nebuleair_pro_4g/CCS811/daemon.py

'''
Long-running daemon for the AMS CCS811 air-quality sensor (TVOC + eCO2).
Run by systemd nebuleair-ccs811-data.service (Type=simple, Restart=always).

WHY a daemon and not a 10s oneshot timer like the other sensors:
the CCS811 must be initialised ONCE and then read continuously. Each driver
(re)init does a reset + app_start, and the first samples right after that are
garbage (eCO2 = 0 or 0x8000+ corruption). Resetting every 10s also prevents the
sensor's baseline algorithm from ever building up. So we init once here and loop.

Valid eCO2 range is [400, 8192] ppm. Out-of-range samples (notably 0x8000 = 32768,
an I2C clock-stretching corruption artifact on the Pi) are dropped.

TVOC is the primary measurement; eCO2 is *derived* from VOCs (not a true NDIR CO2).

The web "Get Data" button does NOT read the sensor (that would collide with this
daemon on the I2C bus and corrupt it) — it reads the last row from the DB instead.
See CCS811/get_data.py.
'''

import sqlite3
import sys
import time

DB_PATH = "/var/www/nebuleair_pro_4g/sqlite/sensors.db"
DEFAULT_ADDRESS = 0x5A
READ_INTERVAL = 10        # seconds between stored samples
ECO2_MIN, ECO2_MAX = 400, 8192   # CCS811 physical eCO2 range
SAMPLE_TIMEOUT = 4        # max seconds to wait for a valid sample within a tick
REINIT_AFTER_ERRORS = 5   # consecutive I2C errors before re-initialising the sensor
INIT_RETRY_DELAY = 10     # seconds between init attempts


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 ensure_table(cursor):
    # Self-heal: duplicates the canonical schema from sqlite/create_db.py.
    cursor.execute("""
        CREATE TABLE IF NOT EXISTS data_CCS811 (
            timestamp TEXT,
            eCO2 INTEGER,
            TVOC INTEGER
        )
    """)


def init_sensor(address):
    import board
    import busio
    import adafruit_ccs811
    i2c = busio.I2C(board.SCL, board.SDA)
    return adafruit_ccs811.CCS811(i2c, address=address)


def init_with_retry(address):
    while True:
        try:
            ccs = init_sensor(address)
            print(f"CCS811: initialised at {hex(address)}", flush=True)
            return ccs
        except Exception as e:
            print(f"CCS811: init failed at {hex(address)}: {e} (retry in {INIT_RETRY_DELAY}s)", flush=True)
            time.sleep(INIT_RETRY_DELAY)


def read_valid_sample(ccs):
    '''Poll up to SAMPLE_TIMEOUT for a data_ready sample in the valid eCO2 range.
    Returns (eco2, tvoc) or None. Raises OSError on I2C failure.'''
    end = time.monotonic() + SAMPLE_TIMEOUT
    while time.monotonic() < end:
        if ccs.data_ready:
            eco2 = int(ccs.eco2)
            tvoc = int(ccs.tvoc)
            if ECO2_MIN <= eco2 <= ECO2_MAX:
                return eco2, tvoc
            # else: out-of-range (warm-up 0 or 0x8000 corruption) -> keep polling
        time.sleep(0.5)
    return None


def main():
    conn = sqlite3.connect(DB_PATH, timeout=10)
    cursor = conn.cursor()
    ensure_table(cursor)
    conn.commit()

    addr_str = get_config(cursor, "CCS811_address", "0x5A")
    try:
        address = int(str(addr_str), 16)
    except ValueError:
        address = DEFAULT_ADDRESS

    try:
        import board  # noqa: F401
        import busio  # noqa: F401
        import adafruit_ccs811  # noqa: F401
    except Exception as e:
        print(f"CCS811: library import failed: {e}", flush=True)
        conn.close()
        sys.exit(1)

    ccs = init_with_retry(address)
    print("CCS811: discarding warm-up samples...", flush=True)

    consecutive_errors = 0
    while True:
        try:
            sample = read_valid_sample(ccs)
            consecutive_errors = 0

            if sample is None:
                print("CCS811: no valid sample this tick (warming up or corrupted), skipping.", flush=True)
            else:
                eco2, tvoc = sample
                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_CCS811 (timestamp, eCO2, TVOC) VALUES (?, ?, ?)",
                    (rtc_time_str, eco2, tvoc),
                )
                conn.commit()
                print(f"eCO2: {eco2} ppm, TVOC: {tvoc} ppb (saved at {rtc_time_str})", flush=True)

        except OSError as e:
            consecutive_errors += 1
            print(f"CCS811: I2C error: {e} (#{consecutive_errors})", flush=True)
            if consecutive_errors >= REINIT_AFTER_ERRORS:
                print("CCS811: too many I2C errors, re-initialising sensor...", flush=True)
                ccs = init_with_retry(address)
                consecutive_errors = 0
        except Exception as e:
            print(f"CCS811: unexpected error: {e}", flush=True)

        time.sleep(READ_INTERVAL)


if __name__ == "__main__":
    main()