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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

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

const byte ROWS = 4;
const byte COLS = 4;

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

byte rowPins[ROWS] = {3, 4, 5, 6};
byte colPins[COLS] = {7, 8, A0, A1};

Keypad keypad = Keypad(
  makeKeymap(keys), rowPins, colPins, ROWS, COLS
);

String message = "";

void showMessage() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.println("EMERGENCY DEVICE");
  display.println("----------------");

  display.println("Message:");
  display.println(message);

  display.println();
  display.println("# = Send (demo)");
  display.println("* = Clear");

  display.display();
}

void setup() {
  Serial.begin(9600);

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED initialization failed");
    while (true) {}
  }

  showMessage();
  Serial.println("Device ready. Enter a message.");
}

void loop() {
  char key = keypad.getKey();

  if (key == NO_KEY) return;

  if (key == '*') {
    message = "";
    Serial.println("Message cleared");
  }
  else if (key == '#') {
    Serial.print("DEMO MESSAGE: ");
    Serial.println(message);
    message = "";
  }
  else if (message.length() < 60) {
    message += key;
  }

  showMessage();
}