#include <WiFi.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <time.h>

// ==========================
// OLED display settings
// ==========================
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ==========================
// WiFi credentials
// ==========================
const char *ssid = "Wokwi-GUEST";
const char *password = "";

// ==========================
// Switch settings (4-bit binary)
// ==========================
#define SW0 2   // LSB
#define SW1 3
#define SW2 4
#define SW3 5   // MSB

int lastTZ = -1;  // store previous value to detect changes

// ==========================
// Timezone definitions (16 total)
// ==========================
struct Timezone {
  const char* tz;   // TZ database string
  const char* name; // Display name
};

Timezone timezones[] = {
  { "GMT0",                         "GMT/UTC" },
  { "IST-2IDT,M3.4.4/26,M10.5.0",   "Israel" },
  { "EST5EDT,M3.2.0,M11.1.0",       "US Eastern" },
  { "CST6CDT,M3.2.0,M11.1.0",       "US Central" },
  { "MST7MDT,M3.2.0,M11.1.0",       "US Mountain" },
  { "PST8PDT,M3.2.0,M11.1.0",       "US Pacific" },
  { "GMT0BST,M3.5.0/1,M10.5.0",     "London" },
  { "CET-1CEST,M3.5.0,M10.5.0/3",   "Central Europe" },
  { "EET-2EEST,M3.5.0/3,M10.5.0/4", "Eastern Europe" },
  { "MSK-3",                        "Moscow" },
  { "JST-9",                        "Tokyo" },
  { "KST-9",                        "Seoul" },
  { "IST-5:30",                     "Delhi" },
  { "HKT-8",                        "Hong Kong" },
  { "AEST-10AEDT,M10.1.0,M4.1.0/3", "Sydney" },
  { "NZST-12NZDT,M9.5.0,M4.1.0/3",  "New Zealand" }
};

const int timezoneCount = sizeof(timezones) / sizeof(timezones[0]);
int currentTZ = 0;

// ==========================
// Display refresh
// ==========================
unsigned long lastUpdate = 0;
const long updateInterval = 1000;

void setup() {
  Serial.begin(115200);
  Wire.begin(8, 9);

  // Setup switches
  pinMode(SW0, INPUT_PULLUP);
  pinMode(SW1, INPUT_PULLUP);
  pinMode(SW2, INPUT_PULLUP);
  pinMode(SW3, INPUT_PULLUP);

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;);
  }

  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.display();

  // Connect WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  // Configure NTP
  configTime(0, 0, "pool.ntp.org", "time.nist.gov");
  applyTimezone();
}

void applyTimezone() {
  setenv("TZ", timezones[currentTZ].tz, 1);
  tzset();
  Serial.print("Switched timezone to: ");
  Serial.println(timezones[currentTZ].name);
}

// Read switches as binary number
int readSwitches() {
  int val = (digitalRead(SW0) == LOW ? 1 : 0)
          | (digitalRead(SW1) == LOW ? 2 : 0)
          | (digitalRead(SW2) == LOW ? 4 : 0)
          | (digitalRead(SW3) == LOW ? 8 : 0);
  return val;
}

String formatTwoDigits(int number) {
  return number < 10 ? "0" + String(number) : String(number);
}

String getFormattedDate(struct tm *timeinfo) {
  String day = formatTwoDigits(timeinfo->tm_mday);
  String month = formatTwoDigits(timeinfo->tm_mon + 1);
  String year = String(timeinfo->tm_year + 1900);
  return day + "/" + month + "/" + year;
}

String get12HourTime(struct tm *timeinfo) {
  int hour = timeinfo->tm_hour;
  String period = hour < 12 ? " AM" : " PM";
  if (hour == 0) hour = 12;
  else if (hour > 12) hour -= 12;
  return formatTwoDigits(hour) + ":" + formatTwoDigits(timeinfo->tm_min) + " " + period;
}

void drawCenteredText(String text, int y, int textSize) {
  display.setTextSize(textSize);
  int16_t x1, y1;
  uint16_t w, h;
  display.getTextBounds(text, 0, 0, &x1, &y1, &w, &h);
  display.setCursor((SCREEN_WIDTH - w) / 2, y);
  display.print(text);
}

void loop() {
  // ==========================
  // Handle switch input
  // ==========================
  int newTZ = readSwitches();
  if (newTZ != lastTZ && newTZ < timezoneCount) {
    currentTZ = newTZ;
    applyTimezone();
    lastTZ = newTZ;
  }

  // ==========================
  // Update display
  // ==========================
  if (millis() - lastUpdate >= updateInterval) {
    lastUpdate = millis();

    struct tm timeinfo;
    if (!getLocalTime(&timeinfo)) {
      Serial.println("Failed to get time");
      return;
    }

    display.clearDisplay();

    // DATE
    display.fillRect(0, 0, SCREEN_WIDTH, 20, SSD1306_WHITE);
    display.setTextColor(SSD1306_BLACK);
    drawCenteredText(getFormattedDate(&timeinfo), 5, 2);

    // TIME
    display.setTextColor(SSD1306_WHITE);
    String timeStr = get12HourTime(&timeinfo);
    drawCenteredText(timeStr.substring(0, 6), 28, 3);

    // AM/PM
    display.setTextSize(2);
    display.setCursor((SCREEN_WIDTH / 2) + 40, 32);
    display.print(timeStr.substring(7));

    // TZ name
    display.setTextSize(1);
    drawCenteredText(String("Zone: ") + timezones[currentTZ].name, 56, 1);

    display.display();
  }

  // WiFi reconnect
  if (millis() % 10000 == 0 && WiFi.status() != WL_CONNECTED) {
    WiFi.reconnect();
  }
}