#include <Adafruit_LiquidCrystal.h>

Adafruit_LiquidCrystal lcd(0);

int threshold[16] = {0, 72, 128, 174, 230, 259, 285, 306, 335, 351, 365, 377, 395, 404, 413, 422};
char keypad[16] = {'1', '2', '3', '+', '4', '5', '6', '-', '7', '8', '9', '*', '.', '0', '/', '='};

void setup() {
  lcd.begin(16, 2);
  lcd.print("Threshold Example");
  lcd.setBacklight(1);
}

void loop() {
  static String displayText = ""; // String to store the displayed text
  int sensorValue = analogRead(A0);
  char character = findCharacter(sensorValue);

  // Check if any button is pressed
  if (sensorValue < 610) {
    // Append the character to the displayed text
    displayText += character;

    // Update the LCD display
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print(displayText);
    lcd.setBacklight(1);

    // Delay to avoid multiple rapid button presses
    delay(100);
  }

  // Check if equals button is pressed
  if (character == '=') {
    // Parse and evaluate the expression
    float result = evaluateExpression(displayText);

    // Display the result on the LCD
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Result: ");
    lcd.setCursor(0, 1);
    lcd.print(result);
    lcd.setBacklight(1);

    // Clear the displayText for the next input
    displayText = "";

    // Delay to avoid multiple rapid button presses
    delay(100);
  }
}

char findCharacter(int value) {
  for (int i = 0; i < 16; i++) {
    if (value <= threshold[i]) {
      return keypad[i];
    }
  }
  // Handle the case where no button is pressed
  return ' ';  // Space character as an example
}

float evaluateExpression(String expression) {
  // Replace '*' with 'x' for easier parsing
  expression.replace("*", "x");

  // Evaluate the expression using the toFloat method
  return evaluate(expression);
}

float evaluate(String expression) {
  // Find the operator and split the expression
  int operatorIndex = findOperator(expression);
  if (operatorIndex != -1) {
    String left = expression.substring(0, operatorIndex);
    String right = expression.substring(operatorIndex + 1);

    float operand1 = left.toFloat();
    float operand2 = right.toFloat();

    // Perform the calculation based on the operator
    switch (expression[operatorIndex]) {
      case '+':
        return operand1 + operand2;
      case '-':
        return operand1 - operand2;
      case 'x':
        return operand1 * operand2;
      case '/':
        // Check for division by zero
        if (operand2 != 0) {
          return operand1 / operand2;
        } else {
          return 0; // Handle division by zero error
        }
      default:
        return 0; // Invalid operator
    }
  } else {
    // If no operator is found, parse the entire expression as a float
    return expression.toFloat();
  }
}

int findOperator(String expression) {
  // Find the index of the first operator ('+', '-', 'x', '/')
  for (int i = 0; i < expression.length(); i++) {
    if (expression[i] == '+' || expression[i] == '-' || expression[i] == 'x' || expression[i] == '/') {
      return i;
    }
  }
  return -1; // No operator found
}