from __future__ import annotations

from dataclasses import dataclass
from typing import Callable


@dataclass(frozen=True, slots=True)
class HeaderButton:
    """A prominent header link pointing to a local page or an external URL."""

    label: str
    page: str | int | float | Callable[..., object] | None = None
    href: str | None = None
    section: str | int | float | None = None
    new_tab: bool = False

    def __post_init__(self) -> None:
        label = str(self.label).strip()
        if not label:
            raise ValueError("Header button label cannot be empty")
        object.__setattr__(self, "label", label)
        if (self.page is None) == (self.href is None):
            raise ValueError("HeaderButton requires exactly one of page= or href=")
        if self.href is not None and not str(self.href).strip():
            raise ValueError("Header button href cannot be empty")

    @classmethod
    def local(
        cls,
        label: str,
        page: str | int | float | Callable[..., object],
        *,
        section: str | int | float | None = None,
    ) -> HeaderButton:
        return cls(label=label, page=page, section=section)

    @classmethod
    def external(cls, label: str, href: str, *, new_tab: bool = True) -> HeaderButton:
        return cls(label=label, href=href, new_tab=new_tab)


__all__ = ["HeaderButton"]