/* This is the sketch that is uploaded on the Xiao RP2040.
 * The Xiao acts as a master device on the I2C bus to send and
 * receive message from the slave at address 8.
 */

#include <Wire.h>

String input = "";  // stores the input message for echoing on the serial monitor

void setup() {
  Wire.begin();        // join I2C bus (address optional for master)
  Serial.begin(9600);  // start serial for output
}

void loop() {
  Wire.beginTransmission(8);      // Sends a '0' to indicate that we are listening
  Wire.write(0);
  Wire.endTransmission();
  int l = Wire.requestFrom(8, 1); // Read from peer
  if (l == 1) {                   // A '1' means the peer is sending
    char n = Wire.read();         // First read the length of the message
    if (n > 0) {                  // If we have any data
      Wire.beginTransmission(8);  // Send '1' means we are requesting the data
      Wire.write(1);
      Wire.endTransmission();
      Wire.requestFrom(8, n);     // request n bytes from slave device #8
      while (Wire.available()) {  // slave may send less than requested
        char c = Wire.read();     // receive a byte as character
        Serial.print(c);          // print the character
      }
    }
  }

  // Take input from the computer
  if (Serial.available() > 0) {
    Wire.beginTransmission(8);    // Starts sending message to peer
    Wire.write(2);                // A '2' indicates the master is sending
    while (Serial.available() > 0) {
      char c = Serial.read();
      Wire.write(c);              // Send the message to peer

      input += c;                 // Collects the input message
      if (c == '\n') {            // Print the message that we sent and reset the buffer
        Serial.print("me: ");
        Serial.print(input);
        input = "";
      }
    }
    Wire.endTransmission();
  }
}