SwapStation_WebApp/backend/core/protobuf_decoder.py

import json
from google.protobuf.json_format import MessageToDict
from google.protobuf.message import DecodeError

# Import the specific message types from your generated protobuf file
# Make sure the path 'proto.your_proto_file_pb2' matches your file structure
from proto.vec_payload_chgSt_pb2 import (
    mainPayload as PeriodicData, 
    eventPayload as EventData, 
    rpcRequest as RpcRequest,
    eventType_e,
    jobType_e,
    languageType_e
)

class ProtobufDecoder:
    """
    Handles the decoding of different Protobuf message types with robust error handling.
    """

    def decode_periodic(self, payload: bytes) -> dict | None:
        """
        Decodes a binary payload into a PeriodicData dictionary.
        """
        try:
            message = PeriodicData()
            message.ParseFromString(payload)
            return MessageToDict(message, preserving_proto_field_name=True)
        except DecodeError as e:
            print(f"Error decoding PeriodicData: {e}")
            return None
        except Exception as e:
            print(f"An unexpected error occurred during periodic decoding: {e}")
            return None

    def decode_event(self, payload_bytes: bytes) -> dict | None:
        """
        Decodes an event payload robustly, ensuring the correct eventType is used.
        """
        try:
            # 1. Standard parsing to get a base dictionary
            msg = EventData()
            msg.ParseFromString(payload_bytes)
            d = MessageToDict(msg, preserving_proto_field_name=True)

            # 2. Manually extract the true enum value from the raw bytes
            wire_num = self._extract_field3_varint(payload_bytes)
            wire_name = None
            if wire_num is not None:
                try:
                    wire_name = eventType_e.Name(wire_num)
                except ValueError:
                    wire_name = f"UNKNOWN_ENUM_VALUE_{wire_num}"
            
            # 3. Always prefer the manually extracted "wire value"
            if wire_name:
                d["eventType"] = wire_name

            # 4. Ensure consistent structure with default values
            ed = d.setdefault("eventData", {})
            ed.setdefault("nfcData", None)
            ed.setdefault("batteryIdentification", "")
            ed.setdefault("activityFailureReason", 0)
            ed.setdefault("swapAbortReason", "ABORT_UNKNOWN")
            ed.setdefault("swapTime", 0)
            ed.setdefault("faultCode", 0)
            ed.setdefault("doorStatus", 0)
            ed.setdefault("slotId", 0)
            
            # 5. Reorder for clean logs and return as a dictionary
            return {
                "ts": d.get("ts"),
                "deviceId": d.get("deviceId"),
                "eventType": d.get("eventType"),
                "sessionId": d.get("sessionId"),
                "eventData": d.get("eventData"),
            }
        except Exception as e:
            print(f"An unexpected error occurred during event decoding: {e}")
            return None

    def decode_rpc_request(self, payload_bytes: bytes) -> dict | None:
        """
        Decodes an RPC request payload robustly, ensuring the correct jobType is used.
        """
        try:
            # 1. Standard parsing
            msg = RpcRequest()
            msg.ParseFromString(payload_bytes)
            d = MessageToDict(msg, preserving_proto_field_name=True)

            # 2. Manually extract the true enum value for jobType (field 3)
            wire_num = self._extract_field3_varint(payload_bytes)
            wire_name = None
            if wire_num is not None:
                try:
                    wire_name = jobType_e.Name(wire_num)
                except ValueError:
                    wire_name = f"UNKNOWN_ENUM_VALUE_{wire_num}"
            
            # 3. Prefer the manually extracted value
            if wire_name:
                d["jobType"] = wire_name

            # 4. Ensure consistent structure
            d.setdefault("rpcData", None)
            d.setdefault("slotInfo", None)
            
            return d
        except Exception as e:
            print(f"An unexpected error occurred during RPC request decoding: {e}")
            return None


    # --- Helper methods for manual byte parsing ---
    def _read_varint(self, b: bytes, i: int):
        """Helper to read a varint from a raw byte buffer."""
        shift = 0
        val = 0
        while True:
            if i >= len(b): raise ValueError("truncated varint")
            c = b[i]
            i += 1
            val |= (c & 0x7F) << shift
            if not (c & 0x80): break
            shift += 7
            if shift > 64: raise ValueError("varint too long")
        return val, i

    def _skip_field(self, b: bytes, i: int, wt: int):
        """Helper to skip a field in the buffer based on its wire type."""
        if wt == 0:  # VARINT
            _, i = self._read_varint(b, i)
            return i
        if wt == 1:  # 64-BIT
            return i + 8
        if wt == 2:  # LENGTH-DELIMITED
            ln, i = self._read_varint(b, i)
            return i + ln
        if wt == 5:  # 32-BIT
            return i + 4
        raise ValueError(f"unsupported wire type to skip: {wt}")

    def _extract_field3_varint(self, b: bytes):
        """Manually parses the byte string to find the integer value of field number 3 (e.g., eventType, jobType)."""
        i = 0
        n = len(b)
        while i < n:
            key, i2 = self._read_varint(b, i)
            wt = key & 0x7
            fn = key >> 3
            i = i2
            if fn == 3 and wt == 0:
                v, _ = self._read_varint(b, i)
                return v
            i = self._skip_field(b, i, wt)
        return None