"""
backend/api/session_manager.py — Session Manager (Fase 1 ADR-S26-S30)

Responsabilità: gestione del ciclo di vita delle sessioni utente.
Disaccoppia la logica di sessione dal Brain/Executor.

Livelli di storage (tiered):
  Tier 1 — In-memory LRU     (hot sessions, max 256, sub-ms)
  Tier 2 — Redis TTL         (sessioni attive cross-restart, TTL 24h)
  Tier 3 — Supabase          (storico permanente, resume dopo shutdown)

Cycle di vita di una sessione:
  CREATED → ACTIVE → [PAUSED] → ENDED | EXPIRED

Invarianti ADR:
  S26: ogni sessione è persistente (Tier 3)
  S27: ogni sessione ha correlation_id per tracciabilità
  S29: ogni componente sostituibile via feature flag (SESS_BACKEND=redis|supabase|memory)

Endpoints:
  POST   /api/sessions                    — crea sessione (auth: MACHINE)
  GET    /api/sessions/{session_id}       — recupera sessione (auth: MACHINE)
  PATCH  /api/sessions/{session_id}       — aggiorna metadata/status (auth: MACHINE)
  DELETE /api/sessions/{session_id}/end   — termina sessione (auth: MACHINE)
  GET    /api/sessions/status             — diagnostica (auth: MACHINE)
"""
import asyncio, json, time, uuid, logging, os
from collections import OrderedDict
from typing import Any
from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, Field
from .auth_guard import require_role, AuthRole
from .state import _sb

_logger = logging.getLogger("api.session_manager")

router = APIRouter(
    prefix="/api/sessions",
    tags=["session-manager"],
    dependencies=[Depends(require_role(AuthRole.MACHINE))],
)

_SESS_TTL_S  = int(os.getenv("SESSION_TTL_SECONDS", str(24 * 3600)))  # 24h default
_LRU_MAX     = int(os.getenv("SESSION_LRU_MAX",     "256"))
_SESS_TABLE  = "sessions"
_REDIS_PREFIX = "sess:"

# ── SessionStatus ──────────────────────────────────────────────────────────────
class SessionStatus:
    CREATED = "created"
    ACTIVE  = "active"
    PAUSED  = "paused"
    ENDED   = "ended"
    EXPIRED = "expired"


# ── In-memory LRU (Tier 1) ─────────────────────────────────────────────────────
_lru: "OrderedDict[str, dict]" = OrderedDict()
_lru_lock = asyncio.Lock()

async def _lru_get(session_id: str) -> dict | None:
    async with _lru_lock:
        if session_id in _lru:
            _lru.move_to_end(session_id)
            return _lru[session_id]
    return None

async def _lru_set(session_id: str, session: dict) -> None:
    async with _lru_lock:
        _lru[session_id] = session
        _lru.move_to_end(session_id)
        while len(_lru) > _LRU_MAX:
            _lru.popitem(last=False)


# ── Redis helpers (Tier 2) ─────────────────────────────────────────────────────

async def _redis_get_session(session_id: str) -> dict | None:
    try:
        import httpx
        redis_url   = os.getenv("UPSTASH_REDIS_REST_URL",   "")
        redis_token = os.getenv("UPSTASH_REDIS_REST_TOKEN", "")
        if not redis_url: return None
        async with httpx.AsyncClient(timeout=2.0) as c:
            r = await c.post(redis_url, json=["GET", _REDIS_PREFIX + session_id],
                             headers={"Authorization": f"Bearer {redis_token}"})
            data = r.json()
            if data.get("result"):
                return json.loads(data["result"])
    except Exception as exc:
        _logger.debug("[session_mgr] redis get skip: %s", exc)
    return None

async def _redis_set_session(session_id: str, session: dict) -> None:
    try:
        import httpx
        redis_url   = os.getenv("UPSTASH_REDIS_REST_URL",   "")
        redis_token = os.getenv("UPSTASH_REDIS_REST_TOKEN", "")
        if not redis_url: return
        async with httpx.AsyncClient(timeout=2.0) as c:
            await c.post(redis_url,
                         json=["SET", _REDIS_PREFIX + session_id, json.dumps(session), "EX", _SESS_TTL_S],
                         headers={"Authorization": f"Bearer {redis_token}"})
    except Exception as exc:
        _logger.debug("[session_mgr] redis set skip: %s", exc)

async def _redis_del_session(session_id: str) -> None:
    try:
        import httpx
        redis_url   = os.getenv("UPSTASH_REDIS_REST_URL",   "")
        redis_token = os.getenv("UPSTASH_REDIS_REST_TOKEN", "")
        if not redis_url: return
        async with httpx.AsyncClient(timeout=2.0) as c:
            await c.post(redis_url,
                         json=["DEL", _REDIS_PREFIX + session_id],
                         headers={"Authorization": f"Bearer {redis_token}"})
    except Exception as exc:
        _logger.debug("[session_mgr] redis del skip: %s", exc)


# ── Supabase helpers (Tier 3) ──────────────────────────────────────────────────

async def _supa_upsert(session: dict) -> None:
    if not _sb: return
    try:
        _sb.table(_SESS_TABLE).upsert({
            "id":             session["session_id"],
            "status":         session["status"],
            "user_id":        session.get("user_id"),
            "correlation_id": session.get("correlation_id"),
            "metadata":       session.get("metadata", {}),
            "created_at":     session.get("created_at"),
            "last_active_at": session.get("last_active_at"),
            "ended_at":       session.get("ended_at"),
        }).execute()
    except Exception as exc:
        _logger.debug("[session_mgr] supabase upsert skip: %s", exc)

async def _supa_get(session_id: str) -> dict | None:
    if not _sb: return None
    try:
        res = _sb.table(_SESS_TABLE).select("*").eq("id", session_id).limit(1).execute()
        if res.data:
            r = res.data[0]
            return {
                "session_id":     r["id"],
                "status":         r.get("status", SessionStatus.ACTIVE),
                "user_id":        r.get("user_id"),
                "correlation_id": r.get("correlation_id"),
                "metadata":       r.get("metadata", {}),
                "created_at":     r.get("created_at"),
                "last_active_at": r.get("last_active_at"),
                "ended_at":       r.get("ended_at"),
            }
    except Exception as exc:
        _logger.debug("[session_mgr] supabase get skip: %s", exc)
    return None


# ── Core session operations ─────────────────────────────────────────────────────

async def create_session(user_id: str | None = None, metadata: dict | None = None) -> dict:
    """Crea una nuova sessione e la persiste su tutti i tier. Chiamabile internamente."""
    now = time.time()
    session = {
        "session_id":     str(uuid.uuid4()),
        "status":         SessionStatus.CREATED,
        "user_id":        user_id,
        "correlation_id": str(uuid.uuid4()),
        "metadata":       metadata or {},
        "created_at":     now,
        "last_active_at": now,
        "ended_at":       None,
    }
    await _lru_set(session["session_id"], session)
    asyncio.create_task(_redis_set_session(session["session_id"], session))
    asyncio.create_task(_supa_upsert(session))
    _logger.info("[session_mgr] created session=%s user=%s", session["session_id"][:8], user_id)
    return session

async def get_session(session_id: str) -> dict | None:
    """Recupera una sessione, cercando nei tier in ordine di velocità."""
    s = await _lru_get(session_id)
    if s: return s
    s = await _redis_get_session(session_id)
    if s:
        await _lru_set(session_id, s)
        return s
    s = await _supa_get(session_id)
    if s:
        await _lru_set(session_id, s)
        asyncio.create_task(_redis_set_session(session_id, s))
    return s

async def touch_session(session_id: str) -> None:
    """Aggiorna last_active_at e rinnova il TTL Redis."""
    s = await get_session(session_id)
    if not s: return
    s["last_active_at"] = time.time()
    s["status"] = SessionStatus.ACTIVE
    await _lru_set(session_id, s)
    asyncio.create_task(_redis_set_session(session_id, s))
    asyncio.create_task(_supa_upsert(s))


# ── Pydantic models ────────────────────────────────────────────────────────────

class CreateSessionRequest(BaseModel):
    user_id:  str | None  = None
    metadata: dict        = Field(default_factory=dict)

class PatchSessionRequest(BaseModel):
    status:   str | None  = None
    metadata: dict | None = None


# ── Endpoints ──────────────────────────────────────────────────────────────────

@router.post("", summary="Crea una nuova sessione")
async def create_session_endpoint(req: CreateSessionRequest):
    session = await create_session(user_id=req.user_id, metadata=req.metadata)
    return session

@router.get("/status", summary="Diagnostica Session Manager")
async def session_manager_status():
    async with _lru_lock:
        lru_count = len(_lru)
    return {
        "status":     "ok",
        "component":  "session_manager",
        "lru_sessions": lru_count,
        "lru_max":    _LRU_MAX,
        "session_ttl_s": _SESS_TTL_S,
        "tiers": {
            "memory": "active",
            "redis":  "active" if os.getenv("UPSTASH_REDIS_REST_URL") else "not_configured",
            "supabase": "active" if _sb else "not_configured",
        },
    }

@router.get("/{session_id}", summary="Recupera sessione")
async def get_session_endpoint(session_id: str):
    s = await get_session(session_id)
    if not s:
        raise HTTPException(404, detail=f"Sessione {session_id} non trovata")
    return s

@router.patch("/{session_id}", summary="Aggiorna sessione")
async def patch_session_endpoint(session_id: str, req: PatchSessionRequest):
    s = await get_session(session_id)
    if not s:
        raise HTTPException(404, detail=f"Sessione {session_id} non trovata")
    if req.status:
        s["status"] = req.status
    if req.metadata is not None:
        s["metadata"].update(req.metadata)
    s["last_active_at"] = time.time()
    await _lru_set(session_id, s)
    asyncio.create_task(_redis_set_session(session_id, s))
    asyncio.create_task(_supa_upsert(s))
    return s

@router.delete("/{session_id}/end", summary="Termina sessione")
async def end_session_endpoint(session_id: str):
    s = await get_session(session_id)
    if not s:
        raise HTTPException(404, detail=f"Sessione {session_id} non trovata")
    s["status"]   = SessionStatus.ENDED
    s["ended_at"] = time.time()
    await _lru_set(session_id, s)
    asyncio.create_task(_redis_del_session(session_id))
    asyncio.create_task(_supa_upsert(s))
    _logger.info("[session_mgr] ended session=%s", session_id[:8])
    return {"session_id": session_id, "status": SessionStatus.ENDED}