"""Slug value object for URL-friendly identifiers."""

import re
from dataclasses import dataclass

from app.domain.value_objects.base import ValueObject


@dataclass(frozen=True, slots=True)
class Slug(ValueObject[str]):
    """URL slug value object."""

    MAX_LENGTH: int = 200
    SLUG_PATTERN: str = r"^[a-z0-9]+(?:-[a-z0-9]+)*$"

    def _validate(self) -> None:
        if not isinstance(self.value, str):
            raise ValueError("Slug must be a string")
        if len(self.value) > self.MAX_LENGTH:
            raise ValueError(f"Slug must be at most {self.MAX_LENGTH} characters")
        if not re.match(self.SLUG_PATTERN, self.value):
            raise ValueError(
                "Slug must contain only lowercase letters, numbers, and hyphens"
            )

    @classmethod
    def from_title(cls, title: str) -> "Slug":
        """Generate slug from title."""
        # Convert to lowercase, replace spaces with hyphens
        slug = title.lower().strip()
        # Keep only alphanumeric, spaces, and hyphens
        slug = re.sub(r"[^a-z0-9\s-]", "", slug)
        # Replace spaces and multiple hyphens with single hyphen
        slug = re.sub(r"[-\s]+", "-", slug)
        # Limit length and strip hyphens
        max_len = 200  # Same as MAX_LENGTH
        slug = slug[:max_len].strip("-")
        # Ensure we have at least one character
        if not slug:
            slug = "post"
        return cls(value=slug)