#include <Wire.h>
#include <stdlib.h>

#define SLAVE_ADDRESS 0x16

const int xpin = A0;                  // x-axis of the accelerometer
const int ypin = A1;                  // y-axis
const int zpin = A2;                  // z-axis (only on 3-axis models)
int index = 0;
char data[40];

void setup() {
  //Serial.begin(9600);
  pinMode(xpin, INPUT);
  pinMode(ypin, INPUT);
  pinMode(zpin, INPUT);
  // initialize i2c as slave
  Wire.begin(SLAVE_ADDRESS);
  Wire.onRequest(sendData);
}

void loop() {
  // Nothing to do at last !!!!
}

void sendData() {
  read_lilypad();
  Wire.write(data[index]); 
  index++;
  if (index >= 40) {
    index = 0;
  }
}

//Function that reads the data from the Lilypad sensor
void read_lilypad () {
  int x_input = analogRead(xpin);
  int y_input = analogRead(ypin);
  int z_input = analogRead(zpin);

  //zero_G is the reading we expect from the sensor when it detects
  //no acceleration.  Subtract this value from the sensor reading to
  //get a shifted sensor reading.
  //float x_zero_G = 515.39;
  //float y_zero_G = 508.57;
  //float z_zero_G = 513.19;
  
  float x_zero_G = 401.01;
  float y_zero_G = 407.15;
  float z_zero_G = 474.69;

  //scale is the number of units we expect the sensor reading to
  //change when the acceleration along an axis changes by 1G.
  //Divide the shifted sensor reading by scale to get acceleration in Gs.
  float scale = 102.3;

  //Calculate values and convert them to string

  String x_value = String(((float)x_input - x_zero_G) / scale);
  String y_value = String(((float)y_input - y_zero_G) / scale);
  String z_value = String(((float)z_input - z_zero_G) / scale);
  
  //Putting all values to one string
  String lilypad = "Lilypad x: " + x_value + " y: " + y_value + " z: " + z_value;
  
/*  Saving The string to an array to be send to master */
  lilypad.toCharArray(data, 40);

}