weatherstation-datacollector/test_pool_decode.py

#!/usr/bin/env python3
"""Test pool payload decoding with the new MQTT message format"""

import json
import struct
from typing import Optional, Tuple, Dict

PAYLOAD_SIZE = 15
MAGIC1 = 0x42
MAGIC2 = 0x99
RESET_FLAG_MAP = [
    (0x1, "PORF (power-on)"),
    (0x2, "EXTRF (external reset)"),
    (0x4, "BORF (brown-out)"),
    (0x8, "WDRF (watchdog)"),
]


def crc8_xor(data: bytes) -> int:
    """Simple XOR checksum used by the pool payload."""
    c = 0
    for b in data:
        c ^= b
    return c


def parse_version_and_reset_flags(version_byte: int):
    protocol_version = version_byte & 0x0F
    reset_flags = (version_byte >> 4) & 0x0F
    reset_causes = [desc for bit, desc in RESET_FLAG_MAP if reset_flags & bit]
    return protocol_version, reset_flags, reset_causes


def decode_pool_payload(candidate_bytes: bytes, expected_seq: Optional[int] = None):
    """Scan a byte stream for a plausible pool payload.

    Slides a 15-byte window, validates with CRC, version/nodeId, and range checks,
    and scores candidates. Returns the best decoded dict or None.
    """
    # Drop leading preamble (0xAA) if present
    while candidate_bytes.startswith(b"\xaa"):
        candidate_bytes = candidate_bytes[1:]

    best = None
    best_score = -1

    for offset in range(0, len(candidate_bytes) - PAYLOAD_SIZE + 1):
        chunk = candidate_bytes[offset:offset + PAYLOAD_SIZE]
        try:
            magic1, magic2, version_byte, nodeId, seq, t_ds10, t_bme10, hum10, pres1, crc_received = struct.unpack(
                '<BBBBHhhHHB', chunk
            )
        except struct.error:
            continue

        crc_calculated = crc8_xor(chunk[:-1])
        if crc_calculated != crc_received:
            continue

        protocol_version, reset_flags, reset_causes = parse_version_and_reset_flags(version_byte)

        if protocol_version != 1 or nodeId != 1:
            continue

        # Plausibility checks (unit scaled)
        if not (-300 <= t_ds10 <= 600):  # -30.0 to 60.0°C
            continue
        if not (-300 <= t_bme10 <= 600):
            continue
        if not (0 <= hum10 <= 1000):  # 0.0–100.0%
            continue
        if not (8000 <= pres1 <= 11000):  # 800.0–1100.0 hPa
            continue

        score = 0
        if magic1 == MAGIC1 and magic2 == MAGIC2:
            score += 2
        if expected_seq is not None and seq == expected_seq:
            score += 1
        # CRC already validated; reward shorter offset to prefer first valid
        score -= offset * 0.001

        if score > best_score:
            best_score = score
            best = {
                "offset": offset,
                "magic_ok": magic1 == MAGIC1 and magic2 == MAGIC2,
                "version": protocol_version,
                "version_byte": version_byte,
                "reset_flags": reset_flags,
                "reset_causes": reset_causes,
                "nodeId": nodeId,
                "sequence": seq,
                "t_ds_c": t_ds10 / 10.0,
                "t_bme_c": t_bme10 / 10.0,
                "humidity": hum10 / 10.0,
                "pressure_hpa": pres1 / 10.0,
                "crc_valid": True,
            }

    return best


def build_payload(seq: int, t_ds10: int, t_bme10: int, hum10: int, pres1: int, reset_flags: int = 0) -> bytes:
    """Build a valid payload with CRC appended."""
    version_byte = ((reset_flags & 0x0F) << 4) | 0x01
    header = struct.pack('<BBBBHhhHH', MAGIC1, MAGIC2, version_byte, 1, seq, t_ds10, t_bme10, hum10, pres1)
    crc = crc8_xor(header)
    return header + bytes([crc])


def extract_pool_candidate_bytes(raw_bytes: bytes) -> Tuple[bytes, Dict[str, str]]:
    """Mirror runtime extraction: strip 0xAA preamble and optional sync bytes."""
    trimmed = raw_bytes
    while trimmed.startswith(b"\xaa"):
        trimmed = trimmed[1:]

    for sync in (b"\x39\x14", b"\xd3\x91"):
        idx = trimmed.find(sync)
        if idx != -1 and idx + len(sync) < len(trimmed):
            return trimmed[idx + len(sync):], {"source": "sync", "offset": idx, "sync": sync.hex()}

    return trimmed, {"source": "raw"}


def demo_decode(hex_stream: str, label: str):
    print(f"\n--- {label} ---")
    byte_stream = bytes.fromhex(hex_stream)
    candidate_bytes, meta = extract_pool_candidate_bytes(byte_stream)
    print(f"candidate source={meta['source']}, len={len(candidate_bytes)}, hex={candidate_bytes.hex()}")
    decoded = decode_pool_payload(candidate_bytes)
    if decoded:
        print("✓ Decoded:")
        print(json.dumps(decoded, indent=2))
    else:
        print("✗ Failed to decode")


# Construct a known-good payload and embed it in the new frame layout (aa preamble + sync 0x39 0x14)
payload = build_payload(seq=0x013d, t_ds10=231, t_bme10=223, hum10=550, pres1=10123)
preamble = b"\xaa" * 8
sync = b"\x39\x14"
new_frame_hex = (preamble + sync + payload).hex()

# Legacy frame: just the payload bytes
legacy_hex = payload.hex()

print("Testing pool payload decoding for both hardware generations")
demo_decode(new_frame_hex, "New hardware (preamble + sync)")
demo_decode(legacy_hex, "Legacy hardware (bare payload)")