#include <Arduino.h>
#include <CountUpDownTimer.h>

//Start button pins and state
const int BUTTON_START_PIN     = 2; //Digital pin 2 on the Uno
const int LED_START_BUTTON_PIN = 3; //Digital pin 3 on the Uno
int startButtonState           = 0; //0 = OFF, 1 = ON

//Stop button pins and state
const int BUTTON_STOP_PIN     = 4; //Digital pin 4 on the Uno
const int LED_STOP_BUTTON_PIN = 5; //Digital pin 5 on the Uno
int stopButtonState           = 0; //0 = OFF, 1 = ON

//Lamp pins
const int RELAY_LAMP_PIN      = 6; //Digital pin 6 on the Uno

//Shift register pins
const int SHIFT_DATA          = 11; //Digital pin 11 on Uno, pin 14 on 74HC595
const int SHIFT_CLK           = 12; //Digital pin 12 on Uno, pin 11 on 74HC595
const int SHIFT_LATCH         = 8;  //Digital pin 8 on Uno, pin 12 on 74HC595

//Byte array of digits from 0 to 9.
byte digits[10] = {       //    .GFEDCBA
                    0xC0, //0, b11000000
                    0xF9, //1, b11111001
                  	0xA4, //2, b10100100
                  	0xB0, //3, b10110000
                  	0x99, //4, b10011001
                  	0x92, //5, b10010010
                  	0x82, //6, b10000010
                  	0xF8, //7, b11111000
                  	0x80, //8, b10000000
                  	0x90  //9, b10010000
                  };

//State machine configuration
const int STATE_STANDBY   = 0; //State when awaiting for user input
const int STATE_COUNTDOWN = 1; //State when counting down to RUNNING
const int STATE_RUNNING   = 2; //State when the lamp is on
int state = STATE_STANDBY;     //Default to STANDBY

//Program cycle configuration
const int RUNTIME_COUNTDOWN = 8;  //8 seconds
const int RUNTIME_RUNNING   = 20; //20 seconds
CountUpDownTimer timer(DOWN);     //Countdown timer

void initButtons()
{
    //Set the buttons to INPUT
    pinMode(BUTTON_START_PIN, INPUT);
    pinMode(BUTTON_STOP_PIN, INPUT);

    //Set the button LEDs to OUTPUT
    pinMode(LED_START_BUTTON_PIN, OUTPUT);
    pinMode(LED_STOP_BUTTON_PIN, OUTPUT);

    //Set the button LEDs
    digitalWrite(LED_START_BUTTON_PIN, HIGH);
    digitalWrite(LED_STOP_BUTTON_PIN, LOW);
}

void initDisplay()
{
    //Set the shift register pin modes to OUTPUT
    pinMode(SHIFT_LATCH, OUTPUT);
    pinMode(SHIFT_CLK, OUTPUT);
    pinMode(SHIFT_DATA, OUTPUT);
}

void initRelays()
{
    //Set the lamp relay pin to OUTPUT and set it to LOW
    pinMode(RELAY_LAMP_PIN, OUTPUT);
    digitalWrite(RELAY_LAMP_PIN, LOW);
}

void updateDisplay(int value)
{
    /* Split the number into two integers. Add thirdDigit etc. when adding
     * more digits
     */
    int firstDigit = value / 10;
    int secondDigit = value % 10;

    //Set latch LOW so segments do not change while sending
    digitalWrite(SHIFT_LATCH, LOW);
    //Shift out the bits going in reverse, starting with the second
    shiftOut(SHIFT_DATA, SHIFT_CLK, MSBFIRST, digits[secondDigit]);
    shiftOut(SHIFT_DATA, SHIFT_CLK, MSBFIRST, digits[firstDigit]);
    //Set latch HIGH so the correct segments light up
    digitalWrite(SHIFT_LATCH, HIGH);
}

void setup()
{
    /* Setup the relays first to ensure they have the correct state before
    * starting.
    */
    initRelays();
    //Setup the buttons
    initButtons();
    //Setup the display
    initDisplay();
    //Set the display to 00
    updateDisplay(00);
}

void loop()
{
    //Process the timer before processing input
    bool timerTick = timer.Timer();
    //Only update the display when the time has changed
    if (timer.TimeHasChanged())
    {
        //Get the time value from the timer
        unsigned long timerValue = timer.ShowSeconds();
        updateDisplay(timerValue);
    }

    //Process the start button only when in STANDBY
    if (state == STATE_STANDBY)
    {
        //Read the start button's state
        startButtonState = digitalRead(BUTTON_START_PIN);
        //Check for the button press
        if (startButtonState == HIGH)
        {
            /* Debounce to prevent multi-fire before handling the button's
            *  state
            */
            delay(50);

            //Turn off the start button LED and turn on the stop button LED
            digitalWrite(LED_START_BUTTON_PIN, LOW);
            digitalWrite(LED_STOP_BUTTON_PIN, HIGH);

            //Change the state to COUNTDOWN
            state = STATE_COUNTDOWN;
            //Set the timer for 8 seconds and run it
            timer.SetTimer(0, 0, RUNTIME_COUNTDOWN);
            timer.StartTimer();
        }
    }

    //Process the stop button only when RUNNING or is in COUNTDOWN mode
    if ((state == STATE_COUNTDOWN ||
         state == STATE_RUNNING) && timerTick)
    {
        //Read the stop button's state
        stopButtonState = digitalRead(BUTTON_STOP_PIN);
        //Check for the button press
        if (stopButtonState == HIGH)
        {
            //Turn off the lamp
            digitalWrite(RELAY_LAMP_PIN, LOW);

            //Turn on the start button LED and turn off the stop button LED
            digitalWrite(LED_START_BUTTON_PIN, HIGH);
            digitalWrite(LED_STOP_BUTTON_PIN, LOW);

            //Change the state to STANDBY and stop the timer
            state = STATE_STANDBY;
            timer.StopTimer();
            //Set the display to 00
            updateDisplay(00);

            /* Debounce to prevent multi-fire before handling the button's
            *  state
            */
            delay(50); //debounce
        }
    }

    /* Check to see if the countdown has ended (when it is 00:00:00), and
     * update the state machine accordingly.
     */
    if (timer.ShowHours() == 0 && timer.ShowMinutes() == 0 &&
        timer.ShowSeconds() == 0)
    {
        //Change the state to RUNNING of we are in COUNTDOWN mode
        if (state == STATE_COUNTDOWN)
        {
            //Turn on the lamp
            digitalWrite(RELAY_LAMP_PIN, HIGH);
            //Change the state to RUNNING
            state = STATE_RUNNING;
            //Set the timer for 20 seconds and run it
            timer.SetTimer(0, 0, RUNTIME_RUNNING);
            timer.StartTimer();
        }
        //Change the state to STANDBY if we are RUNNING
        else if (state == STATE_RUNNING)
        {
            //Turn off the lamp
            digitalWrite(RELAY_LAMP_PIN, LOW);

            //Turn on the start button LED and turn off the stop button LED
            digitalWrite(LED_START_BUTTON_PIN, HIGH);
            digitalWrite(LED_STOP_BUTTON_PIN, LOW);

            //Set the state to STANDBY because the cycle has ended
            state = STATE_STANDBY;
        }
    }
}