#include <Wire.h>

#define SDA_PIN 2      // your wiring
#define SCL_PIN 4      // your wiring

#define MCP23017_ADDR 0x20

// MCP23017 register addresses (BANK=0)
#define IODIRA   0x00
#define IODIRB   0x01
#define GPIOA    0x12
#define GPIOB    0x13
#define OLATA    0x14
#define OLATB    0x15

void mcpWriteRegister(uint8_t reg, uint8_t value) {
  Wire.beginTransmission(MCP23017_ADDR);
  Wire.write(reg);
  Wire.write(value);
  Wire.endTransmission();
}

uint8_t mcpReadRegister(uint8_t reg) {
  Wire.beginTransmission(MCP23017_ADDR);
  Wire.write(reg);
  Wire.endTransmission();

  Wire.requestFrom(MCP23017_ADDR, (uint8_t)1);
  if (Wire.available()) {
    return Wire.read();
  }
  return 0;
}

void mcpSetAllOutputs() {
  // 0 = output, 1 = input
  mcpWriteRegister(IODIRA, 0x00); // GPA0..7 outputs
  mcpWriteRegister(IODIRB, 0x00); // GPB0..7 outputs
}

void mcpSetAllLeds(bool on) {
  // For sinking config: LOW = LED on, HIGH = LED off
  uint8_t val = on ? 0x00 : 0xFF;

  mcpWriteRegister(OLATA, val);
  mcpWriteRegister(OLATB, val);
}

void mcpChasePattern(uint16_t delayMs) {
  // Run a single "dot" from GPA0..7 then GPB0..7
  for (int i = 0; i < 16; i++) {
    uint8_t valA = 0xFF; // all off (HIGH) in sinking config
    uint8_t valB = 0xFF;

    if (i < 8) {
      // Turn ON one LED on port A by pulling that bit LOW
      valA &= ~(1 << i);
    } else {
      // Turn ON one LED on port B
      int j = i - 8;
      valB &= ~(1 << j);
    }

    mcpWriteRegister(OLATA, valA);
    mcpWriteRegister(OLATB, valB);

    delay(delayMs);
  }
}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Serial.println("Starting MCP23017 test...");

  // Init I2C on your chosen pins
  Wire.begin(SDA_PIN, SCL_PIN);

  // Optional: slow down a bit for debugging, if needed
  // Wire.setClock(100000); // 100kHz

  // Set all pins as outputs
  mcpSetAllOutputs();

  // Turn all LEDs OFF first
  mcpSetAllLeds(false);
  delay(500);

  // Blink all LEDs a few times
  for (int i = 0; i < 3; i++) {
    Serial.println("Blink ON");
    mcpSetAllLeds(true);
    delay(500);

    Serial.println("Blink OFF");
    mcpSetAllLeds(false);
    delay(500);
  }

  Serial.println("Entering chase pattern...");
}

void loop() {
  // Chase the LEDs forever
  mcpChasePattern(150);
}