/**
 * Program: Temperature, Pressure and Altitude Monitoring with BMP280
 * 
 * This program uses a BMP280 sensor to measure temperature, pressure and altitude,
 * displaying the values on an SSD1306 OLED display.
 * 
 * Connections:
 * - BMP280 connected via SPI:
 *   - SCK: pin 13
 *   - MISO: pin 12
 *   - MOSI: pin 11
 *   - CS: pin 10
 * - OLED connected via I2C (SDA, SCL)
 */

#include <Wire.h>
#include <U8glib.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BMP280.h>
#include <SPI.h>

// Constants
#define SEA_LEVEL_PRESSURE 1013.25  // Sea level pressure in hPa (standard)
#define UPDATE_DELAY 1000           // Time between updates (1 seconds)

// Define SPI pins for BMP280
#define BMP_SCK  13  // SPI Clock
#define BMP_MISO 12  // SPI MISO
#define BMP_MOSI 11  // SPI MOSI
#define BMP_CS   10  // Chip Select

// BMP280 sensor instance using SPI
Adafruit_BMP280 bmp_sensor(BMP_CS, BMP_MOSI, BMP_MISO, BMP_SCK);

// OLED display instance
U8GLIB_SSD1306_128X64 u8g(U8G_I2C_OPT_FAST);

/**
 * Initialize the BMP280 sensor via SPI
 * Returns true if the sensor was successfully initialized
 */
bool initBMP280() {
  if (!bmp_sensor.begin()) {
    Serial.println("BMP280 sensor not found. Check SPI connections!");
    return false;
  }
  
  // Optional sensor configurations
  bmp_sensor.setSampling(Adafruit_BMP280::MODE_NORMAL,     /* Operation mode */
                         Adafruit_BMP280::SAMPLING_X2,     /* Temperature oversampling */
                         Adafruit_BMP280::SAMPLING_X16,    /* Pressure oversampling */
                         Adafruit_BMP280::FILTER_X16,      /* Filtering */
                         Adafruit_BMP280::STANDBY_MS_500); /* Standby time */
                         
  return true;
}

/**
 * Initialize the OLED display
 */
void initDisplay() {
  // Display color settings
  if (u8g.getMode() == U8G_MODE_R3G3B2) {
    u8g.setColorIndex(255);  // white
  } 
  else if (u8g.getMode() == U8G_MODE_GRAY2BIT) {
    u8g.setColorIndex(3);    // maximum intensity
  } 
  else if (u8g.getMode() == U8G_MODE_BW) {
    u8g.setColorIndex(1);    // pixel on
  } 
  else if (u8g.getMode() == U8G_MODE_HICOLOR) {
    u8g.setHiColorByRGB(255, 255, 255);
  }
}

/**
 * Draw the interface on the OLED display with sensor data
 */
void drawInterface() {
  // Font settings
  u8g.setFont(u8g_font_8x13B);
  
  // Draw frames
  u8g.drawRFrame(0, 16, 128, 48, 4);  // Main frame
  u8g.drawRFrame(0, 0, 128, 16, 4);   // Title frame
  
  // Title
  u8g.drawStr(25, 13, "BMP280 SPI");
  
  // Temperature
  float temperature = bmp_sensor.readTemperature();
  u8g.drawStr(10, 31, "Temp:      C");
  u8g.drawCircle(93, 22, 2);  // Degree symbol
  u8g.setPrintPos(55, 31);
  u8g.print(temperature, 1);  // 1 decimal place
  
  // Pressure (in hPa)
  float pressure = bmp_sensor.readPressure() / 100.0F; // Convert to hPa
  u8g.drawStr(10, 45, "Pres:      hPa");
  u8g.setPrintPos(55, 45);
  u8g.print(pressure, 1);  // 1 decimal place
  
  // Altitude
  float altitude = bmp_sensor.readAltitude(SEA_LEVEL_PRESSURE);
  u8g.drawStr(10, 59, "Alt:       m");
  u8g.setPrintPos(55, 59);
  u8g.print(altitude, 1);  // 1 decimal place
}

/**
 * Update the display with current sensor information
 */
void updateDisplay() {
  u8g.firstPage();
  do {
    drawInterface();
  } while (u8g.nextPage());
}

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  Serial.println("Starting BMP280 monitoring system via SPI");
  
  // Initialize SPI communication
  SPI.begin();
  
  // Initialize the BMP280 sensor
  if (!initBMP280()) {
    Serial.println("Sensor initialization failed. Check connections!");
    while (1); // Halt execution if the sensor is not found
  }
  
  // Initialize the OLED display
  initDisplay();
  
  Serial.println("System successfully initialized");
}

void loop() {
  // Update the display with current data
  updateDisplay();
  
  // Print data to serial monitor
  float temperature = bmp_sensor.readTemperature();
  float pressure = bmp_sensor.readPressure() / 100.0F; // Convert to hPa
  float altitude = bmp_sensor.readAltitude(SEA_LEVEL_PRESSURE);
  
  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" °C");
  
  Serial.print("Pressure: ");
  Serial.print(pressure);
  Serial.println(" hPa");
  
  Serial.print("Approx. altitude: ");
  Serial.print(altitude);
  Serial.println(" m");
  Serial.println("-------------------");
  
  // Wait before the next update
  delay(UPDATE_DELAY);
}