#include <Wire.h>

// Pin definitions
#define ENCODER_CLK 2
#define ENCODER_DT 3
#define OLED_WIDTH 128
#define OLED_HEIGHT 64

// State variables
int lastStateCLK;
int rotationAngle = 0;

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

      // Initialize I2C communication for OLED
        Wire.begin();

          // Set up the pins for the rotary encoder
            pinMode(ENCODER_CLK, INPUT);
              pinMode(ENCODER_DT, INPUT);

                // Read the initial state of the encoder
                  lastStateCLK = digitalRead(ENCODER_CLK);

                    // Initialize OLED
                      initializeOLED();
                      }

                      void loop() {
                        // Read the current state of the rotary encoder
                          int currentStateCLK = digitalRead(ENCODER_CLK);

                            // If the state has changed, determine rotation direction
                              if (currentStateCLK != lastStateCLK) {
                                  if (digitalRead(ENCODER_DT) != currentStateCLK) {
                                        rotationAngle += 10; // Rotate clockwise
                                            } else {
                                                  rotationAngle -= 10; // Rotate counterclockwise
                                                      }

                                                          // Constrain the rotation angle to 0-359 degrees
                                                              if (rotationAngle >= 360) rotationAngle -= 360;
                                                                  if (rotationAngle < 0) rotationAngle += 360;

                                                                      // Display the arrow on the OLED
                                                                          drawArrow(rotationAngle);
                                                                            }

                                                                              // Save the last state of the CLK pin
                                                                                lastStateCLK = currentStateCLK;
                                                                                }

                                                                                // Function to initialize the OLED display
                                                                                void initializeOLED() {
                                                                                  Wire.beginTransmission(0x3C); // The I2C address of the SSD1306
                                                                                    Wire.write(0x00); // Command mode
                                                                                      Wire.write(0xAE); // Display OFF
                                                                                        Wire.write(0x20); // Set memory addressing mode
                                                                                          Wire.write(0x00); // Horizontal addressing mode
                                                                                            Wire.write(0xB0); // Set page start address for page addressing mode
                                                                                              Wire.write(0xC8); // COM scan direction
                                                                                                Wire.write(0x00); // Set lower column address
                                                                                                  Wire.write(0x10); // Set higher column address
                                                                                                    Wire.write(0x40); // Set display start line
                                                                                                      Wire.write(0x81); // Set contrast control
                                                                                                        Wire.write(0x7F);
                                                                                                          Wire.write(0xA1); // Segment remap
                                                                                                            Wire.write(0xA6); // Normal display
                                                                                                              Wire.write(0xA8); // Set multiplex ratio
                                                                                                                Wire.write(0x3F); // 1/64 duty
                                                                                                                  Wire.write(0xA4); // Display follow RAM
                                                                                                                    Wire.write(0xD3); // Set display offset
                                                                                                                      Wire.write(0x00); // No offset
                                                                                                                        Wire.write(0xD5); // Set display clock divide ratio
                                                                                                                          Wire.write(0xF0); // Highest frequency
                                                                                                                            Wire.write(0xD9); // Set pre-charge period
                                                                                                                              Wire.write(0x22); 
                                                                                                                                Wire.write(0xDA); // Set com pins hardware configuration
                                                                                                                                  Wire.write(0x12);
                                                                                                                                    Wire.write(0xDB); // Set vcomh
                                                                                                                                      Wire.write(0x20); // 0.77x Vcc
                                                                                                                                        Wire.write(0x8D); // Charge pump
                                                                                                                                          Wire.write(0x14);
                                                                                                                                            Wire.write(0xAF); // Display ON
                                                                                                                                              Wire.endTransmission();
                                                                                                                                              }

                                                                                                                                              // Function to draw the arrow based on the angle
                                                                                                                                              void drawArrow(int angle) {
                                                                                                                                                clearDisplay();

                                                                                                                                                  // Calculate the end point of the arrow based on the angle
                                                                                                                                                    int x0 = OLED_WIDTH / 2;
                                                                                                                                                      int y0 = OLED_HEIGHT / 2;
                                                                                                                                                        int arrowLength = 20;

                                                                                                                                                          float radians = angle * 3.14159 / 180.0;
                                                                                                                                                            int x1 = x0 + arrowLength * cos(radians);
                                                                                                                                                              int y1 = y0 + arrowLength * sin(radians);

                                                                                                                                                                drawLine(x0, y0, x1, y1);

                                                                                                                                                                  updateDisplay();
                                                                                                                                                                  }

                                                                                                                                                                  // Function to clear the OLED display
                                                                                                                                                                  void clearDisplay() {
                                                                                                                                                                    Wire.beginTransmission(0x3C);
                                                                                                                                                                      Wire.write(0x00); // Command mode
                                                                                                                                                                        for (int i = 0; i < 1024; i++) {
                                                                                                                                                                            Wire.write(0x00);
                                                                                                                                                                              }
                                                                                                                                                                                Wire.endTransmission();
                                                                                                                                                                                }

                                                                                                                                                                                // Function to draw a line on the OLED display (Bresenham's algorithm)
                                                                                                                                                                                void drawLine(int x0, int y0, int x1, int y1) {
                                                                                                                                                                                  int dx = abs(x1 - x0);
                                                                                                                                                                                    int dy = abs(y1 - y0);
                                                                                                                                                                                      int sx = x0 < x1 ? 1 : -1;
                                                                                                                                                                                        int sy = y0 < y1 ? 1 : -1;
                                                                                                                                                                                          int err = dx - dy;

                                                                                                                                                                                            while (true) {
                                                                                                                                                                                                setPixel(x0, y0);
                                                                                                                                                                                                    if (x0 == x1 && y0 == y1) break;
                                                                                                                                                                                                        int e2 = err * 2;
                                                                                                                                                                                                            if (e2 > -dy) {
                                                                                                                                                                                                                  err -= dy;
                                                                                                                                                                                                                        x0 += sx;
                                                                                                                                                                                                                            }
                                                                                                                                                                                                                                if (e2 < dx) {
                                                                                                                                                                                                                                      err += dx;
                                                                                                                                                                                                                                            y0 += sy;
                                                                                                                                                                                                                                                }
                                                                                                                                                                                                                                                  }
                                                                                                                                                                                                                                                  }

                                                                                                                                                                                                                                                  // Function to set a pixel on the OLED display
                                                                                                                                                                                                                                                  void setPixel(int x, int y) {
                                                                                                                                                                                                                                                    if (x < 0 || x >= OLED_WIDTH || y < 0 || y >= OLED_HEIGHT) return;

                                                                                                                                                                                                                                                      Wire.beginTransmission(0x3C);
                                                                                                                                                                                                                                                        Wire.write(0x40); // Data mode
                                                                                                                                                                                                                                                          Wire.write(0xFF); // Pixel on
                                                                                                                                                                                                                                                            Wire.endTransmission();
                                                                                                                                                                                                                                                            }

                                                                                                                                                                                                                                                            // Function to update the OLED display
                                                                                                                                                                                                                                                            void updateDisplay() {
                                                                                                                                                                                                                                                              Wire.beginTransmission(0x3C);
                                                                                                                                                                                                                                                                Wire.write(0x00); // Command mode
                                                                                                                                                                                                                                                                  Wire.write(0x21); // Set column address
                                                                                                                                                                                                                                                                    Wire.write(0x00);
                                                                                                                                                                                                                                                                      Wire.write(OLED_WIDTH - 1);
                                                                                                                                                                                                                                                                        Wire.write(0x22); // Set page address
                                                                                                                                                                                                                                                                          Wire.write(0x00);
                                                                                                                                                                                                                                                                            Wire.write((OLED_HEIGHT / 8) - 1);
                                                                                                                                                                                                                                                                              Wire.endTransmission();
                                                                                                                                                                                                                                                                              }