from machine import Pin, I2C
from time import sleep
import utime

# === LCD Setup ===
try:
    from lcd_api import LcdApi
    from i2c_lcd import I2cLcd
except ImportError:
    print("LCD libraries not found. Please install lcd_api and i2c_lcd.")
    raise

# Helper to pad/trim strings safely (MicroPython lacks str.ljust)
def pad16(text):
    """Return string padded/truncated to exactly 16 chars"""
    return (text + " " * 16)[:16]

# I²C at 100kHz (more reliable with PCF8574 backpacks)
i2c = I2C(0, sda=Pin(0), scl=Pin(1), freq=100000)

def init_lcd():
    sleep(0.05)  # 50 ms startup delay
    try:
        return I2cLcd(i2c, 0x27, 2, 16)  # Adjust I2C address if needed
    except Exception as e:
        print("LCD initialization failed. Check I2C address/wiring.")
        raise e

lcd = init_lcd()

# === Keypad Setup ===
ROWS = [Pin(i, Pin.OUT) for i in (2, 3, 4, 5)]
COLS = [Pin(i, Pin.IN, Pin.PULL_DOWN) for i in (6, 7, 8, 9)]

KEYS = [
    ['1', '2', '3', '+'],
    ['4', '5', '6', '-'],
    ['7', '8', '9', '*'],
    ['=', '0', '.', '/']
]

def scan_keypad():
    """Scan matrix and return key or None"""
    for row_num, row in enumerate(ROWS):
        row.high()
        for col_num, col in enumerate(COLS):
            if col.value():
                row.low()
                return KEYS[row_num][col_num]
        row.low()
    return None

# === Calculator State ===
first, second, operator, result = "", "", "", None
mode = "input_first"  # input_first → input_second → result_shown

def update_display():
    """Refresh LCD with current state"""
    lcd.move_to(0, 0)
    line = first
    if operator:
        line += f" {operator}"
    if second:
        line += f" {second}"
    lcd.putstr(pad16(line))

    if mode == "result_shown" and result is not None:
        lcd.move_to(0, 1)
        lcd.putstr(pad16(f"= {result}"))

def reset_state():
    """Reset calculator to idle"""
    global first, second, operator, result, mode
    first, second, operator, result = "", "", "", None
    mode = "input_first"
    lcd.move_to(0, 0)
    lcd.putstr(pad16("Goose Calc Ready"))
    lcd.move_to(0, 1)
    lcd.putstr(pad16(""))
    sleep(0.5)

def safe_calculate(first, operator, second):
    """Perform math operation safely"""
    try:
        a, b = float(first), float(second)
        if operator == '+': return a + b
        if operator == '-': return a - b
        if operator == '*': return a * b
        if operator == '/': return "Div by 0" if b == 0 else a / b
    except ValueError:
        return "Error"

def calculate():
    """Wrapper for safe calculation and display update"""
    global result, mode
    if not first or not operator or not second:
        result, mode = "Error", "result_shown"
        update_display()
        return

    value = safe_calculate(first, operator, second)
    if isinstance(value, (int, float)):
        if isinstance(value, float) and value % 1 == 0:
            result = str(int(value))  # Show 5.0 as "5"
        else:
            result = str(round(value, 8))  # Keep precision, strip junk
    else:
        result = str(value)

    mode = "result_shown"
    update_display()

def handle_key(key, press_duration):
    """Process key input with long-press clear"""
    global first, second, operator, result, mode

    # Long press '=' for clear
    if key == '=' and press_duration > 1000:
        reset_state()
        return

    # Numbers & decimal point
    if key.isdigit() or key == ".":
        if mode == "result_shown":
            first, second, operator, result, mode = "", "", "", None, "input_first"

        target = first if mode == "input_first" else second
        if key == ".":
            if "." in target: return
            if not target: target = "0"
        if len(target) < 10:
            target += key

        if mode == "input_first":
            first = target
        else:
            second = target

        update_display()

    # Operators
    elif key in "+-*/":
        if mode == "result_shown" and result not in ("Error", "Div by 0"):
            first, second, result, mode = result, "", None, "input_second"
        elif first and mode != "input_second":
            mode = "input_second"
        else:
            return
        operator = key
        update_display()

    # Equals
    elif key == "=" and operator and second:
        calculate()

# === Main Loop ===
reset_state()

last_key, last_key_time, press_start = None, 0, 0
debounce_ms = 150  # slightly faster than 200ms

while True:
    key = scan_keypad()
    current_time = utime.ticks_ms()

    if key and key != last_key and (current_time - last_key_time) > debounce_ms:
        press_start, last_key, last_key_time = current_time, key, current_time

    elif not key and last_key:
        press_duration = current_time - press_start
        handle_key(last_key, press_duration)
        last_key, last_key_time = None, current_time

    sleep(0.05)