unsigned int time = 0; // profile seconds
unsigned int temperatur = 25; // actual oven temp
unsigned int last_temperatur = 25;

unsigned int Ts_max = 200; // °C
unsigned int Ts_min = 150; // °C
unsigned int Tp = 260; // 245-260°C
unsigned int rampup_rate = 3; // 3°C/s
unsigned int preheat_duration = 100; // 60-180s
unsigned int tal = 217; // 217°C
unsigned int tal_duration = 100; // 60-150s
unsigned int peak_duration = 30; // 20-40s
unsigned int rampdown_max = 6; // 6°C/s max
unsigned int time_max = 480; // 8*60s max

#define START_STATE 0
#define PREHEAT_STATE 1
#define TAL_STATE 2
#define MAX_STATE 3
#define RAMPDOWN_STATE 4
#define END_STATE 5
#define ERROR_STATE 6

byte state = START_STATE;

unsigned int Ts_min_time = 0;
unsigned int Ts_max_time = 0;
unsigned int Tl_time = 0;
unsigned int Tp_time = 0;
unsigned int Tl_end_time = 0;

#define RAMPUP_TOO_FAST 1
#define RAMPDOWN_TOO_FAST 2
unsigned int error_condition = 0;


void setup() {
  pinMode(13, OUTPUT);
  Serial.begin(9600);
}

void get_temp() {
  // simulating an +1K/s rampup oven
  last_temperatur = temperatur++;
}

boolean check_rampup_rate() {
  if (temperatur - last_temperatur > rampup_rate) {
    error_condition = RAMPUP_TOO_FAST;
    return false;
  }
  return true;
}

void loop() {
  time = millis() / 1000;
  get_temp();
  Serial.print(time);
  Serial.print(" ");
  Serial.print(temperatur);
  Serial.print(" ");
  Serial.println(last_temperatur);

  delay(1000);

  switch (state) {
      case START_STATE:
          // going from room temp to preheat, nothing to check here
          if (!check_rampup_rate())
              goto error;
          if (temperatur > Ts_min) {
              state++;
          }
      case PREHEAT_STATE:
          if (temperatur > Ts_max) {
            Serial.println("Changed state to PREHEAT_STATE");
            state++;
          }
          break;
      case TAL_STATE:
        break;
      case MAX_STATE:
        break;
      case RAMPDOWN_STATE:
        break;
      default:
        break;
  }

  return;

error:
  state = END_STATE;
  Serial.println(error_condition);
}