// global
  // libs
    #include <Wire.h>
    #include <Adafruit_GFX.h>
    #include <Adafruit_SSD1306.h>
  // pins
    uint8_t pi_textSize = A15;
    uint8_t pp_down = 23, pp_up = 53;
  // defs
    const uint32_t c_bttn_debounce_time = 80;
    const uint8_t c_text_rows[8] = { 8, 8, 4, 2, 2, 1, 1, 1 };
    const uint8_t c_text_cols[8] = { 21, 21, 10, 7, 5, 4, 3, 3 };
  // vars
    uint8_t text_size_last = 10;
      uint8_t text_rowsMax = 0;
      uint8_t text_colsMax = 0;
    uint8_t cursor[2] = { 0, 0 };
    uint32_t fn_root = 0;

    bool up_state = 0, down_state = 0;
    uint32_t bttn_debounce_timer = 0;
  // init
    Adafruit_SSD1306 display(128, 64, &Wire, -1); // decl SSD1306 SDI, I2C pins
  // macros
    // set display
      #define updCursor() (display.setCursor(cursor[0], cursor[1]))
      #define space() (display.print(F(" ")))
    // get vals
      #define maxRows() (c_text_rows[text_size_last])
      #define maxCols() (c_text_cols[text_size_last])
    // inputs
      #define readSize() (analogRead(pi_textSize)>>8)
      //#define readTextSize() (analogRead(pi_textSize)>>7)
      #define readUp() (!digitalRead(pp_up))
      #define readDown() (!digitalRead(pp_down))
      #define isDebounced() ((c_bttn_debounce_time+bttn_debounce_timer)<millis())

void setup() {
  // pins
    pinMode(pi_textSize, INPUT);
    pinMode(pp_up, INPUT_PULLUP);
      pinMode(pp_down, INPUT_PULLUP);
  // screen
    bool displayLaunched = display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // Address 0x3D for 128x64
    display.clearDisplay();
    display.setTextColor(WHITE);
    updCursor();
}

// notes
  // text sizing
    // size 0/1 - 21 col, 8 row
    // size   2 - 10 col, 4 row
    // size   3 - 7  col, 2 row
    // size   4 - 5  col, 2 row
    // size   5 - 4  col, 1 row
    // size   6 - 3  col, 1 row
    // size   7 - 3  col, 1 row


void loop() { 
  // handle inputs
    bool disp_update = false;
    if (isDebounced()) {
      if (readUp() ^ up_state) {
        up_state^=1;
        fn_root+=(bool)up_state;
        disp_update|=up_state;
        bttn_debounce_timer = millis();
      }
      if (readDown() ^ down_state) {
        down_state^=1;
        fn_root-=(bool)down_state;
        disp_update|=down_state;
        bttn_debounce_timer = millis();
      }
    }
    disp_update |= updateTextSize();

  // update display (if needed)
    if (disp_update) dispChars(fn_root);

}

void dispChars(uint32_t minChar) {
  display.clearDisplay();
  setCursor();
  uint32_t maxChar = minChar+text_rowsMax;
  for (uint32_t i=minChar; i<maxChar; i++) {
    while (i == '\n') {
      i++;
      maxChar++;
    }
    display.print(i, DEC);
    display.print(F(" - "));
    display.write(i);
    
    if (text_size_last<3) {
      //display.print(F("  "));
      space();
      for (uint8_t j=0; j<2; j++) display.write(i);
    }
    display.println();
  }
  display.display();
}

bool updateTextSize() {
  uint8_t text_size_new = readSize();
  bool textSize_changed_flag = (text_size_new!=text_size_last);
  text_size_last = text_size_new;
  if (textSize_changed_flag) {
    updCursor();
    display.setTextSize(text_size_last);
  }
  text_rowsMax = maxRows();
  text_colsMax = maxCols();
  return textSize_changed_flag;
}

void setCursor() {
  setCursor(0, 0);
}
void setCursor(uint8_t y, uint8_t x) {
  cursor[0] = y;
  cursor[1] = x;
  updCursor();
}

void spaceOut(uint32_t num) {
  if (num<10) space();
  if (num<100) space();
  if (num<1000) display.print(F("-"));
}