import time
from machine import I2C, Pin

class SHTC3:
    """Utility class for Sensirion SHTC3 Temperature and Humidity Sensor."""
    ADDR = 0x70
    
    # Commands
    WAKE = b'\x35\x17'
    SLEEP = b'\xB0\x98'
    MEASURE = b'\x78\x66' # High precision, T first, clock stretching disabled

    def __init__(self, i2c=None):
        if i2c is None:
            # Default to ESP32-S3-RLCD-4.2 onboard I2C pins
            self.i2c = I2C(0, sda=Pin(13), scl=Pin(14))
        else:
            self.i2c = i2c

    def _crc8(self, data):
        """Sensirion CRC-8 checksum calculation (polynom 0x31, init 0xFF)."""
        crc = 0xFF
        for byte in data:
            crc ^= byte
            for _ in range(8):
                if crc & 0x80:
                    crc = (crc << 1) ^ 0x31
                else:
                    crc <<= 1
                crc &= 0xFF
        return crc

    def read_sensor(self):
        """Wakes up the sensor, reads temp and humidity, validates CRC, and sleeps.
        
        Returns:
            tuple: (temperature_c, relative_humidity_pct) or (None, None) on error.
        """
        try:
            # 1. Wakeup
            self.i2c.writeto(self.ADDR, self.WAKE)
            time.sleep_ms(1)
            
            # 2. Trigger Measurement
            self.i2c.writeto(self.ADDR, self.MEASURE)
            time.sleep_ms(15) # High precision measurement takes up to 12.1ms
            
            # 3. Read 6 bytes of data
            # bytes 0, 1: Temp, byte 2: Temp CRC
            # bytes 3, 4: Hum,  byte 5: Hum CRC
            data = self.i2c.readfrom(self.ADDR, 6)
            
            # 4. Enter low-power sleep mode
            self.i2c.writeto(self.ADDR, self.SLEEP)
            
            # Verify CRC
            t_data = data[0:2]
            t_crc = data[2]
            h_data = data[3:5]
            h_crc = data[5]
            
            if self._crc8(t_data) != t_crc:
                print("SHTC3 Temp CRC error")
                return None, None
            if self._crc8(h_data) != h_crc:
                print("SHTC3 Hum CRC error")
                return None, None
                
            raw_t = (data[0] << 8) | data[1]
            raw_h = (data[3] << 8) | data[4]
            
            # Formula from datasheet
            temp = -45.0 + 175.0 * (raw_t / 65536.0)
            hum = 100.0 * (raw_h / 65536.0)
            
            return round(temp, 2), round(hum, 2)
            
        except Exception as e:
            print(f"Error reading SHTC3 sensor: {e}")
            # Try to send sleep command anyway to save power
            try:
                self.i2c.writeto(self.ADDR, self.SLEEP)
            except:
                pass
            return None, None