# backend/ai_history.py
"""Persistent assistant conversation history (#95).

Each authenticated user owns a flat list of conversation sessions tagged with
their context (mode / vault / directory / documents). Sessions survive page
reloads and are the source of truth for the panel history menu (#96 sidebar
"Historique IA" reads the same store).

Format of a session (JS/JSON shape kept identical to the client, minus
transient fields):

    {
      "id": "s-…",
      "title": "…",
      "mode": "directory" | "documents" | "general",
      "vault": "…" | None,
      "directory": "…" | "",
      "documents": [{"vault": "…", "path": "…"}],
      "context": "directory-…",        # _contextKey() of the assistant
      "createdAt": 1234567890,
      "updatedAt": 1234567890,
      "messages": [{"role": "user|assistant", "content": "…"}]
    }

Sessions are capped per user (see MAX_SESSIONS); the oldest ones are dropped
when the cap is reached.
"""

import json
import logging
import shutil
from pathlib import Path
from typing import Any

logger = logging.getLogger("obsigate.ai_history")

AI_HISTORY_DIR = Path("data/ai_history")
MAX_SESSIONS = 200


def _get_user_file(username: str) -> Path:
    AI_HISTORY_DIR.mkdir(parents=True, exist_ok=True)
    return AI_HISTORY_DIR / f"{username}.json"


def _read_sessions(username: str) -> list[dict[str, Any]]:
    path = _get_user_file(username)
    if not path.exists():
        return []
    try:
        data = json.loads(path.read_text(encoding="utf-8"))
    except Exception as e:  # pragma: no cover - defensive I/O guard
        logger.error(f"Failed to read AI history for {username}: {e}")
        return []
    if not isinstance(data, list):
        return []
    return [s for s in data if isinstance(s, dict)]


def _write_sessions(username: str, sessions: list[dict[str, Any]]) -> None:
    path = _get_user_file(username)
    try:
        tmp = path.with_suffix(".tmp")
        tmp.write_text(
            json.dumps(sessions, indent=2, ensure_ascii=False),
            encoding="utf-8",
        )
        shutil.move(str(tmp), str(path))
    except Exception as e:  # pragma: no cover - defensive I/O guard
        logger.error(f"Failed to write AI history for {username}: {e}")


def _summary(session: dict[str, Any]) -> dict[str, Any]:
    """Compact representation (no messages) used by the list endpoint."""
    messages = session.get("messages") or []
    preview = ""
    for msg in reversed(messages):
        content = (msg.get("content") or "").strip() if isinstance(msg, dict) else ""
        if content:
            preview = content[:120]
            break
    return {
        "id": session.get("id", ""),
        "title": session.get("title", "") or "",
        "mode": session.get("mode", "general"),
        "vault": session.get("vault"),
        "directory": session.get("directory", ""),
        "context": session.get("context", ""),
        "createdAt": session.get("createdAt", 0),
        "updatedAt": session.get("updatedAt", session.get("createdAt", 0)),
        "message_count": len(messages),
        "preview": preview,
    }


def list_sessions(username: str, *, include_messages: bool = False) -> list[dict[str, Any]]:
    """Return the user's sessions, most recently updated first.

    With ``include_messages=False`` (default) a compact summary is returned;
    the full conversation is fetched per id via :func:`get_session`.
    """
    if not username:
        return []
    sessions = sorted(
        _read_sessions(username),
        key=lambda s: s.get("updatedAt") or s.get("createdAt") or 0,
        reverse=True,
    )
    if include_messages:
        return sessions
    return [_summary(s) for s in sessions]


def get_session(username: str, session_id: str) -> dict[str, Any] | None:
    if not username or not session_id:
        return None
    for session in _read_sessions(username):
        if session.get("id") == session_id:
            return session
    return None


def upsert_session(username: str, session: dict[str, Any]) -> dict[str, Any] | None:
    """Create or update a conversation for the user.

    Returns the stored session, or None when there is no valid id.
    """
    if not username:
        return None
    session_id = (session.get("id") or "").strip()
    if not session_id:
        return None

    now = session.get("updatedAt") or session.get("createdAt") or 0
    stored = {
        "id": session_id,
        "title": session.get("title", "") or "",
        "mode": session.get("mode") or "general",
        "vault": session.get("vault"),
        "directory": session.get("directory", ""),
        "documents": session.get("documents") or [],
        "context": session.get("context", ""),
        "createdAt": session.get("createdAt") or now,
        "updatedAt": now,
        "messages": session.get("messages") or [],
    }

    sessions = _read_sessions(username)
    replaced = False
    for i, existing in enumerate(sessions):
        if existing.get("id") == session_id:
            sessions[i] = stored
            replaced = True
            break
    if not replaced:
        sessions.append(stored)

    sessions.sort(key=lambda s: s.get("updatedAt") or s.get("createdAt") or 0, reverse=True)
    if len(sessions) > MAX_SESSIONS:
        logger.info(f"AI history cap reached for {username}: trimming to {MAX_SESSIONS}")
        sessions = sessions[:MAX_SESSIONS]

    _write_sessions(username, sessions)
    return stored


def delete_session(username: str, session_id: str) -> bool:
    if not username or not session_id:
        return False
    sessions = _read_sessions(username)
    remaining = [s for s in sessions if s.get("id") != session_id]
    if len(remaining) == len(sessions):
        return False
    _write_sessions(username, remaining)
    return True