from __future__ import annotations

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from models.calendars import Calendar
from models.ghost_content import Post  # for FK existence checks
import unicodedata
import re


class CalendarError(ValueError):
    """Base error for calendar service operations."""

from suma_browser.app.utils import (
    utcnow
)

def slugify(value: str, max_len: int = 255) -> str:
    """
    Make a URL-friendly slug:
    - lowercase
    - remove accents
    - replace any non [a-z0-9]+ with '-'
    - no forward slashes
    - collapse multiple dashes
    - trim leading/trailing dashes
    """
    if value is None:
        value = ""
    # normalize accents -> ASCII
    value = unicodedata.normalize("NFKD", value)
    value = value.encode("ascii", "ignore").decode("ascii")
    value = value.lower()

    # explicitly block forward slashes
    value = value.replace("/", "-")

    # replace non-alnum with hyphen
    value = re.sub(r"[^a-z0-9]+", "-", value)
    # collapse multiple hyphens
    value = re.sub(r"-{2,}", "-", value)
    # trim hyphens and enforce length
    value = value.strip("-")[:max_len].strip("-")

    # fallback if empty
    return value or "calendar"


async def soft_delete(sess: AsyncSession, post_slug: str, calendar_slug: str) -> bool:
    cal = (
        await sess.execute(
            select(Calendar)
            .join(Post, Calendar.post_id == Post.id)
            .where(
                Post.slug == post_slug,
                Calendar.slug == calendar_slug,
                Calendar.deleted_at.is_(None),
            )
        )
    ).scalar_one_or_none()

    if not cal:
        return False

    cal.deleted_at = utcnow()
    await sess.flush()
    return True

async def create_calendar(sess: AsyncSession, post_id: int, name: str) -> Calendar:
    """
    Create a calendar for a post. Name must be unique per post.
    If a calendar with the same (post_id, name) exists but is soft-deleted,
    it will be revived (deleted_at=None).
    """
    name = (name or "").strip()
    if not name:
        raise CalendarError("Calendar name must not be empty.")
    slug=slugify(name)

    # Ensure post exists (avoid silent FK errors in some DBs)
    post = (await sess.execute(select(Post).where(Post.id == post_id))).scalar_one_or_none()
    if not post:
        raise CalendarError(f"Post {post_id} does not exist.")

    # Enforce: calendars can only be created on pages with the calendar feature
    if not post.is_page:
        raise CalendarError("Calendars can only be created on pages, not posts.")

    # Look for existing (including soft-deleted)
    q = await sess.execute(
        select(Calendar).where(Calendar.post_id == post_id, Calendar.name == name)
    )
    existing = q.scalar_one_or_none()

    if existing:
        if existing.deleted_at is not None:
            existing.deleted_at = None  # revive
            await sess.flush()
            return existing
        raise CalendarError(f'Calendar with slug "{slug}" already exists for post {post_id}.')

    cal = Calendar(post_id=post_id, name=name, slug=slug)
    sess.add(cal)
    await sess.flush()
    return cal