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

#define SCREEN_WIDTH 128 
#define SCREEN_HEIGHT 64 
#define rowNum  4 // four row
#define colNum  4 // four columns

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

int keyIndex;

unsigned long lastClick[rowNum][colNum] = {
  {0, 0, 0, 0},   
  {0, 0, 0, 0},  
  {0, 0, 0, 0}, 
  {0, 0, 0, 0}  
};

char keys[rowNum][colNum] = {
  {'1', '2', '3', ' '},   //
  {'4', '5', '6', '~'},   //backspace   udh
  {'7', '8', '9', '^'},   //capslock    udh
  {'*', '0', '#', '\n'}    //enter       
};

char keys1[rowNum][colNum] = {
  {'1', 'a', 'd', ' '}, 
  {'g', 'j', 'm', '~'},  
  {'p', 't', 'w', '^'},
  {'*', '0', '#', '\n'}
};

char keys2[rowNum][colNum] = {
  {'1', 'b', 'e', ' '}, 
  {'h', 'k', 'n', '~'},  
  {'q', 'u', 'x', '^'},
  {'*', '0', '#', '\n'} 
};

char keys3[rowNum][colNum] = {
  {'1', 'c', 'f', ' '}, 
  {'i', 'l', 'o', '~'},  
  {'r', 'v', 'y', '^'},
  {'*', '0', '#', '\n'}   
};

int pinState = 0;
int lastFlicker = LOW;
int lastState = LOW;
bool capsLock = 0;

String sentence;
char rowPins[rowNum] = {19, 18, 5, 17}; 
char colPins[colNum] = {16, 4, 12, 15};   

void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.display();

  for(char r = 0; r < rowNum; r++){
    pinMode(rowPins[r], OUTPUT);   
    digitalWrite(rowPins[r], HIGH);  
  }

  for(char c = 0; c < colNum; c++){
    pinMode(colPins[c], INPUT_PULLUP);
  }
}

void loop() {
  char key;
  key = getKey();
  if (key == '~') {
    int l = sentence.length();
    sentence.remove(l-1,1);
    display.clearDisplay();
  }
  else if (key == '^') {
    capsLock = !capsLock;
  }
  else if (key != '?') {
    if (capsLock) {
      key = toupper(key);
    }
    sentence += key;
    display.clearDisplay();
  }
  
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 10);
  display.println(sentence);
  display.display();
}

// DITAHAN GA MUNCUL TERUSSSS TP BLM DEBOUNCE
char getKey() {
  char key = '?';
  for (char r = 0; r < rowNum; r++) {
    digitalWrite(rowPins[r], LOW);

    for (char c = 0; c < colNum; c++) {
      if (digitalRead(colPins[c]) == LOW) {
        delay(50);
        while (digitalRead(colPins[c]) == LOW) {
          pinState = digitalRead(colPins[c]);

          if ((pinState == LOW) && (lastState == HIGH)) {     // kalau tertekan
          
            if (((millis() - lastClick[r][c]) < 800) && (r < (rowNum-1)) && (c < (colNum-1))) {   // kalo tombol yg sama ditekan lagi
              if (keyIndex == 0) {
                keyIndex++;
                key = keys1[r][c];
              } else if (keyIndex == 1) {
                keyIndex++;
                key = keys2[r][c];
              } else if (keyIndex == 2) {
                keyIndex++;
                key = keys3[r][c];
              } else if (keyIndex == 3) {
                if ((r == 2) && (c == 0)) {      // pqrs
                  key = 's';
                  keyIndex++;
                } else if ((r == 2) && (c == 2)) {    // wxyz
                  key = 'z';
                  keyIndex++;
                } else {
                  keyIndex = 0;
                  key = keys[r][c];
                }  
              } else if (keyIndex == 4) {     // khusus abis s dan z
                keyIndex = 0;
                key = keys[r][c];
              }

              int l = sentence.length();
              sentence.remove(l-1,1);       // hapus char sebelumnya supaya bisa direplace

            } else {
              key = keys[r][c];
              keyIndex = 0;
            }
            
            lastClick[r][c] = millis();
            lastState = pinState;
          }
        }
      }
      lastState = HIGH;
    }
    digitalWrite(rowPins[r], HIGH);
  }
  return key;
}