"""Configuration for LangGraph checkpointer."""

from typing import Literal

from pydantic import BaseModel, Field

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


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

    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'.",
    )
    use_postgres: bool = Field(
        default=True,
        description=(
            "When type='postgres', set false to keep the Postgres DSN in config "
            "but run the checkpointer on SQLite instead."
        ),
    )
    sqlite_connection_string: str | None = Field(
        default=None,
        description=(
            "SQLite file used when type='postgres' and use_postgres=false. "
            "Defaults to the first dual_read_sqlite_paths entry or 'store.db'."
        ),
    )
    dual_read_enabled: bool = Field(
        default=False,
        description=(
            "When type='postgres', read from Postgres first and fall back to legacy "
            "SQLite checkpoint files when Postgres does not have the requested data."
        ),
    )
    dual_read_sqlite_paths: list[str] = Field(
        default_factory=list,
        description=(
            "Legacy SQLite checkpoint database paths used for read fallback. "
            "Plain paths are resolved the same way as SQLite connection_string."
        ),
    )


# Global configuration instance — None means no checkpointer is configured.
_checkpointer_config: CheckpointerConfig | None = None


def get_checkpointer_config() -> CheckpointerConfig | None:
    """Get the current checkpointer configuration, or None if not configured."""
    return _checkpointer_config


def set_checkpointer_config(config: CheckpointerConfig | None) -> None:
    """Set the checkpointer configuration."""
    global _checkpointer_config
    _checkpointer_config = config


def load_checkpointer_config_from_dict(config_dict: dict) -> None:
    """Load checkpointer configuration from a dictionary."""
    global _checkpointer_config
    _checkpointer_config = CheckpointerConfig(**config_dict)