'''
Live read of the Senseair S88 CO2 sensor (used by the web "Get Data" button).
Prints a JSON object: {"CO2": <int_ppm>} or {"error": "<message>"}.

Modbus RTU 9600 8N1, reads IR1..IR4 in one frame.

Usage: /usr/bin/python3 /var/www/nebuleair_pro_4g/S88/get_data.py [port]
If no port is given, the script reads S88_port from config_table.
'''

import json
import sqlite3
import sys

import serial

DB_PATH = "/var/www/nebuleair_pro_4g/sqlite/sensors.db"
DEFAULT_PORT = "/dev/ttyAMA5"
BAUDRATE = 9600

SLAVE_ADDR = 0xFE
READ_REQUEST = bytes([SLAVE_ADDR, 0x04, 0x00, 0x00, 0x00, 0x04, 0xE5, 0xC6])
EXPECTED_RESPONSE_LEN = 13


def crc16_modbus(data):
    crc = 0xFFFF
    for byte in data:
        crc ^= byte
        for _ in range(8):
            if crc & 1:
                crc = (crc >> 1) ^ 0xA001
            else:
                crc >>= 1
    return crc


def get_port_from_config():
    try:
        conn = sqlite3.connect(DB_PATH)
        cursor = conn.cursor()
        cursor.execute("SELECT value FROM config_table WHERE key = ?", ("S88_port",))
        row = cursor.fetchone()
        conn.close()
        return row[0] if row else DEFAULT_PORT
    except Exception:
        return DEFAULT_PORT


def read_co2(ser):
    ser.reset_input_buffer()
    ser.write(READ_REQUEST)
    response = ser.read(EXPECTED_RESPONSE_LEN)

    if len(response) < 5:
        return None, f"short response ({len(response)} bytes)"

    if response[1] & 0x80:
        return None, f"Modbus exception code {response[2]:#04x}"

    if len(response) != EXPECTED_RESPONSE_LEN:
        return None, f"unexpected response length {len(response)}"

    received_crc = response[-2] | (response[-1] << 8)
    if crc16_modbus(response[:-2]) != received_crc:
        return None, "CRC mismatch"

    if response[0] != SLAVE_ADDR or response[1] != 0x04 or response[2] != 0x08:
        return None, f"unexpected header {response[:3].hex()}"

    status = (response[3] << 8) | response[4]
    co2 = (response[9] << 8) | response[10]

    if status != 0:
        return None, f"sensor not ready (status={status:#06x})"

    return co2, None


def main():
    port = sys.argv[1] if len(sys.argv) > 1 else get_port_from_config()

    try:
        ser = serial.Serial(
            port=port,
            baudrate=BAUDRATE,
            parity=serial.PARITY_NONE,
            stopbits=serial.STOPBITS_ONE,
            bytesize=serial.EIGHTBITS,
            timeout=1,
        )
    except Exception as e:
        print(json.dumps({"error": f"Cannot open {port}: {e}"}))
        return

    try:
        co2, err = read_co2(ser)
        if co2 is None:
            print(json.dumps({"error": err or "No data from S88"}))
            return
        print(json.dumps({"CO2": int(round(co2))}))
    except Exception as e:
        print(json.dumps({"error": f"S88 read error: {e}"}))
    finally:
        try:
            ser.close()
        except Exception:
            pass


if __name__ == "__main__":
    main()