fn_registry/python/functions/infra/cache_to_sqlite.py

"""Cache key-value persistido en SQLite con TTL y lazy eviction."""

import json
import sqlite3
import threading
import time


class CacheStore:
    """Cache key-value respaldado en SQLite con soporte de TTL y namespaces."""

    _schema = """
    CREATE TABLE IF NOT EXISTS cache (
        namespace TEXT NOT NULL,
        key TEXT NOT NULL,
        value TEXT NOT NULL,
        created_at REAL NOT NULL,
        expires_at REAL,
        PRIMARY KEY (namespace, key)
    );
    """

    def __init__(self, db_path: str, namespace: str = "default") -> None:
        self._db_path = db_path
        self._namespace = namespace
        self._hits = 0
        self._misses = 0
        self._lock = threading.Lock()
        self._local = threading.local()
        self._init_db()

    def _conn(self) -> sqlite3.Connection:
        """Retorna una conexion SQLite thread-local."""
        if not hasattr(self._local, "conn"):
            conn = sqlite3.connect(self._db_path, check_same_thread=False)
            conn.execute("PRAGMA journal_mode=WAL")
            self._local.conn = conn
        return self._local.conn

    def _init_db(self) -> None:
        conn = self._conn()
        conn.execute(self._schema)
        conn.commit()

    def _evict_expired(self, conn: sqlite3.Connection) -> None:
        """Elimina entradas expiradas del namespace actual (lazy eviction)."""
        now = time.time()
        conn.execute(
            "DELETE FROM cache WHERE namespace = ? AND expires_at IS NOT NULL AND expires_at <= ?",
            (self._namespace, now),
        )

    def get(self, key: str) -> object:
        """Retorna el valor o None si no existe o esta expirado."""
        with self._lock:
            conn = self._conn()
            self._evict_expired(conn)
            conn.commit()
            row = conn.execute(
                "SELECT value FROM cache WHERE namespace = ? AND key = ?",
                (self._namespace, key),
            ).fetchone()
            if row is None:
                self._misses += 1
                return None
            self._hits += 1
            return json.loads(row[0])

    def set(self, key: str, value: object, ttl: float = 0) -> None:
        """Almacena un valor. ttl en segundos; 0 = sin expiracion."""
        now = time.time()
        expires_at = (now + ttl) if ttl > 0 else None
        with self._lock:
            conn = self._conn()
            conn.execute(
                """
                INSERT INTO cache (namespace, key, value, created_at, expires_at)
                VALUES (?, ?, ?, ?, ?)
                ON CONFLICT(namespace, key) DO UPDATE SET
                    value = excluded.value,
                    created_at = excluded.created_at,
                    expires_at = excluded.expires_at
                """,
                (self._namespace, key, json.dumps(value), now, expires_at),
            )
            conn.commit()

    def delete(self, key: str) -> bool:
        """Elimina una entrada. Retorna True si existia."""
        with self._lock:
            conn = self._conn()
            cursor = conn.execute(
                "DELETE FROM cache WHERE namespace = ? AND key = ?",
                (self._namespace, key),
            )
            conn.commit()
            return cursor.rowcount > 0

    def clear(self) -> int:
        """Elimina todas las entradas del namespace. Retorna filas eliminadas."""
        with self._lock:
            conn = self._conn()
            cursor = conn.execute(
                "DELETE FROM cache WHERE namespace = ?",
                (self._namespace,),
            )
            conn.commit()
            return cursor.rowcount

    def stats(self) -> dict:
        """Retorna estadisticas del store: hits, misses y size actual."""
        with self._lock:
            conn = self._conn()
            self._evict_expired(conn)
            conn.commit()
            row = conn.execute(
                "SELECT COUNT(*) FROM cache WHERE namespace = ?",
                (self._namespace,),
            ).fetchone()
            size = row[0] if row else 0
            return {"hits": self._hits, "misses": self._misses, "size": size}

    def get_or_set(self, key: str, factory: callable, ttl: float = 0) -> object:
        """Retorna el valor cacheado o llama factory() y lo almacena."""
        value = self.get(key)
        if value is None:
            value = factory()
            self.set(key, value, ttl)
        return value


def cache_to_sqlite(db_path: str, namespace: str = "default") -> CacheStore:
    """Crea un CacheStore respaldado en SQLite.

    Args:
        db_path: Ruta al archivo SQLite (se crea si no existe).
        namespace: Espacio de nombres logico dentro de la base de datos.

    Returns:
        CacheStore con metodos get/set/delete/clear/stats/get_or_set.
    """
    return CacheStore(db_path, namespace)