"""
==========================================================
  4x4 Keypad Calculator — Raspberry Pi Pico (MicroPython)
  LCD  SDA -> GP4   SCL -> GP2   (I2C addr 0x27)
  Keypad rows -> GP10-GP13  |  cols -> GP14-GP17
  Layout:  1 2 3 /
           4 5 6 *
           7 8 9 -
           . 0 = +
==========================================================
"""

from machine import Pin, SoftI2C
import time

# ── helpers ────────────────────────────────────────────────────────────────
def pad(text, width=16):
    """MicroPython-safe left-justify: pad with spaces to `width`."""
    s = str(text)[:width]
    while len(s) < width:
        s += " "
    return s

# ── I2C LCD driver (PCF8574 backpack) ──────────────────────────────────────
class I2cLcd:
    LCD_CHR    = 1
    LCD_CMD    = 0
    LCD_LINE_1 = 0x80
    LCD_LINE_2 = 0xC0
    LCD_BL     = 0x08
    ENABLE     = 0b00000100

    def __init__(self, i2c, addr=0x27):
        self.i2c  = i2c
        self.addr = addr
        self.buf  = bytearray(1)
        time.sleep_ms(50)
        self._write4(0x03); time.sleep_ms(5)
        self._write4(0x03); time.sleep_ms(1)
        self._write4(0x03)
        self._write4(0x02)
        self.send(0x28, self.LCD_CMD)   # 4-bit, 2 lines
        self.send(0x0C, self.LCD_CMD)   # display on, cursor off
        self.send(0x06, self.LCD_CMD)   # entry: increment
        self.clear()

    def _strobe(self, data):
        self.buf[0] = data | self.ENABLE | self.LCD_BL
        self.i2c.writeto(self.addr, self.buf)
        time.sleep_us(500)
        self.buf[0] = (data & ~self.ENABLE) | self.LCD_BL
        self.i2c.writeto(self.addr, self.buf)
        time.sleep_us(100)

    def _write4(self, data):
        b = (data << 4) | self.LCD_BL
        self.buf[0] = b
        self.i2c.writeto(self.addr, self.buf)
        self._strobe(b)

    def send(self, data, mode):
        hi = mode | (data & 0xF0)        | self.LCD_BL
        lo = mode | ((data << 4) & 0xF0) | self.LCD_BL
        self.i2c.writeto(self.addr, bytes([hi])); self._strobe(hi)
        self.i2c.writeto(self.addr, bytes([lo])); self._strobe(lo)

    def clear(self):
        self.send(0x01, self.LCD_CMD)
        time.sleep_ms(3)

    def move(self, row, col):
        self.send([self.LCD_LINE_1, self.LCD_LINE_2][row] + col, self.LCD_CMD)

    def write(self, text):
        for ch in str(text):
            self.send(ord(ch), self.LCD_CHR)

    def print_line(self, row, text):
        """Write exactly 16 chars on a row (no ljust needed)."""
        self.move(row, 0)
        self.write(pad(text, 16))


# ── Keypad driver ──────────────────────────────────────────────────────────
class Keypad:
    def __init__(self, row_pins, col_pins, layout):
        self.rows   = [Pin(p, Pin.OUT) for p in row_pins]
        self.cols   = [Pin(p, Pin.IN, Pin.PULL_DOWN) for p in col_pins]
        self.layout = layout

    def scan(self):
        for r, rp in enumerate(self.rows):
            rp.high()
            for c, cp in enumerate(self.cols):
                if cp.value():
                    rp.low()
                    return self.layout[r][c]
            rp.low()
        return None


# ── Safe eval ──────────────────────────────────────────────────────────────
def safe_eval(expr):
    allowed = set("0123456789.+-*/()")
    if not all(ch in allowed for ch in expr):
        return None, "Bad input"
    try:
        result = eval(expr)
        if isinstance(result, float):
            if result == int(result) and abs(result) < 1e12:
                result = int(result)
            else:
                result = float('{:.6g}'.format(result))
        return result, None
    except ZeroDivisionError:
        return None, "Div by 0!"
    except Exception:
        return None, "Syntax Err"


# ── Hardware init ──────────────────────────────────────────────────────────
i2c = SoftI2C(sda=Pin(4), scl=Pin(2), freq=100_000)   # SDA=GP4, SCL=GP2
lcd = I2cLcd(i2c, addr=0x27)

LAYOUT = [
    ['1', '2', '3', '/'],
    ['4', '5', '6', '*'],
    ['7', '8', '9', '-'],
    ['.', '0', '=', '+'],
]
keypad = Keypad(
    row_pins=[10, 11, 12, 13],
    col_pins=[14, 15, 16, 17],
    layout=LAYOUT
)

# ── State ──────────────────────────────────────────────────────────────────
expression  = ""
last_key    = None
just_evaled = False
MAX_EXPR    = 32

# ── Boot splash ────────────────────────────────────────────────────────────
lcd.print_line(0, "  Pi Calculator ")
lcd.print_line(1, "  Ready...      ")
time.sleep(1)
lcd.print_line(0, "")
lcd.print_line(1, "")


# ── Display helpers ────────────────────────────────────────────────────────
def refresh():
    lcd.print_line(0, expression[-16:] if expression else "")
    lcd.print_line(1, "")

def show_result(expr, result):
    lcd.print_line(0, expr[-16:])
    lcd.print_line(1, "= " + str(result))

def show_error(msg):
    lcd.print_line(0, "    ERROR!      ")
    lcd.print_line(1, msg)


# ── Main loop ──────────────────────────────────────────────────────────────
while True:
    key = keypad.scan()

    if key and key != last_key:
        last_key = key

        if key == '=':
            if expression:
                result, err = safe_eval(expression)
                if err:
                    show_error(err)
                    expression  = ""
                    just_evaled = False
                else:
                    show_result(expression, result)
                    expression  = str(result)
                    just_evaled = True

        else:
            if just_evaled:
                expression  = expression + key if key in '+-*/' else key
                just_evaled = False
            else:
                if key in '+-*/' and expression and expression[-1] in '+-*/':
                    expression = expression[:-1] + key
                else:
                    expression += key

            if len(expression) > MAX_EXPR:
                expression = expression[:MAX_EXPR]

            refresh()

    elif not key:
        last_key = None

    time.sleep_ms(50)