circumference: ");
      display.println(circumference);
      display.print("Area: ");
      display.println(area);
      display.display();
      inputStr = "";
      circumference = 0.0;
    } else {
      inputStr += key;
      display.clearDisplay();
      display.setCursor(0, 0);
      display.print("Enter Circumference:");
      display.setCursor(0, 16);
      display.println(inputStr);
      display.display();
    }
  }
}