#!/usr/bin/env python3
"""
GPIO‑monitor.py

* Sets every usable BCM pin as an input (pull‑down default)
* Saves the last read state of each pin
* In an infinite loop it polls the pins (≈10 ms per pass)
* When one or more pins change it prints:
      - Which pins changed and old→new values
      - The full 32‑bit snapshot as a binary string (MSB = highest pin)

Run as root (or a user in the *gpio* group):
    sudo python3 GPIO‑monitor.py
Press Ctrl‑C to stop – the script cleans up the GPIO pins.
"""

import sys
import time
import signal
import RPi.GPIO as GPIO

# ----------------------------------------------------------------------
# 1️⃣  Pin list – all BCM pins that exist on the 40‑pin header
# ----------------------------------------------------------------------
GPIO_PINS = [
    2, 3, 4, 5, 6, 7, 8, 9,
    10, 11, 12, 13, 14, 15, 16, 17,
    18, 19, 20, 21, 22, 23, 24, 25,
    26, 27
]

# ----------------------------------------------------------------------
# 2️⃣  Initialise GPIO
# ----------------------------------------------------------------------
GPIO.setmode(GPIO.BCM)

# keep only those pins we can actually configure
active_pins = []
failed = []

for pin in GPIO_PINS:
    try:
        GPIO.setup(pin, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
        active_pins.append(pin)
    except Exception as e:
        failed.append((pin, str(e)))

if failed:
    sys.stderr.write("⚠️  Could not initialise the following pins (they will be ignored):\n")
    for p, msg in failed:
        sys.stderr.write(f"    Pin {p}: {msg}\n")

# ----------------------------------------------------------------------
# 3️⃣  Helper to read the current snapshot (dict pin→0/1)
# ----------------------------------------------------------------------
def read_all():
    return {pin: GPIO.input(pin) for pin in active_pins}

# ----------------------------------------------------------------------
# 4️⃣  Signal handling – graceful exit on Ctrl‑C / SIGTERM
# ----------------------------------------------------------------------
keep_running = True

def _handle_exit(signum, frame):
    global keep_running
    keep_running = False

signal.signal(signal.SIGINT,  _handle_exit)   # Ctrl‑C
signal.signal(signal.SIGTERM, _handle_exit)

# ----------------------------------------------------------------------
# 5️⃣  Main monitoring loop
# ----------------------------------------------------------------------
prev_state = read_all()        # initial snapshot

print("🔎 Monitoring {} GPIO pins – press Ctrl‑C to stop".format(len(active_pins)))
while keep_running:
    cur_state = read_all()

    # Find pins whose value differed from the previous snapshot
    changed = [(pin, prev_state[pin], cur_state[pin])
               for pin in active_pins
               if prev_state[pin] != cur_state[pin]]

    if changed:
        # Build a readable change list  e.g. "4:0→1, 17:1→0"
        changes_txt = ", ".join(f"{pin}:{old}→{new}" for pin, old, new in changed)

        # Build a compact binary view – 32‑bit with pins sorted ascending
        # (higher pins become more significant bits)
        bits = "".join(str(cur_state[p]) for p in sorted(active_pins, reverse=True))
        # Pad to a multiple of 4 for readability
        pad_len = (4 - len(bits) % 4) % 4
        bits = "0" * pad_len + bits

        print(f"[{time.strftime('%H:%M:%S')}] Change detected – {changes_txt}")
        print(f"    Current snapshot: 0b{bits}")

        # Update reference for the next iteration
        prev_state = cur_state

    # Polling interval – adjust if you need faster/slower response
    time.sleep(0.01)   # 10 ms

# ----------------------------------------------------------------------
# 6️⃣  Cleanup
# ----------------------------------------------------------------------
GPIO.cleanup()
print("\n✅ Monitoring stopped – GPIO pins released.")