"""Configuration for beads MCP server."""

import os
import sys
from pathlib import Path

from pydantic import field_validator
from pydantic_settings import BaseSettings, SettingsConfigDict


def _default_beads_path() -> str:
    """Get default bd executable path.

    Returns:
        Default path to bd executable (~/.local/bin/bd)
    """
    return str(Path.home() / ".local" / "bin" / "bd")


class Config(BaseSettings):
    """Server configuration loaded from environment variables."""

    model_config = SettingsConfigDict(env_prefix="")

    beads_path: str = _default_beads_path()
    beads_db: str | None = None
    beads_actor: str | None = None
    beads_no_auto_flush: bool = False
    beads_no_auto_import: bool = False

    @field_validator("beads_path")
    @classmethod
    def validate_beads_path(cls, v: str) -> str:
        """Validate BEADS_PATH points to an executable bd binary.

        Args:
            v: Path to bd executable

        Returns:
            Validated path

        Raises:
            ValueError: If path is invalid or not executable
        """
        path = Path(v)

        if not path.exists():
            raise ValueError(
                f"bd executable not found at: {v}\n"
                + "Please verify BEADS_PATH points to a valid bd executable."
            )

        if not os.access(v, os.X_OK):
            raise ValueError(
                f"bd executable at {v} is not executable.\nPlease check file permissions."
            )

        return v

    @field_validator("beads_db")
    @classmethod
    def validate_beads_db(cls, v: str | None) -> str | None:
        """Validate BEADS_DB points to an existing database file.

        Args:
            v: Path to database file or None

        Returns:
            Validated path or None

        Raises:
            ValueError: If path is set but file doesn't exist
        """
        if v is None:
            return v

        path = Path(v)
        if not path.exists():
            raise ValueError(
                f"BEADS_DB points to non-existent file: {v}\n"
                + "Please verify the database path is correct."
            )

        return v


def load_config() -> Config:
    """Load and validate configuration from environment variables.

    Returns:
        Validated configuration

    Raises:
        SystemExit: If configuration is invalid
    """
    try:
        return Config()
    except Exception as e:
        default_path = _default_beads_path()
        print(
            f"Configuration Error: {e}\n\n"
            + "Environment variables:\n"
            + f"  BEADS_PATH            - Path to bd executable (default: {default_path})\n"
            + "  BEADS_DB              - Optional path to beads database file\n"
            + "  BEADS_ACTOR           - Actor name for audit trail (default: $USER)\n"
            + "  BEADS_NO_AUTO_FLUSH   - Disable automatic JSONL sync (default: false)\n"
            + "  BEADS_NO_AUTO_IMPORT  - Disable automatic JSONL import (default: false)\n\n"
            + "Make sure bd is installed and the path is correct.",
            file=sys.stderr,
        )
        sys.exit(1)