// tool libraries
#include <U8g2lib.h>

#define OLED_CENTER_X 64
#define OLED_CENTER_Y 64
#define OLED_MAX_X 128
#define OLED_MAX_Y 128

#define BOX_WIDTH 30
#define BOX_HEIGHT 10
#define BOX_MAX_X (OLED_MAX_X - BOX_WIDTH)
// How much the box moves per tick
#define BOX_VELOCITY 5

// Instantiate graphics library object
U8G2_SH1107_128X128_1_HW_I2C u8g2(U8G2_R0);

// buttons
#define LEFT_BUTTON_INPUT_PIN 8
#define LEFT_BUTTON_STATE_PIN 9
#define RIGHT_BUTTON_INPUT_PIN 7
#define RIGHT_BUTTON_STATE_PIN 6
#define DEBOUNCE_DELAY_MS 10

typedef struct button {
  int buttonRawInputPin;
  int buttonStateOutputPin;
  int steadyButtonState;
  int rawButtonState;
  unsigned long lastTransTimeMs;
} button;

// Button pins - used to initialize and THEN used to keep button state;
button *left = malloc(sizeof(button));
button *right = malloc(sizeof(button));

// box variables
int boxX = 0;
// Setup at bottom of screen
int boxY = OLED_MAX_Y - BOX_HEIGHT;

void configButtonPin(int pin, int direction, button *btn) {
  if (direction == INPUT) {
    (*btn).buttonRawInputPin = pin;
    pinMode((*btn).buttonRawInputPin, INPUT);
  }
  else if (direction == OUTPUT) {
    (*btn).buttonStateOutputPin = pin;
    pinMode((*btn).buttonStateOutputPin, OUTPUT);
  }
}

void buttonUpdate(button *btn) {
  int reading = digitalRead((*btn).buttonRawInputPin);

  // reset debounce timer on transition
  if (reading != (*btn).rawButtonState) {
    (*btn).lastTransTimeMs = millis();
    (*btn).rawButtonState = reading;
  }

  // Otherwise check for timer elapsing, button state can update
  else if ((millis() - (*btn).lastTransTimeMs) > DEBOUNCE_DELAY_MS) {
    (*btn).steadyButtonState = (*btn).rawButtonState;
  }

  // write output status pin
  digitalWrite((*btn).buttonStateOutputPin, (*btn).steadyButtonState);
}

void setup() {
  // Serial output baud config
  Serial.begin(115200);

  // button setup
  configButtonPin(LEFT_BUTTON_INPUT_PIN, INPUT, left);
  configButtonPin(LEFT_BUTTON_STATE_PIN, OUTPUT, left);
  configButtonPin(RIGHT_BUTTON_INPUT_PIN, INPUT, right);
  configButtonPin(RIGHT_BUTTON_STATE_PIN, OUTPUT, right);

  u8g2.begin();  // begin the u8g2 library
  u8g2.setContrast(255);
  u8g2.setFont(u8g2_font_8x13B_mr);
  u8g2.setDrawColor(1); // set the drawing color to white 
}

void loop() {
  // update button via debouncing utility
  buttonUpdate(left);
  buttonUpdate(right);

  if ((*left).steadyButtonState == HIGH) {
    if (boxX >= BOX_VELOCITY) {
      boxX -= BOX_VELOCITY;
    }
    else {
      boxX -= boxX;
    }
    Serial.print("New x-coor = ");
    Serial.println(boxX);
  }
  if ((*right).steadyButtonState == HIGH) {
    if ((BOX_MAX_X - boxX) >= BOX_VELOCITY) {
      boxX += BOX_VELOCITY;
    }
    else {
      boxX += (BOX_MAX_X - boxX);
    }
    Serial.print("New x-coor = ");
    Serial.println(boxX);
  }

  u8g2.firstPage(); // select the first page of the display (page is 128x8px), since we are using the page drawing method of the u8g2 library
  do { // draw
    u8g2.drawBox(boxX, boxY, BOX_WIDTH, BOX_HEIGHT);
  } while ( u8g2.nextPage() ); // go over all the pages until the whole display is updated
}