import os
from dataclasses import dataclass
from pathlib import Path

# The modal shows this many days of run history; retention can never be shorter.
HISTORY_DAYS = 30

# Shared by the systemd service (EnvironmentFile=) and manage.py, so both always use the same DB.
DEFAULT_ENV_FILE = "/etc/backup-dashboard/backup-dashboard.env"


@dataclass(frozen=True)
class Settings:
    db_path: Path
    retention_days: int = 90
    # Dev only: serve ../public from the API so you can run without nginx.
    serve_static: bool = False
    # Microsoft 365 sign-in names allowed into the admin pages (lowercase)
    admins: frozenset[str] = frozenset()


def read_env_file(path: Path) -> dict[str, str]:
    """Parse simple KEY=VALUE lines (the subset systemd's EnvironmentFile accepts)."""
    values = {}
    try:
        lines = path.read_text().splitlines()
    except FileNotFoundError:
        return values
    for line in lines:
        line = line.strip()
        if not line or line.startswith("#") or "=" not in line:
            continue
        key, _, value = line.partition("=")
        values[key.strip()] = value.strip().strip("\"'")
    return values


def load_settings() -> Settings:
    # Real environment variables win over the env file; the env file wins over dev defaults.
    env = read_env_file(Path(os.environ.get("BACKUP_DASH_ENV_FILE", DEFAULT_ENV_FILE))) | os.environ
    return Settings(
        db_path=Path(env.get("BACKUP_DASH_DB", "backup-dashboard.db")),
        retention_days=max(HISTORY_DAYS, int(env.get("BACKUP_DASH_RETENTION_DAYS", "90"))),
        serve_static=env.get("BACKUP_DASH_SERVE_STATIC") == "1",
        admins=parse_admins(env.get("BACKUP_DASH_ADMINS", "")),
    )


def parse_admins(value: str) -> frozenset[str]:
    """'kyle@example.com, Pat@Example.com' -> {'kyle@example.com', 'pat@example.com'}"""
    return frozenset(part.strip().lower() for part in value.replace(";", ",").split(",") if part.strip())