#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);  

}