"""CircuitPython SHTC3 temperature and humidity sensor driver.

Uses standard I2C transactions with bus locking.
"""

import time

class SHTC3:
    ADDR = 0x70

    WAKE = b'\x35\x17'
    SLEEP = b'\xB0\x98'
    MEASURE = b'\x78\x66' # High precision, T first, clock stretching disabled

    def __init__(self, i2c):
        self.i2c = i2c

    def _crc8(self, data):
        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):
        try:
            # 1. Wakeup
            while not self.i2c.try_lock():
                pass
            try:
                self.i2c.writeto(self.ADDR, self.WAKE)
            finally:
                self.i2c.unlock()
            time.sleep(0.001)

            # 2. Trigger Measurement
            while not self.i2c.try_lock():
                pass
            try:
                self.i2c.writeto(self.ADDR, self.MEASURE)
            finally:
                self.i2c.unlock()
            time.sleep(0.015)

            # 3. Read 6 bytes of data
            # bytes 0, 1: Temp, byte 2: Temp CRC
            # bytes 3, 4: Hum,  byte 5: Hum CRC
            buf = bytearray(6)
            while not self.i2c.try_lock():
                pass
            try:
                self.i2c.readfrom_into(self.ADDR, buf)
            finally:
                self.i2c.unlock()

            # 4. Enter sleep mode
            while not self.i2c.try_lock():
                pass
            try:
                self.i2c.writeto(self.ADDR, self.SLEEP)
            finally:
                self.i2c.unlock()

            # Verify CRC
            t_data = buf[0:2]
            t_crc = buf[2]
            h_data = buf[3:5]
            h_crc = buf[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 = (buf[0] << 8) | buf[1]
            raw_h = (buf[3] << 8) | buf[4]

            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:
                while not self.i2c.try_lock():
                    pass
                try:
                    self.i2c.writeto(self.ADDR, self.SLEEP)
                finally:
                    self.i2c.unlock()
            except:
                pass
            return None, None