/*
 * I2C Communication Demo - ESP32 + SSD1306 OLED
 * ================================================
 * Demonstrates I2C protocol by communicating with an SSD1306 OLED display.
 * 
 * What students will see:
 *   - ESP32 (Master) sends commands/data to OLED (Slave) over I2C
 *   - OLED displays text, proving I2C communication works
 *   - Serial Monitor shows I2C bus scanning and protocol details
 *   - Logic Analyzer can capture SDA/SCL waveforms
 * 
 * Wiring:
 *   ESP32 GPIO21 (SDA) <--> OLED SDA  [Data line - bidirectional]
 *   ESP32 GPIO22 (SCL) <--> OLED SCL  [Clock line - Master controlled]
 *   ESP32 3V3          <--> OLED VCC
 *   ESP32 GND          <--> OLED GND
 * 
 * Protocol: I2C (Inter-Integrated Circuit)
 *   - Synchronous: Master generates clock on SCL
 *   - Half-duplex: Data on SDA, one direction at a time
 *   - Addressed: Each slave has a 7-bit address (OLED = 0x3C)
 *   - ACK/NACK: Slave acknowledges each byte received
 *   - Multi-slave: Multiple devices can share same SDA/SCL bus
 * 
 * Libraries needed (add to libraries.txt):
 *   Wire (built-in)
 *   Adafruit GFX Library
 *   Adafruit SSD1306
 */

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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_ADDR_1 0x3C   // 7-bit I2C address of SSD1306
#define OLED_ADDR_2 0x3D

// Create display object connected to I2C (Wire)
Adafruit_SSD1306 display1(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
Adafruit_SSD1306 display2(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

int counter = 0;

// Scan the I2C bus and report all devices found
void scanI2CBus() {
  Serial.println("[I2C SCAN] Scanning bus for devices...");
  Serial.println("  Address range: 0x01 to 0x7F (7-bit)");
  Serial.println();

  int devicesFound = 0;
  for (byte addr = 1; addr < 127; addr++) {
    Wire.beginTransmission(addr);       // START + address + Write bit
    byte error = Wire.endTransmission(); // Check for ACK

    if (error == 0) {
      Serial.print("  [FOUND] Device at address: 0x");
      if (addr < 16) Serial.print("0");
      Serial.print(addr, HEX);

      // Identify known devices
      if (addr == 0x3C || addr == 0x3D) {
        Serial.print("  --> SSD1306 OLED Display");
      }
      Serial.println();
      devicesFound++;
    }
  }

  Serial.print("  Total devices found: ");
  Serial.println(devicesFound);
  Serial.println();
}

void setup() {
  Serial.begin(115200);
  Serial.println("==========================================");
  Serial.println("  I2C Communication Demo (ESP32 + OLED)");
  Serial.println("==========================================");
  Serial.println();
  Serial.println("I2C Bus Configuration:");
  Serial.println("  SDA: GPIO21 (data line)");
  Serial.println("  SCL: GPIO22 (clock line)");
  Serial.println("  Mode: Standard (100 kHz)");
  Serial.println("  Role: ESP32 = Master, OLED = Slave");
  Serial.println("----------------------------------------");

  // Initialize I2C bus
  Wire.begin(21, 22);

  // Step 1: Scan for I2C devices
  scanI2CBus();

  // Step 2: Initialize the OLED display
  Serial.println("[INIT] Starting SSD1306 at address 0x3C...");
  if (!display1.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR_1)) {
    Serial.println("[ERROR] SSD1306 not found! Check wiring.");
    while (1);
  }
  if (!display2.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR_2)) {
    Serial.println("[ERROR] SSD1306 not found! Check wiring.");
    while (1);
  }
  Serial.println("[INIT] OLED initialized successfully!");
  Serial.println();

  // Step 3: Show welcome message on OLED
  display1.clearDisplay();
  display1.setTextSize(2);
  display1.setTextColor(SSD1306_WHITE);
  display1.setCursor(10, 5);
  display1.println("I2C Demo");
  display1.setTextSize(1);
  display1.setCursor(10, 30);
  display1.println("ESP32 -> SSD1306_1");
  display1.setCursor(10, 45);
  display1.println("Addr: 0x3C");
  display1.display();  // This sends the buffer over I2C!

  display2.clearDisplay();
  display2.setTextSize(2);
  display2.setTextColor(SSD1306_WHITE);
  display2.setCursor(10, 5);
  display2.println("I2C Demo");
  display2.setTextSize(1);
  display2.setCursor(10, 30);
  display2.println("ESP32 -> SSD1306_2");
  display2.setCursor(10, 45);
  display2.println("Addr: 0x3D");
  display2.display();  // This sends the buffer over I2C!

  Serial.println("[I2C TX] Sent display buffer to OLED");
  Serial.println("  Transaction breakdown:");
  Serial.println("  1. START condition (SDA goes LOW while SCL HIGH)");
  Serial.println("  2. Address byte: 0x3C + Write bit = 0x78");
  Serial.println("  3. Slave sends ACK");
  Serial.println("  4. Data bytes (display buffer: 1024 bytes)");
  Serial.println("  5. STOP condition");
  Serial.println("----------------------------------------");

  delay(3000);
}

void loop() {
  counter++;

  // Update the OLED display with new data
  display1.clearDisplay();
  display1.setTextSize(2);
  display1.setTextColor(SSD1306_WHITE);
  display1.setCursor(10, 5);
  display1.println("Counter:");
  display1.setTextSize(3);
  display1.setCursor(30, 30);
  display1.println(counter);
  display1.display();  // Send updated buffer via I2C

  display2.clearDisplay();
  display2.setTextSize(2);
  display2.setTextColor(SSD1306_WHITE);
  display2.setCursor(10, 5);
  display2.println("Counter:");
  display2.setTextSize(3);
  display2.setCursor(30, 30);
  display2.println(counter);
  display2.display();  // Send updated buffer via I2C

  Serial.print("[I2C TX] Updated display, counter = ");
  Serial.println(counter);

  delay(10);
}