import array

import micropython
import utime
import machine
from micropython import const


class InvalidChecksum(Exception):
    pass


class InvalidPulseCount(Exception):
    pass


MAX_UNCHANGED = const(100)
MIN_INTERVAL_US = const(200000)
HIGH_LEVEL = const(50)
EXPECTED_PULSES = const(84)


class Pin(object):
    _temperature: float
    _humidity: float

    def __init__(self, pinn):
        self._pin = machine.Pin(pinn, machine.Pin.OUT, machine.Pin.PULL_DOWN)
        self._last_measure = utime.ticks_us()
        self._temperature = -1
        self._humidity = -1

    def measure(self):
        current_ticks = utime.ticks_us()
        if utime.ticks_diff(current_ticks, self._last_measure) < MIN_INTERVAL_US and (
            self._temperature > -1 or self._humidity > -1
        ):
            # Less than a second since last read, which is too soon according
            # to the datasheet
            return

        self._send_init_signal()
        pulses = self._capture_pulses()
        buffer = self._convert_pulses_to_buffer(pulses)
        #self._verify_checksum(buffer)

        self._humidity = buffer[0] + buffer[1] / 10
        self._temperature = buffer[2] + buffer[3] / 10
        self._last_measure = utime.ticks_us()

    @property
    def humi(self):
        try:
            self.measure()
            return self._humidity
        except:
            pass

    @property
    def temp(self):
        try:
            self.measure()
            return self._temperature
        except:
            pass

    def _send_init_signal(self):
        self._pin.init(machine.Pin.OUT, machine.Pin.PULL_DOWN)
        self._pin.value(1)
        utime.sleep_ms(50)
        self._pin.value(0)
        utime.sleep_ms(18)

    @micropython.native
    def _capture_pulses(self):
        pin = self._pin
        pin.init(machine.Pin.IN, machine.Pin.PULL_UP)

        val = 1
        idx = 0
        transitions = bytearray(EXPECTED_PULSES)
        unchanged = 0
        timestamp = utime.ticks_us()

        while unchanged < MAX_UNCHANGED:
            if val != pin.value():
                if idx >= EXPECTED_PULSES:
                    raise InvalidPulseCount(
                        "Got more than {} pulses".format(EXPECTED_PULSES)
                    )
                now = utime.ticks_us()
                transitions[idx] = now - timestamp
                timestamp = now
                idx += 1

                val = 1 - val
                unchanged = 0
            else:
                unchanged += 1
        pin.init(machine.Pin.OUT, machine.Pin.PULL_DOWN)
        if idx != EXPECTED_PULSES:
            raise InvalidPulseCount(
                "Expected {} but got {} pulses".format(EXPECTED_PULSES, idx)
            )
        return transitions[4:]

    def _convert_pulses_to_buffer(self, pulses):
        """Convert a list of 80 pulses into a 5 byte buffer
        The resulting 5 bytes in the buffer will be:
            0: Integral relative humidity data
            1: Decimal relative humidity data
            2: Integral temperature data
            3: Decimal temperature data
            4: Checksum
        """
        # Convert the pulses to 40 bits
        binary = 0
        for idx in range(0, len(pulses), 2):
            binary = binary << 1 | int(pulses[idx] > HIGH_LEVEL)

        # Split into 5 bytes
        buffer = array.array("B")
        for shift in range(4, -1, -1):
            buffer.append(binary >> shift * 8 & 0xFF)
        return buffer

    def _verify_checksum(self, buffer):
        # Calculate checksum
        checksum = 0
        for buf in buffer[0:4]:
            checksum += buf
        if checksum & 0xFF != buffer[4]:
            raise InvalidChecksum()