/*
 * ATtiny85 Raspberry Pi Power Controller
 *
 * Arduino pin 0 / PB0 = PSU enable
 * Arduino pin 1 / PB1 = Status LED
 * Arduino pin 2 / PB2 = Power button to GND
 * Arduino pin 3 / PB3 = Shutdown request to Pi GPIO16
 * Arduino pin 4 / PB4 = Pi alive input from Pi GPIO26
 *
 * ATtiny runs at 5 V.
 * PB3 is open-drain style:
 *   idle = INPUT / Hi-Z
 *   shutdown request = OUTPUT LOW
 */



#define PSU_ENABLE_PIN     0
#define LED_PIN            1
#define BUTTON_PIN         2
#define SHUTDOWN_PIN       3
#define PI_ALIVE_PIN       4

#define BOOT_GRACE_MS      60000UL
#define SHUTDOWN_HOLD_MS   1000UL
#define POWEROFF_DELAY_MS  70000UL // 10000UL is enough for normal shutdowns, 70000UL accomadate pi restarts
#define DEBOUNCE_MS        50UL

bool systemOn = false;
bool shutdownRequested = false;
bool buttonLast = HIGH;

unsigned long powerOnTime = 0;

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);

  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);

  pinMode(PSU_ENABLE_PIN, OUTPUT);
  digitalWrite(PSU_ENABLE_PIN, LOW);

  pinMode(SHUTDOWN_PIN, OUTPUT);
  digitalWrite(SHUTDOWN_PIN, LOW);


  pinMode(PI_ALIVE_PIN, INPUT);


  
}

void loop() {
  updateLed();
  handleButton();
  monitorPiAliveOrTimeout();

  delay(20);
}

void updateLed() {
  if (systemOn) {
    digitalWrite(LED_PIN, HIGH);   // solid ON when Pi power is on
    return;
  }

  // Slow heartbeat when PSU is off:
  // ON 80 ms, OFF 120 ms, ON 80 ms, OFF 720 ms
  unsigned long t = millis() % 1000UL;

  if ((t < 80UL) || (t >= 200UL && t < 280UL)) {
    digitalWrite(LED_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
  }
}

void handleButton() {
  bool button = digitalRead(BUTTON_PIN);

  if (button == LOW && buttonLast == HIGH) {
    delay(DEBOUNCE_MS);

    if (digitalRead(BUTTON_PIN) == LOW) {
      if (!systemOn) {
        turnSystemOn();
      } else if (!shutdownRequested) {
        requestPiShutdown();
      }
    }
  }

  buttonLast = button;
}

void turnSystemOn() {
  digitalWrite(PSU_ENABLE_PIN, HIGH);
  systemOn = true;
  shutdownRequested = false;
  powerOnTime = millis();
}

void requestPiShutdown() {
  // Pull Pi GPIO16 LOW.
  // Turn on the SS8050 transistor
  
  digitalWrite(SHUTDOWN_PIN, HIGH);

  delay(SHUTDOWN_HOLD_MS);

  digitalWrite(SHUTDOWN_PIN, LOW);

  shutdownRequested = true;
}

void monitorPiAliveOrTimeout() {
  if (!systemOn) return;

  // Ignore alive pin while Pi is booting
  if (millis() - powerOnTime < BOOT_GRACE_MS) return;

  // Pi GPIO26 via gpio-poweroff:
  // HIGH = Pi running
  // LOW  = Pi halted / safe to power off
  if (digitalRead(PI_ALIVE_PIN) == LOW) {
    delay(POWEROFF_DELAY_MS);

    if (digitalRead(PI_ALIVE_PIN) == LOW) {
      turnSystemOff();
      return;
    }
  }

}

void turnSystemOff() {
  digitalWrite(PSU_ENABLE_PIN, LOW);
  systemOn = false;
  shutdownRequested = false;
  digitalWrite(LED_PIN, LOW);
}