"""Configuration for LangGraph checkpointer."""

from typing import Literal

from pydantic import BaseModel, ConfigDict, Field

CheckpointerType = Literal["memory", "sqlite", "postgres"]


class CheckpointerConfig(BaseModel):
    """Configuration for LangGraph state persistence checkpointer."""

    model_config = ConfigDict(frozen=True)

    type: CheckpointerType = Field(
        description="Checkpointer backend type. "
        "'memory' is in-process only (lost on restart). "
        "'sqlite' persists to a local file (requires langgraph-checkpoint-sqlite). "
        "'postgres' persists to PostgreSQL (requires langgraph-checkpoint-postgres)."
    )
    connection_string: str | None = Field(
        default=None,
        description="Connection string for sqlite (file path) or postgres (DSN). "
        "Required for sqlite and postgres types. "
        "For sqlite, use a file path like '.deer-flow/checkpoints.db' or ':memory:' for in-memory. "
        "For postgres, use a DSN like 'postgresql://user:pass@localhost:5432/db'.",
    )