import re
from abc import ABC, abstractmethod
from dataclasses import dataclass, field
from typing import List

SAFE_ID = re.compile(r"^[a-zA-Z0-9._-]")


def sanitize_id(value: str, fallback:str) -> str:
    """Sanitize a string to be used as an ID by removing unsafe characters."""
    return SAFE_ID.sub("_", value) or fallback


@dataclass
class Session:
    """Conversasion history for one (user_id, session_id) pair.
    ``message`` is in Strands / Bedrock-converse format (provider-neutral::
        {"role": "user"|"assistant"|"system",
         "content": [{"text": ...} | {"toolUse": ...} | {"toolResult": ...} ]})
    """
    session_id: str
    user_id: str
    messages: List[dict] = field(default_factory=list)
    

class SessionStore(ABC):
    """Abstract base class for session storage backends."""

    @abstractmethod
    def load(self, user_id: str, session_id: str) -> Session:
        """Return prior history for the key (empty Session if none exists yet)."""
        pass

    @abstractmethod
    def save(self, session: Session) -> None:
        """Save a session to the store."""
        pass
    
    @abstractmethod
    def clear(self, user_id: str, session_id: str) -> None:
        """Clear a session from the store."""
        pass