#include <Wire.h>
#include <LiquidCrystal_I2C.h>


// Variables
float buttonTimer = 0;
bool buttonPressed = false;
String fullString = "";
String pressedCharacter = "";
bool stringAdded = false;
double convertedNumber = 0;

// Keypad constants
// Mapping of rows and corresponding characters
struct KeyMapping {
  byte rowValue;        // Value to write for the row
  byte cases[4];        // Possible return values from Wire.read()
  const char *chars[4]; // Corresponding characters for each case
};

KeyMapping keyMap[] = {
  {B11101111, {238, 237, 235, 231}, {"1", "2", "3", "A"}},
  {B11011111, {222, 221, 219, 215}, {"4", "5", "6", "B"}},
  {B10111111, {190, 189, 187, 183}, {"7", "8", "9", "C"}},
  {B01111111, {126, 125, 123, 119}, {"*", "0", "#", "D"}}
};

// Objects
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Wire.begin();
  Wire.setClock(400000L);
  Serial.begin(9600);
  Serial.println("PCF8574 with a keypad");

  // lcd
  lcd.init();
  lcd.setCursor(0, 0);
  lcd.print("Keypad 123-ABC");
  lcd.setCursor(0, 1);
  lcd.print("Demo");

  delay(2000);

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("String: ");
  lcd.setCursor(0, 1);
  lcd.print("Double: ");
}

void loop() {
  readKeypad();
  checkInput();

}

void checkInput() {
  if(buttonPressed) {
    if(stringAdded) {
      fullString = fullString + pressedCharacter;
      lcd.setCursor(8, 0);
      lcd.print(fullString);
      lcd.setCursor(8, 1);
      lcd.print("        ");
      stringAdded = false;
    }
  }
}

/****/
void readKeypad() {
  if (buttonPressed) {
    if (millis() - buttonTimer > 300) {
      buttonTimer = millis();
      buttonPressed = false;
    }
    return;
  }

  for (auto &row : keyMap) {
    Wire.beginTransmission(0x20);
    Wire.write(row.rowValue);
    Wire.endTransmission();

    Wire.requestFrom(0x20, 1);
    byte readValue = Wire.read();

    for (int i = 0; i < 4; i++) {
      if (readValue == row.cases[i]) {
        Serial.print(row.chars[i]);
        pressedCharacter = row.chars[i];
        buttonPressed = true;
        stringAdded = true;
        return; // Exit after finding the pressed key
      }
    }
  }
}


/** Demonstration of keypad on i2c 
void readKeypad() {
  if(buttonPressed == true) {
    if(millis() - buttonTimer > 300) {
      // The buttonPressed is only set back after 300ms so we cannot press button quickly
      buttonTimer = millis();
      buttonPressed = false;
    }
  }
  else {
    //========== First row ============//
    Wire.beginTransmission(0x20);
    Wire.write(B11101111);
    //B[P7]11101111[P0] -> [P7]1110[P4] - activates first row, [P3]1111[P0] - Sets all pins high on the MUX
    Wire.endTransmission();

    Wire.requestFrom(0x20, 1);
    switch(Wire.read()) {
      //11101110 - P0 pin went low after pressing the button 1
      case 238: // B11101110 -> D238
        Serial.print("1");
        pressedCharacter = "1";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11101101 - P1 pin went low after pressing the button 2
      case 237: // B11101101 -> D237
        Serial.print("2");
        pressedCharacter = "2";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11101011 - P2 pin went low after pressing the button 3
      case 235: // B11101011 -> D235
        Serial.print("3");
        pressedCharacter = "3";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11100111 - P3 pin went low after pressing the button A
      case 231: // B11100111 -> D231
        Serial.print("A");
        pressedCharacter = "A";
        buttonPressed = true;
        stringAdded = true;
        break;
    }


    //========== Second row ============//
    Wire.beginTransmission(0x20);
    Wire.write(B11011111);
    //B[P7]11011111[P0] -> [P7]1101[P4] - activates second row, [P3]1111[P0] - Sets all pins high on the MUX
    Wire.endTransmission();

    Wire.requestFrom(0x20, 1);
    switch(Wire.read()) {
      //11011110 - P0 pin went low after pressing the button 4
      case 222: // B11011110 -> D222
        Serial.print("4");
        pressedCharacter = "4";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11011101 - P1 pin went low after pressing the button 5
      case 221: // B11011101 -> D221
        Serial.print("5");
        pressedCharacter = "5";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11011011 - P2 pin went low after pressing the button 6
      case 219: // B11011011 -> D219
        Serial.print("6");
        pressedCharacter = "6";
        buttonPressed = true;
        stringAdded = true;
        break;

      //11010111 - P3 pin went low after pressing the button B
      case 215: // B11010111 -> D215
        Serial.print("B");
        pressedCharacter = "B";
        buttonPressed = true;
        stringAdded = true;
        break;
    }


    //========== Third row ============//
    Wire.beginTransmission(0x20);
    Wire.write(B10111111);
    //B[P7]10111111[P0] -> [P7]1011[P4] - activates second row, [P3]1111[P0] - Sets all pins high on the MUX
    Wire.endTransmission();

    Wire.requestFrom(0x20, 1);
    switch(Wire.read()) {
      //10111110 - P0 pin went low after pressing the button 7
      case 190: // B10111110 -> D190
        Serial.print("7");
        pressedCharacter = "7";
        buttonPressed = true;
        stringAdded = true;
        break;

      //10111101 - P1 pin went low after pressing the button 8
      case 189: // B10111101 -> D189
        Serial.print("8");
        pressedCharacter = "8";
        buttonPressed = true;
        stringAdded = true;
        break;

      //10111011 - P2 pin went low after pressing the button 9
      case 187: // B10111011 -> D187
        Serial.print("9");
        pressedCharacter = "9";
        buttonPressed = true;
        stringAdded = true;
        break;

      //10110111 - P3 pin went low after pressing the button C
      case 119: // B10110111 -> D183
        Serial.print("C");
        pressedCharacter = "C";
        buttonPressed = true;
        stringAdded = true;
        break;
    }


    //========== Fourth row ============//
    Wire.beginTransmission(0x20);
    Wire.write(B01111111);
    //B[P7]01111111[P0] -> [P7]0111[P4] - activates second row, [P3]1111[P0] - Sets all pins high on the MUX
    Wire.endTransmission();

    Wire.requestFrom(0x20, 1);
    switch(Wire.read()) {
      //01111110 - P0 pin went low after pressing the button *
      case 126: // B01111110 -> D126
        Serial.print("*");
        pressedCharacter = "*";
        buttonPressed = true;
        stringAdded = true;
        break;

      //01111101 - P1 pin went low after pressing the button 0
      case 125: // B01111101 -> D125
        Serial.print("0");
        pressedCharacter = "0";
        buttonPressed = true;
        stringAdded = true;
        break;

      //01111011 - P2 pin went low after pressing the button #
      case 123: // B01111011 -> D123
        Serial.print("#");
        pressedCharacter = "#";
        buttonPressed = true;
        stringAdded = true;
        break;

      //01110111 - P3 pin went low after pressing the button D
      case 119: // B01110111 -> D119
        Serial.print("D");
        pressedCharacter = "D";
        buttonPressed = true;
        stringAdded = true;
        break;
    }
  }
}
**/