"""Configuration for LangGraph checkpointer."""

from typing import Literal

from pydantic import BaseModel, Field

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

SqliteMode = Literal["full", "shallow"]
"""Persistence mode for the SQLite checkpointer.

- ``full`` — retain all checkpoint history (default, backward-compatible).
- ``shallow`` — keep only the latest checkpoint per thread, deleting old
  records before each write to prevent unbounded database growth.
"""


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'.",
    )
    sqlite_mode: SqliteMode = Field(
        default="full",
        description="SQLite persistence mode. "
        "'full' retains all checkpoint history (default). "
        "'shallow' keeps only the latest checkpoint per thread, "
        "deleting old records before each write.",
    )


# 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)