from machine import Pin
import sys

class Encoder:
    _increment_grid = [[0, -1, 1, None],
                       [1, 0, None, -1],
                       [-1, None, 0, 1],
                       [None, 1, -1, 0]]

    @property
    def total_change(self):
        return self._total_change

    def __init__(self, channel_a, channel_b):
        self.channel_a = self._configure_channel(channel_a)
        self.channel_b = self._configure_channel(channel_b)
        self.reset()

    def reset(self):
        self._previous_value = None
        self._total_change = 0

    def _irq_cb(self, input_pin):
        print('IRQ handler called')
        current_value = (self.channel_a.value() * 2) + self.channel_b.value()
        if self._previous_value == None:
            self._previous_value = current_value
            return
        try:
            change_amount = self._increment_grid[self._previous_value][current_value]
            self._total_change += change_amount
        except TypeError:
            print('Detected invalid encoder state! Can the system keep up?', file=sys.stderr)
        self._previous_value = current_value

    def _configure_channel(self, pin):
        p = pin if isinstance(pin, Pin) else Pin(pin, Pin.IN, pull=Pin.PULL_UP)
        p.irq(self._irq_cb, trigger=(Pin.IRQ_FALLING | Pin.IRQ_RISING))
        return p