// Clock example using a seven segment display & GPS for time.
//
// Must have the Adafruit GPS library installed too!  See:
//   https://github.com/adafruit/Adafruit-GPS-Library
//
// Designed specifically to work with the Adafruit LED 7-Segment backpacks
// and ultimate GPS breakout/shield:
// ----> http://www.adafruit.com/products/881
// ----> http://www.adafruit.com/products/880
// ----> http://www.adafruit.com/products/879
// ----> http://www.adafruit.com/products/878
// ----> http://www.adafruit.com/products/746
//
// Adafruit invests time and resources providing this open source code, 
// please support Adafruit and open-source hardware by purchasing 
// products from Adafruit!
//
// Written by Tony DiCola for Adafruit Industries.
// Released under a MIT license: https://opensource.org/licenses/MIT
#include <SoftwareSerial.h>
#include <Wire.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"
#include "Adafruit_GPS.h"


// Set to false to display time in 12 hour format, or true to use 24 hour:
#define TIME_24_HOUR      false

// Offset the hours from UTC (universal time) to your local time by changing
// this value.  The GPS time will be in UTC so lookup the offset for your
// local time from a site like:
//   https://en.wikipedia.org/wiki/List_of_UTC_time_offsets
// This value, -7, will set the time to UTC-7 or Pacific Standard Time during
// daylight savings time.
#define HOUR_OFFSET       -7

// I2C address of the display.  Stick with the default address of 0x70
// unless you've changed the address jumpers on the back of the display.
#define DISPLAY_ADDRESS   0x70


// Create display and GPS objects.  These are global variables that
// can be accessed from both the setup and loop function below.
Adafruit_7segment clockDisplay = Adafruit_7segment();
SoftwareSerial gpsSerial(8, 7);  // GPS breakout/shield will use a 
                                 // software serial connection with 
                                 // TX = pin 8 and RX = pin 7.
Adafruit_GPS gps(&gpsSerial);


void setup() {
  // Setup function runs once at startup to initialize the display and GPS.

  // Setup Serial port to print debug output.
  Serial.begin(115200);
  Serial.println("Clock starting!");

  // Setup the display.
  clockDisplay.begin(DISPLAY_ADDRESS);

  // Setup the GPS using a 9600 baud connection (the default for most
  // GPS modules).
  gps.begin(9600);

  // Configure GPS to onlu output minimum data (location, time, fix).
  gps.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCONLY);

  // Use a 1 hz, once a second, update rate.
  gps.sendCommand(PMTK_SET_NMEA_UPDATE_1HZ);
  
  // Enable the interrupt to parse GPS data.
  enableGPSInterrupt();
}

void loop() {
  // Loop function runs over and over again to implement the clock logic.

  // Check if GPS has new data and parse it.
  if (gps.newNMEAreceived()) {
    gps.parse(gps.lastNMEA());
  }
  
  // Grab the current hours, minutes, seconds from the GPS.
  // This will only be set once the GPS has a fix!  Make sure to add
  // a coin cell battery so the GPS will save the time between power-up/down.
  int hours = gps.hour + HOUR_OFFSET;  // Add hour offset to convert from UTC
                                       // to local time.
  // Handle when UTC + offset wraps around to a negative or > 23 value.
  if (hours < 0) {
    hours = 24+hours;
  }
  if (hours > 23) {
    hours = 24-hours;
  }
  int minutes = gps.minute;
  int seconds = gps.seconds;
  
  // Show the time on the display by turning it into a numeric
  // value, like 3:30 turns into 330, by multiplying the hour by
  // 100 and then adding the minutes.
  int displayValue = hours*100 + minutes;

  // Do 24 hour to 12 hour format conversion when required.
  if (!TIME_24_HOUR) {
    // Handle when hours are past 12 by subtracting 12 hours (1200 value).
    if (hours > 12) {
      displayValue -= 1200;
    }
    // Handle hour 0 (midnight) being shown as 12.
    else if (hours == 0) {
      displayValue += 1200;
    }
  }

  // Now print the time value to the display.
  clockDisplay.print(displayValue, DEC);

  // Add zero padding when in 24 hour mode and it's midnight.
  // In this case the print function above won't have leading 0's
  // which can look confusing.  Go in and explicitly add these zeros.
  if (TIME_24_HOUR && hours == 0) {
    // Pad hour 0.
    clockDisplay.writeDigitNum(1, 0);
    // Also pad when the 10's minute is 0 and should be padded.
    if (minutes < 10) {
      clockDisplay.writeDigitNum(2, 0);
    }
  }

  // Blink the colon by turning it on every even second and off
  // every odd second.  The modulus operator is very handy here to
  // check if a value is even (modulus 2 equals 0) or odd (modulus 2
  // equals 1).
  clockDisplay.drawColon(seconds % 2 == 0);

  // Now push out to the display the new values that were set above.
  clockDisplay.writeDisplay();

  // Loop code is finished, it will jump back to the start of the loop
  // function again! Don't add any delays because the parsing needs to 
  // happen all the time!
}

SIGNAL(TIMER0_COMPA_vect) {
  // Use a timer interrupt once a millisecond to check for new GPS data.
  // This piggybacks on Arduino's internal clock timer for the millis()
  // function.
  gps.read();
}

void enableGPSInterrupt() {
  // Function to enable the timer interrupt that will parse GPS data.
  // Timer0 is already used for millis() - we'll just interrupt somewhere
  // in the middle and call the "Compare A" function above
  OCR0A = 0xAF;
  TIMSK0 |= _BV(OCIE0A);
}
