// https://forum.arduino.cc/t/calipers-angle-measurement/1393255/4

#include <TinyDebug.h> // for serial monitor output
// tdPrintln("Not using SRAM"); // example Serial.println();

// #include <avr/pgmspace.h> // for memory

#include "SSD1306_minimal.h"
SSD1306_Mini oled; // 0.42" display 72x40

byte buttonpin = PB3, potpin = A2;
int potval, potvalold, minval, maxval;
char vals[6];

#define CHARWIDTH 6 // pixel width of a character and kern

void setup() {
  oled.init(0x3C); // Initialize display with address
  oled.clear(); // Clears the display
  pinMode(buttonpin, INPUT_PULLUP);
  pinMode(potpin, OUTPUT);

  calibrate_pot();
  show_min_max();
}

void loop() {
  read_pot();
}

int read_pot() {
  potval = analogRead(potpin);
  if (potval != potvalold) {
    oled.cursorTo(1, 1);
    oled.printString("          "); // clear display

    if (potval < minval) {
      oled.cursorTo(1, 1);
      oled.printString(" < MINVAL ");
    }
    if (potval > maxval) {
      oled.cursorTo(1, 1);
      oled.printString(" > MAXVAL ");
    }
    if ((potval >= minval) && (potval <= maxval)) {
      int_to_char_array(potval, 1);
    }
  }
  potvalold = potval;
}

void calibrate_pot() {
  for (byte i = 0; i < 2; i++) {
    oled.cursorTo(0, 0); // col 0 to 7, row 0 to 3

    if (i == 0) {
      oled.printString("SET MIN.");
      tdPrintln("Move pot to set min. Then press button.");
    }  else {
      oled.printString("SET MAX.");
      tdPrintln("Move pot to set max. Then press button.");
    }
    press_to_continue();

    if (i == 0)
      // minval = read_pot();
      minval = analogRead(potpin);
    else
      // maxval = read_pot();
      maxval = analogRead(potpin);

    oled.cursorTo(0, 1);
    if (i == 0)
      oled.printString("min set.");
    else
      oled.printString("max set.");
    press_to_continue();

    oled.clear();
  }
}

void show_min_max() {
  oled.cursorTo(2, 0);
  oled.printString("MIN");
  int_to_char_array(minval, 0);

  oled.cursorTo(2, 1);
  oled.printString("MAX");
  int_to_char_array(maxval, 1);

  press_to_continue();
  oled.clear();
}

void int_to_char_array(int val, int row) {
  int tens = val / 1000;
  int ones = (val - (tens * 1000)) / 100;
  int tnts = (val - (tens * 1000) - (ones * 100)) / 10;
  int hnds = (val - (tens * 1000) - (ones * 100) - (tnts * 10)) / 1;

  vals[0] = tens + '0';
  vals[1] = ones + '0';
  vals[2] = '.';
  vals[3] = tnts + '0';
  vals[4] = hnds + '0';

  for (byte i = 0; i < 5; i++) {
    oled.cursorTo((5 * CHARWIDTH) + (i * CHARWIDTH), row);
    oled.printChar(vals[i]);
  }
}

void press_to_continue() {
  oled.cursorTo(0, 3);
  oled.printString(">button<");
  while (digitalRead(buttonpin) == HIGH);
  delay(250); // fast readings need delay
}