from __future__ import annotations

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

from models.calendars import Calendar
from shared.infrastructure.data_client import fetch_data
from shared.contracts.dtos import PostDTO, dto_from_dict
from shared.infrastructure.actions import call_action
import unicodedata
import re


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

from shared.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:
    raw = await fetch_data("blog", "post-by-slug", params={"slug": post_slug}, required=False)
    post = dto_from_dict(PostDTO, raw) if raw else None
    if not post:
        return False

    cal = (
        await sess.execute(
            select(Calendar).where(
                Calendar.container_type == "page",
                Calendar.container_id == post.id,
                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()
    await call_action("relations", "unrelate", payload={
        "relation_type": "page->calendar",
        "from_id": cal.container_id, "to_id": cal.id,
    })
    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)
    if slug in ("admin", "markets", "payments", "entries"):
        raise CalendarError(f'"{slug}" is a reserved name and cannot be used as a calendar name.')

    # Ensure post exists (avoid silent FK errors in some DBs)
    raw = await fetch_data("blog", "post-by-id", params={"id": post_id}, required=False)
    post = dto_from_dict(PostDTO, raw) if raw else 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.container_type == "page", Calendar.container_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()
            await call_action("relations", "relate", payload={
                "relation_type": "page->calendar",
                "from_id": post_id, "to_id": existing.id,
                "label": existing.name,
                "metadata": {"slug": existing.slug},
            })
            return existing
        raise CalendarError(f'Calendar with slug "{slug}" already exists for post {post_id}.')

    cal = Calendar(container_type="page", container_id=post_id, name=name, slug=slug)
    sess.add(cal)
    await sess.flush()
    await call_action("relations", "relate", payload={
        "relation_type": "page->calendar",
        "from_id": post_id, "to_id": cal.id,
        "label": cal.name,
        "metadata": {"slug": cal.slug},
    })
    return cal