from machine import Pin, Timer
from time import sleep

class Keypad:
    KEY_UP   = const(0)
    KEY_DOWN = const(1)
    keys = [['1', '2', '3', 'A'],
            ['4', '5', '6', 'B'],
            ['7', '8', '9', 'C'],
            ['*', '0', '#', 'D']]

    def __init__(self, rows, cols, bufferlenght=100):
        self.buffer = ''
        self.status = True
        self.bufferlenght = bufferlenght
        # Set pins for rows as outputs
        self.row_pins = [ Pin(pin_name, mode=Pin.OUT, value=0) for pin_name in rows ]
        # Set pins for columns as inputs
        self.col_pins = [ Pin(pin_name, mode=Pin.IN, pull=Pin.PULL_DOWN) for pin_name in cols ]
        Timer(freq=10, callback=self.pollKeypad)

    def pollKeypad(self, timer):
        key = None
        nokey = True
        for row in range(4):
            for col in range(4):
                # Set the current row to high
                self.row_pins[row].high()
                # Check for key pressed events
                if self.col_pins[col].value() == KEY_DOWN:
                    key = KEY_DOWN
                    nokey = False
                if self.col_pins[col].value() == KEY_UP:
                    key = KEY_UP
                self.row_pins[row].low()
                if key == KEY_DOWN and self.status:
                    self.buffer += self.keys[row][col]
                    self.status = False
                    if len(self.buffer)>self.bufferlenght:
                        self.buffer = self.buffer[-self.bufferlenght:]
        if nokey:
            self.status = True

    def clearBuffer(self):
        self.buffer = ''

    def getBuffer(self):
        return self.buffer

# Initialize and set all the rows to low
rows = [28, 27, 26, 22]
cols = [21, 20, 19, 18]
k = Keypad(rows=rows, cols=cols, bufferlenght=16)
oldtxt = ''
while True:
    newtxt = k.getBuffer()
    if len(newtxt)>0 and newtxt[-1] == '#':
        k.clearBuffer()
        newtxt = ''
    if newtxt != oldtxt:
        print(newtxt)
        oldtxt = newtxt
    sleep(.1)