#include <Wire.h>
#include "RTClib.h"

//Real time clock
RTC_DS1307 rtc;

// Digit segments labels:
//
//     a 
//    ---
// f |   | b
//    --- g
// e |   | c
//    ---
//     d
//

// mapping between segments and registry for digits managed by MCP23017 port expander
                   // a   b   c   d   e   f   g
int segmentsA[7] = { 16, 64,  8,  2,  1, 32,  4};
int segmentsB[7] = {  1,  4, 16, 32, 64,  2,  8};

// mapping between arduino ports and segments for digits managed directly by Arduino
                   // a   b   c   d   e   f   g
int segmentsC[7] = {  2,  0, 10, 13,  9,  4,  8};
int segmentsD[7] = {  5,  7,  6, 12, 11,  1,  3};

// mapping between digits and segments bits configuration
byte digits[10] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};

void setup() {

  //i2c setup
  Wire.begin();
  
  //setup MCP23017 registries
  Wire.beginTransmission(0x20);
  Wire.write(0x00); // IODIRA register
  Wire.write(0x00); // set all of port A to outputs
  Wire.endTransmission();
  Wire.beginTransmission(0x20);
  Wire.write(0x01); // IODIRB register
  Wire.write(0x00); // set all of port B to outputs
  Wire.endTransmission();

  //setup arduino ports
  for (int i = 0; i< 14; i++) pinMode(i, OUTPUT);
  
  //RTC setup
  rtc.begin();
  
  if (! rtc.isrunning()) {
    // following line sets the RTC to the date & time this sketch was compiled
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  }
  
  //clear clock digits
  clearClock();
}

void loop() {
  
  //get time from RTC
  DateTime now = rtc.now();

  //prints hour and minutes
  print(now.hour(), now.minute());
  
  delay(500);
}

//prints hour and minute
void print(int hour, int min) {
  printHour(hour);
  printMinute(min);
}

//prints hour digits
void printHour(int hour) {
  
  //extract the two digits from the hour value
  int h = hour%100;
  int hd1 = h%10;
  int hd2 = (h/10)%10;
  
  int d1 = mapSegments(segmentsA, hd1);
  int d2 = mapSegments(segmentsB, hd2);
  
  writeARegistry(d1);
  writeBRegistry(d2);
}

//prints the minute digits
void printMinute(int min) {
  
  //extract the two digits from the minute value
  int m = min%100;
  int d1 = m%10;
  int d2 = (m/10)%10;
  
  printDigit(segmentsC, d2);
  printDigit(segmentsD, d1);
}

//clear the clock digits
void clearClock() {
  
  writeARegistry(0);
  writeBRegistry(0);
  
  clearDigit(segmentsC);
  clearDigit(segmentsD);
}


/** HELPERS **/

//writes into the A registry of MCP23017
void writeARegistry(int value) {
  Wire.beginTransmission(0x20);
  Wire.write(0x12); // GPIOA
  Wire.write(value); // port A
  Wire.endTransmission();
}

//writes into the B registry of MCP23017
void writeBRegistry(int value) {
  Wire.beginTransmission(0x20);
  Wire.write(0x13); // GPIOB
  Wire.write(value); // port B
  Wire.endTransmission();
}

//translate the digit into a registry bits configuration
byte mapSegments(int segments[], int digit) {
  
  //the segments configuration
  byte bits = digits[digit];
  int pow = 1;
  
  //registry configuration
  int registryBits = 0;
  for (int i = 0; i< 7; i++) {
    registryBits += (pow & bits)?segments[i]:0;
    pow = pow*2;
  }
  return registryBits;
}

//turn on the segments for the specified digit
void printDigit(int segments[], int digit) {
  
  //segments configuration
  byte bits = digits[digit];
  
  int pow = 1;
  for (int i = 0; i< 7; i++) {
    //turns on the segment based on digit configuration
    digitalWrite(segments[i], pow & bits?HIGH:LOW);
    pow = pow*2;
  }
}

//turn off all the specified segments
void clearDigit(int segments[]) {
  for (int i = 0; i< 7; i++) digitalWrite(segments[i], LOW);
}

//turn on all the specified segments
void all(int segments[]) {
  for (int i = 0; i< 7; i++) digitalWrite(segments[i], HIGH);
}