from abc import ABCMeta
from pathlib import Path
from typing import Optional


CURRENT_DIR = Path(__file__).parent


def _extract_style(maybe_style: Optional[str], name: str) -> str:
    if maybe_style is not None:
        maybe_path = Path(maybe_style)
        if maybe_path.exists():
            return maybe_path.read_text(encoding="UTF-8")
        return maybe_style
    maybe_path = CURRENT_DIR / "styles" / f"{name}.css"
    if maybe_path.exists():
        return maybe_path.read_text(encoding="UTF-8")
    return ""


class CSS(ABCMeta):
    """Cascade stylesheets, i.e. combine all ancestor styles"""

    def __new__(cls, name, bases, attrs):
        Page = super().__new__(cls, name, bases, attrs)
        # Use a locally defined STYLE or the one from styles directory
        Page.STYLE = _extract_style(attrs.get("STYLE_FILE"), name)
        Page.STYLE += attrs.get("STYLE_APPEND", "")
        # Combine with all ancestor styles
        Page.CSS = "".join(
            Class.STYLE
            for Class in reversed(Page.__mro__)
            if type(Class) is CSS
        )
        return Page