# ammb/protocol.py
"""
Defines handlers for different **Serial** communication protocols.

Allows the bridge (specifically the MeshcoreHandler) to encode/decode
messages based on the serial protocol specified in the configuration.

Includes:
- JsonNewlineProtocol: For text-based JSON (default).
- RawSerialProtocol: For binary/companion modes (fallback).
"""

import json
import logging
import binascii
from abc import ABC, abstractmethod
from typing import Dict, Optional, Any

# --- Base Class ---
class MeshcoreProtocolHandler(ABC):
    """
    Abstract base class for handling **Serial** protocols for the external device.
    """
    def __init__(self):
        # Get logger named after the specific subclass implementing the protocol
        self.logger = logging.getLogger(f"{__name__}.{self.__class__.__name__}")
        self.logger.debug("Serial protocol handler initialized.")

    @abstractmethod
    def read(self, serial_port) -> Optional[bytes]:
        """
        Reads data from the serial port according to the protocol's needs.
        Returns bytes read, or None.
        """
        pass

    @abstractmethod
    def encode(self, data: Dict[str, Any]) -> Optional[bytes]:
        """Encodes a dictionary payload into bytes suitable for sending over serial."""
        pass

    @abstractmethod
    def decode(self, raw_data: bytes) -> Optional[Dict[str, Any]]:
        """Decodes bytes received from serial into a dictionary."""
        pass

# --- Concrete Implementations ---

class JsonNewlineProtocol(MeshcoreProtocolHandler):
    """
    Handles newline-terminated JSON strings encoded in UTF-8 over **Serial**.
    """
    def read(self, serial_port) -> Optional[bytes]:
        """Reads a single line ending in \\n."""
        if serial_port.in_waiting > 0:
            return serial_port.readline()
        return None

    def encode(self, data: Dict[str, Any]) -> Optional[bytes]:
        try:
            encoded_message = json.dumps(data).encode('utf-8') + b'\n'
            self.logger.debug(f"Encoded: {encoded_message!r}")
            return encoded_message
        except (TypeError, ValueError) as e:
            self.logger.error(f"JSON Encode Error: {e} - Data: {data}", exc_info=True)
            return None
        except Exception as e:
            self.logger.error(f"Unexpected serial encoding error: {e}", exc_info=True)
            return None

    def decode(self, raw_data: bytes) -> Optional[Dict[str, Any]]:
        try:
            decoded_str = raw_data.decode('utf-8', errors='replace').strip()
            if not decoded_str:
                return None
            
            decoded_data = json.loads(decoded_str)
            if not isinstance(decoded_data, dict):
                 self.logger.warning(f"Decoded JSON is not a dictionary: {decoded_str!r}")
                 return None
            return decoded_data
        except json.JSONDecodeError:
            self.logger.warning(f"Received non-JSON data or incomplete JSON line: {raw_data!r}")
            return None
        except Exception as e:
            self.logger.error(f"Error decoding serial data: {e} - Raw: {raw_data!r}")
            return None


class RawSerialProtocol(MeshcoreProtocolHandler):
    """
    Handles RAW Binary data from the serial port. Use for 'Companion USB Mode'.
    """
    def read(self, serial_port) -> Optional[bytes]:
        """Reads all currently available bytes from the buffer."""
        if serial_port.in_waiting > 0:
            return serial_port.read(serial_port.in_waiting)
        return None

    def encode(self, data: Dict[str, Any]) -> Optional[bytes]:
        """Encodes outgoing data."""
        try:
            payload = data.get('payload', '')
            if isinstance(payload, str):
                return payload.encode('utf-8')
            elif isinstance(payload, (bytes, bytearray)):
                return payload
            return None
        except Exception as e:
            self.logger.error(f"Error encoding raw data: {e}")
            return None

    def decode(self, raw_data: bytes) -> Optional[Dict[str, Any]]:
        """Wraps received raw bytes into a bridge-compatible dictionary."""
        if not raw_data:
            return None
            
        try:
            hex_str = binascii.hexlify(raw_data).decode('ascii')
            return {
                "destination_meshtastic_id": "^all", 
                "payload": f"MC_BIN: {hex_str}",
                "raw_binary": True
            }
        except Exception as e:
            self.logger.error(f"Error processing raw binary: {e}")
            return None

# --- Factory Function ---

_serial_protocol_handlers = {
    'json_newline': JsonNewlineProtocol,
    'raw_serial': RawSerialProtocol,
}

def get_serial_protocol_handler(protocol_name: str) -> MeshcoreProtocolHandler:
    """Factory function to get an instance of the appropriate **Serial** protocol handler."""
    logger = logging.getLogger(__name__)
    protocol_name_lower = protocol_name.lower()
    handler_class = _serial_protocol_handlers.get(protocol_name_lower)

    if handler_class:
        logger.info(f"Using Serial protocol handler: {handler_class.__name__}")
        return handler_class()
    else:
        logger.error(f"Unsupported Serial protocol: '{protocol_name}'. Available: {list(_serial_protocol_handlers.keys())}")
        raise ValueError(f"Unsupported Serial protocol: {protocol_name}")