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#include <Wire.h>
 
const int AT24CAddr = 0x50;
byte i = 1;
 
void AT24CWrite(int deviceaddress, unsigned int eeaddress, byte data) {
 
  int rdata = data;
 
  Wire.beginTransmission(deviceaddress);
  Wire.write(eeaddress >> 8); // MSB
  Wire.write(eeaddress & 0xFF); // LSB
  Wire.write(rdata);
  Wire.endTransmission();
  
}
 
int16_t AT24CRead(int deviceaddress, unsigned int eeaddress) {
    
  int16_t rdata = -1;
    
  Wire.beginTransmission(deviceaddress);
  Wire.write(eeaddress >> 8); // MSB
  Wire.write(eeaddress & 0xFF); // LSB
  Wire.endTransmission();
  Wire.requestFrom(deviceaddress,1);
  if (Wire.available()) rdata = Wire.read();
    
  return rdata;
  
}
 
void resetRec() {
  AT24CWrite(AT24CAddr, 0, 0);
  delay(10);  
}
 
void record() {
 
  uint32_t m = millis();
  byte t, state = HIGH;
 
  while (1) {
  
    // Wait for state change
    while (digitalRead(A0) == state) {
      if (millis() - m > 3000) {
        AT24CWrite(AT24CAddr, i, 0);
        return;
      }
    }
    // Record time
    t = (millis() - m) / 10;
    m = millis();
    AT24CWrite(AT24CAddr, i++, t);
    digitalWrite(13, state);
    delay(10);
    state = !state; 
 
  }  
    
}
 
void playback() {
 
  uint32_t m = millis();
  byte t, state = HIGH;
 
  while (t = AT24CRead(AT24CAddr, i++)) {
 
    delay((uint32_t)t * 10); 
    digitalWrite(13, state);
    state = !state;
    
  }
 
}
 
void setup() {
  
  pinMode(A0, INPUT_PULLUP);
  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);
 
  Wire.begin();
  
  // To reset the EEPROM data indicator:
  //resetRec();
  //return; 
 
  // Light goes off when ready to record/playback
  delay(1000);
  digitalWrite(13, LOW);
 
  Serial.println(AT24CRead(AT24CAddr, 0));
  if (AT24CRead(AT24CAddr, 0) != 123) {
    
    record();
    delay(10);
    if (i > 1) AT24CWrite(AT24CAddr, 0, 123); // Mark "recorded" 
    
  } else {
      playback(); 
      digitalWrite(13, LOW);
      while (1);
    }
  
}
 
void loop() {
 
  digitalWrite(13, !digitalRead(13));
  delay(50);  
 
}