app/services/session_core/manager.py

"""Author RAG Chatbot SaaS — Session Memory Manager.

Redis-backed conversation memory: stores last N turns per session.
Interest profiler: accumulates topic tags across turns.
RULE: Session TTL resets on every message — 30 min inactivity = expire.
RULE: Interest profile is anonymous — no PII ever stored in Redis.
"""

import json
from dataclasses import dataclass, field
from datetime import timedelta

import structlog
from redis.asyncio import Redis

from app.config import get_settings
from app.services.session_core.context import extract_interest_tags, compute_interest_score

logger = structlog.get_logger(__name__)
cfg = get_settings()

_SESSION_PREFIX = "session:"
_INTEREST_PREFIX = "interest:"
_HISTORY_KEY = "history"
_BOOK_KEY = "selected_book"
_TURN_KEY = "turn_count"


@dataclass
class SessionContext:
    """Full context for a chat session turn."""

    session_id: str
    author_id: str
    history: list[dict] = field(default_factory=list)          # Last N turns [{role, content}]
    selected_book_id: str | None = None                         # Currently selected book
    is_cross_book: bool = False                                  # Searching all books
    turn_count: int = 0                                          # Total turns this session
    interest_tags: list[str] = field(default_factory=list)      # Accumulated topic tags
    interest_score: float = 0.0                                  # 0.0 (low) to 1.0 (high)


class SessionManager:
    """Manages conversation sessions in Redis."""

    def __init__(self, redis: Redis) -> None:
        """Initialize with a Redis connection.

        Args:
            redis: Async Redis connection.
        """
        self._redis = redis
        self._ttl = timedelta(minutes=cfg.RAG_SESSION_TTL_MINUTES)
        self._max_history = cfg.RAG_SESSION_HISTORY_TURNS

    async def load(self, session_id: str, author_id: str) -> SessionContext:
        """Load or create a session context.

        Args:
            session_id: UUID of the chat session.
            author_id: UUID of the author (namespace).

        Returns:
            SessionContext with history and interest data.
        """
        key = self._key(author_id, session_id)
        data = await self._redis.hgetall(key)

        if not data:
            return SessionContext(session_id=session_id, author_id=author_id)

        history = json.loads(data.get("history", "[]"))
        interest_tags = json.loads(data.get("interest_tags", "[]"))

        return SessionContext(
            session_id=session_id,
            author_id=author_id,
            history=history,
            selected_book_id=data.get("selected_book_id"),
            is_cross_book=data.get("is_cross_book", "false") == "true",
            turn_count=int(data.get("turn_count", 0)),
            interest_tags=interest_tags,
            interest_score=float(data.get("interest_score", 0.0)),
        )

    async def save(
        self,
        context: SessionContext,
        user_message: str,
        assistant_message: str,
        new_tags: list[str] | None = None,
    ) -> None:
        """Persist updated session after a turn.

        Appends new messages to history, trims to max_history,
        extracts interest tags from the user message, and updates
        the interest profile using compute_interest_score.

        Args:
            context: Current session context.
            user_message: The user's message text.
            assistant_message: The bot's response text.
            new_tags: Optional pre-extracted topic tags (auto-extracted if None).
        """
        # Append new turn
        context.history.append({"role": "user", "content": user_message})
        context.history.append({"role": "assistant", "content": assistant_message})

        # Trim to max history (keep pairs: user+assistant)
        max_messages = self._max_history * 2
        if len(context.history) > max_messages:
            context.history = context.history[-max_messages:]

        # Auto-extract interest tags from the user message if not provided
        detected_tags = new_tags if new_tags is not None else extract_interest_tags(user_message)

        # Update interest profile
        context.turn_count += 1
        if detected_tags:
            context.interest_tags.extend(detected_tags)
            context.interest_tags = list(dict.fromkeys(context.interest_tags))[-20:]  # Keep last 20 unique

        # Recompute interest score using context module
        context.interest_score = compute_interest_score(context.turn_count, context.interest_tags)

        # Persist to Redis
        key = self._key(context.author_id, context.session_id)
        mapping = {
            "history": json.dumps(context.history),
            "selected_book_id": context.selected_book_id or "",
            "is_cross_book": "true" if context.is_cross_book else "false",
            "turn_count": str(context.turn_count),
            "interest_tags": json.dumps(context.interest_tags),
            "interest_score": str(context.interest_score),
        }
        await self._redis.hset(key, mapping=mapping)
        await self._redis.expire(key, self._ttl)
        logger.debug("Session saved", session_id=context.session_id, turns=context.turn_count)

    async def set_selected_book(
        self, session_id: str, author_id: str, book_id: str | None, is_cross: bool = False
    ) -> None:
        """Update the selected book for this session.

        Args:
            session_id: UUID of the session.
            author_id: UUID of the author.
            book_id: UUID of the selected book, or None for cross-book.
            is_cross: True if searching all books.
        """
        key = self._key(author_id, session_id)
        await self._redis.hset(key, mapping={
            "selected_book_id": book_id or "",
            "is_cross_book": "true" if is_cross else "false",
        })
        await self._redis.expire(key, self._ttl)

    async def delete(self, session_id: str, author_id: str) -> None:
        """Delete a session (on explicit logout or expiry cleanup).

        Args:
            session_id: UUID of the session.
            author_id: UUID of the author.
        """
        await self._redis.delete(self._key(author_id, session_id))

    def _key(self, author_id: str, session_id: str) -> str:
        """Build the Redis key for a session.

        Args:
            author_id: UUID of the author.
            session_id: UUID of the session.

        Returns:
            Redis key string.
        """
        return f"{_SESSION_PREFIX}{author_id}:{session_id}"