'''
Script to get CO2 values from Senseair S88 sensor and write to database
/usr/bin/python3 /var/www/nebuleair_pro_4g/S88/write_data.py

Modbus RTU 9600 8N1. Reads IR1..IR4 in one frame to get status + CO2.
If status (IR1) is non-zero the reading is skipped (warm-up or error).
'''

import serial
import sqlite3
import sys

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

# Modbus slave address: 0xFE = "any address", any S88 responds regardless of
# its configured individual address. Fine for single-sensor setups.
SLAVE_ADDR = 0xFE
# Read IR1..IR4 in one frame: function 0x04, start 0x0000, qty 0x0004
READ_REQUEST = bytes([SLAVE_ADDR, 0x04, 0x00, 0x00, 0x00, 0x04, 0xE5, 0xC6])
EXPECTED_RESPONSE_LEN = 13  # 1 addr + 1 fn + 1 count + 8 data + 2 CRC


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_config(cursor, key, default):
    cursor.execute("SELECT value FROM config_table WHERE key = ?", (key,))
    row = cursor.fetchone()
    return row[0] if row else default


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

    if len(response) < 5:
        print(f"S88: short response ({len(response)} bytes)")
        return None

    # Modbus exception response: function code has high bit set (0x84 instead of 0x04)
    if response[1] & 0x80:
        print(f"S88 Modbus exception: code={response[2]:#04x}")
        return None

    if len(response) != EXPECTED_RESPONSE_LEN:
        print(f"S88: unexpected response length {len(response)} (expected {EXPECTED_RESPONSE_LEN})")
        return None

    # Verify CRC (last two bytes, low byte first)
    received_crc = response[-2] | (response[-1] << 8)
    if crc16_modbus(response[:-2]) != received_crc:
        print("S88: CRC mismatch")
        return None

    if response[0] != SLAVE_ADDR or response[1] != 0x04 or response[2] != 0x08:
        print(f"S88: unexpected header {response[:3].hex()}")
        return None

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

    if status != 0:
        # DI8 = Warm Up (bit 7 of low byte). Other bits = errors.
        print(f"S88: sensor not ready, status={status:#06x}")
        return None

    return co2


def main():
    conn = sqlite3.connect(DB_PATH)
    cursor = conn.cursor()

    port = get_config(cursor, "S88_port", DEFAULT_PORT)

    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(f"Error opening serial port {port}: {e}")
        conn.close()
        sys.exit(1)

    try:
        co2 = read_co2(ser)
        if co2 is None:
            print("Failed to read CO2 from S88.")
            return

        co2_ppm = int(round(co2))

        cursor.execute("SELECT last_updated FROM timestamp_table LIMIT 1")
        row = cursor.fetchone()
        rtc_time_str = row[0]

        cursor.execute(
            "INSERT INTO data_S88 (timestamp, CO2) VALUES (?, ?)",
            (rtc_time_str, co2_ppm),
        )
        conn.commit()
        print(f"CO2: {co2_ppm} ppm (saved at {rtc_time_str})")
    except Exception as e:
        print(f"S88 error: {e}")
    finally:
        try:
            ser.close()
        except Exception:
            pass
        conn.close()


if __name__ == "__main__":
    main()