Initial working translator implementation

backend/sessions.py

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+"""In-memory translation session store with 24h TTL."""
+
+import uuid
+from datetime import datetime, timezone, timedelta
+from typing import Any
+
+from backend.models import TranslationSession
+
+
+class SessionStore:
+    """Thread-safe-ish in-memory dict for translation sessions.
+
+    Each session is keyed by a UUID and has a 24-hour TTL.
+    Expired sessions are lazily cleaned on access.
+    """
+
+    def __init__(self, ttl_hours: int = 24):
+        self._store: dict[str, dict[str, Any]] = {}
+        self.ttl_hours = ttl_hours
+
+    def create(self, session_data: TranslationSession) -> str:
+        session_id = uuid.uuid4().hex[:16]
+        self._store[session_id] = {
+            "data": session_data.model_dump(),
+            "created_at": datetime.now(timezone.utc),
+            "updated_at": datetime.now(timezone.utc),
+        }
+        return session_id
+
+    def get(self, session_id: str) -> TranslationSession | None:
+        entry = self._store.get(session_id)
+        if entry is None:
+            return None
+        # Check TTL
+        now = datetime.now(timezone.utc)
+        age = now - entry["updated_at"]
+        if age > timedelta(hours=self.ttl_hours):
+            del self._store[session_id]
+            return None
+        # Touch (refresh TTL)
+        entry["updated_at"] = now
+        return TranslationSession(**entry["data"])
+
+    def update(self, session_id: str, data: dict[str, Any]) -> TranslationSession | None:
+        entry = self._store.get(session_id)
+        if entry is None:
+            return None
+        entry["data"].update(data)
+        entry["updated_at"] = datetime.now(timezone.utc)
+        return TranslationSession(**entry["data"])
+
+    def delete(self, session_id: str) -> bool:
+        if session_id in self._store:
+            del self._store[session_id]
+            return True
+        return False
+
+    def cleanup_expired(self):
+        """Remove all expired sessions."""
+        now = datetime.now(timezone.utc)
+        expired_keys = [
+            k for k, v in self._store.items()
+            if (now - v["updated_at"]) > timedelta(hours=self.ttl_hours)
+        ]
+        for k in expired_keys:
+            del self._store[k]
+
+
+# Singleton instance
+session_store = SessionStore(ttl_hours=24)