'''
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.

A row is ALWAYS written each run, with a status byte (like data_NPM.npm_status
and data_NOISE.noise_status):
    s88_status = 0    -> OK, CO2 valid
    s88_status = 0xFF -> sensor not responding / read error (CO2 stored as 0)
This is essential: without it the table keeps the last good value forever and
loop/SARA_send_data_v2.py would keep transmitting a stale CO2 reading when the
sensor is actually dead.
'''

import serial
import sqlite3
import sys

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

STATUS_OK = 0x00
STATUS_NO_RESPONSE = 0xFF

# 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, timeout=10)
    cursor = conn.cursor()

    # Self-heal: ensure the table + status column exist even if create_db.py was
    # skipped during OTA. Duplicates the canonical schema from sqlite/create_db.py
    # — keep them in sync.
    cursor.execute("""
        CREATE TABLE IF NOT EXISTS data_S88 (
            timestamp TEXT,
            CO2 INTEGER,
            s88_status INTEGER DEFAULT 0
        )
    """)
    try:
        cursor.execute("ALTER TABLE data_S88 ADD COLUMN s88_status INTEGER DEFAULT 0")
    except Exception:
        pass  # Column already exists
    conn.commit()

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

    # Default to the error state; only a clean read flips it to OK.
    co2_ppm = 0
    status = STATUS_NO_RESPONSE

    ser = None
    try:
        ser = serial.Serial(
            port=port,
            baudrate=BAUDRATE,
            parity=serial.PARITY_NONE,
            stopbits=serial.STOPBITS_ONE,
            bytesize=serial.EIGHTBITS,
            timeout=1,
        )
        co2 = read_co2(ser)
        if co2 is not None:
            co2_ppm = int(round(co2))
            status = STATUS_OK
        else:
            print("S88 not responding -> writing error row (s88_status=0xFF)")
    except Exception as e:
        print(f"S88 serial/read error: {e} -> writing error row (s88_status=0xFF)")
    finally:
        if ser is not None:
            try:
                ser.close()
            except Exception:
                pass

    # ALWAYS write a row so the send loop never reuses a stale value.
    try:
        cursor.execute("SELECT last_updated FROM timestamp_table LIMIT 1")
        row = cursor.fetchone()
        rtc_time_str = row[0] if row else "not connected"

        cursor.execute(
            "INSERT INTO data_S88 (timestamp, CO2, s88_status) VALUES (?, ?, ?)",
            (rtc_time_str, co2_ppm, status),
        )
        conn.commit()

        if status == STATUS_OK:
            print(f"CO2: {co2_ppm} ppm (saved at {rtc_time_str})")
        else:
            print(f"S88 no data, s88_status=0x{status:02X} (saved at {rtc_time_str})")
    except Exception as e:
        print(f"S88 DB write error: {e}")
    finally:
        conn.close()


if __name__ == "__main__":
    main()