#include <Wire.h>

#define LCD_ADDR 0x3D      // 7-bit Adresse (SA0=VDD)
#define RESET_PIN 8

// Zeitvariablen
int sekunde = 0, minute = 0, stunde = 0;
int tag = 1, monat = 1, jahr = 2025;
unsigned long letzteAktualisierung = 0;

// Serielle Eingabe
String inputBuffer = "";

void lcdCommand(uint8_t cmd, bool cont = false) {
  Wire.write(cont ? 0x80 : 0x00); // Control Byte: Co=cont, RS=0
  Wire.write(cmd);
}

void lcdData(uint8_t data) {
  Wire.beginTransmission(LCD_ADDR);
  Wire.write(0x40); // Control Byte: Co=0, RS=1
  Wire.write(data);
  Wire.endTransmission();
}

void setContrast(uint8_t contrast) {
  // Contrast = 0–63 → C5/C4 (oberste 2 Bits), C3–C0 (unterste 4 Bits)
  uint8_t c5_c4 = (contrast >> 4) & 0x03;
  uint8_t c3_c0 = contrast & 0x0F;

  Wire.beginTransmission(LCD_ADDR);
  lcdCommand(0x39, true);                   // Function Set (RE=0, IS=1)
  lcdCommand(0x54 | c5_c4, true);           // Power Control (C5/C4)
  lcdCommand(0x70 | c3_c0, true);           // Contrast Set (C3–C0)
  lcdCommand(0x38, false);                  // Function Set (RE=0, IS=0)
  Wire.endTransmission();
}

void lcdInit() {
  digitalWrite(RESET_PIN, LOW); delay(5);
  digitalWrite(RESET_PIN, HIGH); delay(5);

  Wire.beginTransmission(LCD_ADDR);
  lcdCommand(0x3A, true); // Function Set: 8-bit, RE=1
  lcdCommand(0x09, true); // 4-line display
  lcdCommand(0x06, true); // Entry mode (bottom view)
  lcdCommand(0x1E, true); // Bias
  lcdCommand(0x39, true); // Function Set (RE=0, IS=1)
  lcdCommand(0x1B, true); // Internal OSC
  lcdCommand(0x6E, true); // Follower control
  lcdCommand(0x57, true); // Power control
  lcdCommand(0x72, true); // Contrast Set default
  lcdCommand(0x38, false);// Function Set (RE=0, IS=0)
  Wire.endTransmission();

  delay(10);
  lcdCommandSingle(0x01); // Clear Display
  delay(2);
  lcdCommandSingle(0x0C); // Display ON, Cursor OFF, Blink OFF
}

void lcdCommandSingle(uint8_t cmd) {
  Wire.beginTransmission(LCD_ADDR);
  lcdCommand(cmd, false);
  Wire.endTransmission();
}

void lcdSetCursor(uint8_t line, uint8_t pos) {
  uint8_t addr = 0x80;
  switch (line) {
    case 2: addr = 0xA0; break;
    case 3: addr = 0xC0; break;
    case 4: addr = 0xE0; break;
  }
  lcdCommandSingle(addr + pos);
}

void lcdPrint(const char* text) {
  while (*text) lcdData(*text++);
}

void updateClock() {
  unsigned long jetzt = millis();
  if (jetzt - letzteAktualisierung >= 1000) {
    letzteAktualisierung = jetzt;
    sekunde++;
    if (sekunde >= 60) {
      sekunde = 0; minute++;
      if (minute >= 60) {
        minute = 0; stunde++;
        if (stunde >= 24) {
          stunde = 0; tag++;
          int maxTage = 31;
          if (monat == 4 || monat == 6 || monat == 9 || monat == 11) maxTage = 30;
          else if (monat == 2) maxTage = 28;
          if (tag > maxTage) {
            tag = 1; monat++;
            if (monat > 12) {
              monat = 1; jahr++;
            }
          }
        }
      }
    }

    char datum[17];
    snprintf(datum, sizeof(datum), "%02d.%02d.%04d", tag, monat, jahr);
    lcdSetCursor(3, 0); lcdPrint("Datum:              ");
    lcdSetCursor(3, 7); lcdPrint(datum);

    char uhr[17];
    snprintf(uhr, sizeof(uhr), "%02d:%02d:%02d", stunde, minute, sekunde);
    lcdSetCursor(4, 0); lcdPrint("Uhrzeit:              ");
    lcdSetCursor(4, 5); lcdPrint(uhr);
  }
}

void parseSerialInput() {
  while (Serial.available()) {
    char c = Serial.read();
    if (c == '\n' || c == '\r') {
      if (inputBuffer.startsWith("SET ")) {
        int d, m, y, h, min, s;
        if (sscanf(inputBuffer.c_str(), "SET %d.%d.%d %d:%d:%d", &d, &m, &y, &h, &min, &s) == 6) {
          tag = constrain(d, 1, 31);
          monat = constrain(m, 1, 12);
          jahr = constrain(y, 2000, 2099);
          stunde = constrain(h, 0, 23);
          minute = constrain(min, 0, 59);
          sekunde = constrain(s, 0, 59);
          lcdSetCursor(1, 0); lcdPrint("Zeit gesetzt!   ");
        } else {
          lcdSetCursor(1, 0); lcdPrint("Fehler Eingabe! ");
        }
      }
      inputBuffer = "";
    } else {
      inputBuffer += c;
    }
  }
}

void setup() {
  pinMode(RESET_PIN, OUTPUT);
  Wire.begin();
  Serial.begin(9600);
  delay(100);

  lcdInit();
  setContrast(50); // Fester Kontrastwert

  lcdSetCursor(1, 0); lcdPrint("DOGM204 Zeit-Demo");
  lcdSetCursor(2, 0); lcdPrint("I2C-Display");
  Serial.println("Gib ein: SET TT.MM.JJJJ HH:MM:SS");
}

void loop() {
  updateClock();
  parseSerialInput();
}