#include <Keypad.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_ADDR 0x3C

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
byte rowPins[ROWS] = {10, 9, 8, 7}; // Connect to Arduino pins 9,8,7,6
byte colPins[COLS] = {6, 5, 4, 3}; // Connect to Arduino pins 5,4,3,2

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

bool astable = true;
String params[3] = {"", "", ""}; // 0: R1 (or R in mono), 1: R2 (astable only), 2: C
int units[3] = {1, 1, 0}; // R: 0=Ω,1=kΩ,2=MΩ; C: 0=pF,1=nF,2=µF,3=code
String r_unit_strs[3] = {" ", "k", "M"};
String c_unit_strs[4] = {"pF", "nF", "uF", "code"};
int current_param = 0;
bool show_results = false;
unsigned long blink_timer = 0;
bool show_arrow = true;

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR);
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.display();
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    handle_key(key);
  }

  if (!show_results && (millis() - blink_timer > 500)) {
    blink_timer = millis();
    show_arrow = !show_arrow;
  }

  display.clearDisplay();
  if (show_results) {
    draw_results();
  } else {
    draw_edit_screen();
  }
  display.display();
}

void handle_key(char key) {
  if (show_results) {
    if (key == 'A' || key == 'B') {
      show_results = false;
    }
    return;
  }

  // Edit screen handling
  int max_param = astable ? 2 : 1;
  if (key == 'A') { // Up
    if (current_param > 0) {
        current_param--;
    } else {
        current_param = max_param; // wrap around
    }
}else if (key == 'B') { // Down
    if (current_param < max_param) {
        current_param++;  // just move to next parameter
    } else {
        // Already at last field → show results
        show_results = true;
    }
} else if (key == 'C') { // Toggle units
    if (current_param == 2) { // C
      units[2] = (units[2] + 1) % 4;
    } else {
      units[current_param] = (units[current_param] + 1) % 3;
    }
  } else if (key == 'D') { // Toggle mode
    astable = !astable;
    current_param = 0; // Reset selection
  } else if (key >= '0' && key <= '9') {
    params[current_param] += key;
  } else if (key == '*') {
    if ((current_param != 2 || units[2] != 3) && params[current_param].indexOf('.') == -1) {
      params[current_param] += '.';
    }
  } else if (key == '#') {
    params[current_param] = "";
  }
}

void draw_edit_screen() {
  display.setCursor(0, 0);
  display.println("555 calculator");
  display.print(astable ? "Astable mode  " : "Monostable mode");
  display.println();

  int y = 16; // Approximate, assuming text size 1 (~8px per line, plus spacing)

  // R1 or R
  display.setCursor(0, y);
  display.print((current_param == 0 && show_arrow) ? ">" : " ");
  display.print(astable ? "R1: " : "R: ");
  display.print(params[0]);
  display.print(" ");
  display.println(r_unit_strs[units[0]]);
  y += 8;

  if (astable) {
    // R2
    display.setCursor(0, y);
    display.print((current_param == 1 && show_arrow) ? ">" : " ");
    display.print("R2: ");
    display.print(params[1]);
    display.print(" ");
    display.println(r_unit_strs[units[1]]);
    y += 8;
  }

  // C
  display.setCursor(0, y);
  display.print((current_param == (astable ? 2 : 1) && show_arrow) ? ">" : " ");
  display.print("C: ");
  display.print(params[2]);
  if (units[2] != 3) {
    display.print(" ");
    display.println(c_unit_strs[units[2]]);
  } else {
    display.println(); // No unit for code
  }
}

double parse_resistor(int idx) {
  if (params[idx].length() == 0) return 0.0;
  double val = atof(params[idx].c_str());
  double mult = (units[idx] == 0) ? 1.0 : (units[idx] == 1) ? 1000.0 : 1000000.0;
  return val * mult;
}

double parse_capacitor() {
  if (params[2].length() == 0) return 0.0;
  if (units[2] == 3) { // Code mode
    long num = atol(params[2].c_str());
    size_t digits = params[2].length();
    if (digits <= 2) {
      return num * 1e-12;
    } else {
      int exp = num % 10;
      long mant = num / 10;
      return mant * pow(10, exp) * 1e-12;
    }
  } else {
    double val = atof(params[2].c_str());
    double mult = (units[2] == 0) ? 1e-12 : (units[2] == 1) ? 1e-9 : 1e-6;
    return val * mult;
  }
}

void draw_results() {
  double r1 = parse_resistor(0);
  double r2 = astable ? parse_resistor(1) : 0.0;
  double c = parse_capacitor();

  if (c == 0.0 || (astable && (r1 + r2 == 0.0)) || (!astable && r1 == 0.0)) {
    display.setCursor(0, 0);
    display.println("Invalid values");
    return;
  }

  display.setCursor(0, 0);
  display.println("Results:");

  if (astable) {
    double freq = 1.44 / ((r1 + 2 * r2) * c);
    double duty = (r1 + r2) / (r1 + 2 * r2) * 100.0;
    double period = 1.0 / freq;
    double t_high = 0.693 * (r1 + r2) * c;
    double t_low = 0.693 * r2 * c;

    display.print("Freq: ");
    display.print(freq, 2);
    display.println(" Hz");

    display.print("Duty: ");
    display.print(duty, 2);
    display.println(" %");

    display.print("Period: ");
    display.print(period, 6);
    display.println(" s");

    display.print("T High: ");
    display.print(t_high, 6);
    display.println(" s");

    display.print("T Low: ");
    display.print(t_low, 6);
    display.println(" s");
  } else {
    double pulse = 1.1 * r1 * c;

    display.print("Pulse: ");
    display.print(pulse, 6);
    display.println(" s");
  }
}