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

// Define OLED display size
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

// Define I2C address
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Analog pin for battery voltage
#define BATTERY_PIN A0

// Voltage divider resistors (if used)
#define R1 10000 // 10k ohm
#define R2 10000 // 10k ohm

// Maximum and minimum battery voltages
#define MAX_BATTERY_VOLTAGE 4.2
#define MIN_BATTERY_VOLTAGE 3.0

void setup() {
  // Initialize serial communication
  Serial.begin(9600);

  // Initialize OLED display
  if (!display.begin(  SSD1306_PAGEADDR, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;);
  }
  display.clearDisplay();
  display.display();

  // Display welcome message
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.println(F("Battery Monitor"));
  display.display();
  delay(2000);
}

void loop() {
  // Read analog value
  int analogValue = analogRead(BATTERY_PIN);

  // Convert to voltage (Assuming a 5V reference and 10-bit ADC)
  float voltage = analogValue * (5.0 / 1023.0);

  // If using a voltage divider, adjust for the divider ratio
  voltage = voltage * ((R1 + R2) / R2);

  // Calculate battery capacity percentage
  float capacity = map(voltage * 100, MIN_BATTERY_VOLTAGE * 100, MAX_BATTERY_VOLTAGE * 100, 0, 100);
  capacity = constrain(capacity, 0, 100);

  // Print values to the serial monitor
  Serial.print("Voltage: ");
  Serial.print(voltage);
  Serial.print(" V, Capacity: ");
  Serial.print(capacity);
  Serial.println(" %");

  // Display values on OLED
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);

  // Voltage
  display.setCursor(0, 0);
  display.print(F("Voltage: "));
  display.print(voltage, 2);
  display.println(F(" V"));

  // Capacity
  display.setCursor(0, 20);
  display.print(F("Capacity: "));
  display.print(capacity, 0);
  display.println(F(" %"));

  // Battery bar
  display.drawRect(0, 40, 100, 10, SSD1306_WHITE); // Outer rectangle
  display.fillRect(1, 41, capacity, 8, SSD1306_WHITE); // Fill based on capacity

  display.display();
  delay(1000); // Update every second
}