#include <M5Stack.h>

#define KEYBOARD_I2C_ADDR 0X08
#define KEYBOARD_INT      5

float Num1 = 0;
float Num2 = 0;
float Num3 = 0;
float Num4 = 0;
char Fun;
char Fun2;
char Fun3;
int CalNum  = 0;
int SumFlag = 0;
float Sum;
String Datain;
uint8_t key_val;

void setup() {
    M5.begin();
    Wire.begin();
    M5.Lcd.setTextFont(4);
    pinMode(KEYBOARD_INT, INPUT_PULLUP);
    CalNum = 1;
    Draw_Screen();
}

void loop() {
    if (digitalRead(KEYBOARD_INT) == LOW) {
        Wire.requestFrom(KEYBOARD_I2C_ADDR, 1);  // request 1 byte from keyboard

        while (Wire.available()) {
            uint8_t key_val = Wire.read();  // receive a byte as character
            if (key_val != 0) {
                if (isDigit(key_val) || key_val == '.') {
                    if (SumFlag == 1) {
                        StoreData();
                    }
                    Datain += (char)key_val;
                    IsNumber();
                }

                if (key_val == 'A' || key_val == '+' || key_val == '-' ||
                    key_val == '*' || key_val == '/' || key_val == '=') {
                    FunKey(key_val);
                }
            }
        }
    }
}

void FunKey(uint8_t key_in) {
    switch (key_in) {
        case 'A':
            M5.Lcd.clear();
            Draw_Screen();
            Num1   = 0;
            Num2   = 0;
            Sum    = 0;
            Datain = "                     ";
            CalNum = 1;
            break;

        case '=':
            if (Fun == '+') {
                Sum = Num1 + Num2;
            }

            if (Fun == '-') {
                Sum = Num1 - Num2;
            }

            if (Fun == '*') {
                Sum = Num1 * Num2;
            }

            if (Fun == '/') {
                Sum = Num1 / Num2;
            }

            M5.Lcd.setCursor(105, 190);
            M5.Lcd.print(Sum);
            SumFlag = 1;
            break;

        case '+':
            Fun = '+';
            CalNum += 1;
            Datain = "                 ";
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print("   ");
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print(Fun);
            break;

        case '-':
            Fun = '-';
            CalNum += 1;
            Datain = "                 ";
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print("   ");
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print(Fun);
            break;

        case '*':
            Fun = '*';
            CalNum += 1;
            Datain = "                 ";
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print("   ");
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print(Fun);
            break;

        case '/':
            Fun = '/';
            CalNum += 1;
            Datain = "                 ";
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print("   ");
            M5.Lcd.setCursor(20, 140);
            M5.Lcd.print(Fun);
            break;

        default:
            break;
    }
}

void StoreData(void) {
    Num1    = Sum;
    Num2    = 0;
    SumFlag = 0;
    Datain  = "                     ";
    M5.Lcd.setCursor(20, 140);
    M5.Lcd.print(Fun);
    M5.Lcd.setCursor(70, 100);
    M5.Lcd.print("                  ");
    M5.Lcd.setCursor(70, 140);
    M5.Lcd.print("                  ");
    M5.Lcd.setCursor(70, 100);
    M5.Lcd.print(Num1);
    M5.Lcd.setCursor(105, 190);
    M5.Lcd.print("                 ");
}

void IsNumber(void) {
    if (CalNum == 1) {
        Num1 = Datain.toFloat();
        M5.Lcd.setCursor(70, 100);
        M5.Lcd.print(Num1);
    }

    if (CalNum >= 2) {
        Num2 = Datain.toFloat();
        M5.Lcd.setCursor(70, 140);
        M5.Lcd.print(Num2);
    }
}

void DrawBox(int LocX, int LocY, int W, int H) {
    M5.Lcd.drawLine(LocX, LocY, LocX + W, LocY, TFT_WHITE);
    M5.Lcd.drawLine(LocX, LocY + H, LocX + W, LocY + H, TFT_WHITE);
    M5.Lcd.drawLine(LocX, LocY, LocX, LocY + H, TFT_WHITE);
    M5.Lcd.drawLine(LocX + W, LocY, LocX + W, LocY + H, TFT_WHITE);
}

void Draw_Screen(void) {
    M5.Lcd.clear();
    M5.Lcd.drawLine(1, 180, 320, 180, TFT_WHITE);
    M5.Lcd.setCursor(15, 20);
    M5.Lcd.print("FRACTION CALCULATOR");
    DrawBox(50, 95, 250, 32);
    DrawBox(10, 135, 30, 32);
    DrawBox(50, 135, 250, 32);
    M5.Lcd.setCursor(10, 190);
    M5.Lcd.print("SUM  =");
}