import os
import re
from pathlib import Path


_ENV_NAME = re.compile(r"^[A-Za-z_][A-Za-z0-9_]*$")


def load_env_file(path: Path) -> bool:
    """Load a simple dotenv file without overriding the process environment."""
    path = Path(path)
    if not path.is_file():
        return False
    for raw_line in path.read_text(encoding="utf-8-sig").splitlines():
        line = raw_line.strip()
        if not line or line.startswith("#"):
            continue
        if line.startswith("export "):
            line = line[7:].lstrip()
        key, separator, value = line.partition("=")
        key = key.strip()
        if not separator or not _ENV_NAME.fullmatch(key):
            continue
        value = value.strip()
        if len(value) >= 2 and value[0] == value[-1] and value[0] in {'"', "'"}:
            value = value[1:-1]
        os.environ.setdefault(key, value)
    return True


def load_project_environment(base_dir: Path) -> Path | None:
    """Select local/production dotenv while preserving injected server secrets."""
    base_dir = Path(base_dir)
    explicit = os.environ.get("DJANGO_ENV_FILE", "").strip()
    if explicit:
        selected = Path(explicit)
        if not selected.is_absolute():
            selected = base_dir / selected
    else:
        settings_module = os.environ.get("DJANGO_SETTINGS_MODULE", "")
        selected = base_dir / (".env.local" if settings_module.endswith(".dev") else ".env")
    load_env_file(selected)
    return selected if selected.is_file() else None