from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, Field
from sqlalchemy import func
from sqlalchemy.exc import IntegrityError
from sqlalchemy.orm import Session

from app.core.auth_dependency import require_session
from app.core.slugify import unique_slugify
from app.db import get_db
from app.models.category import Category
from app.models.channel_category import channel_categories

router = APIRouter(dependencies=[Depends(require_session)])


class CategoryCreate(BaseModel):
    name: str = Field(min_length=1, max_length=255)


class CategoryUpdate(BaseModel):
    name: str = Field(min_length=1, max_length=255)


class CategoryReorder(BaseModel):
    category_ids: list[int]


def _existing_slugs(db: Session, exclude_id: int | None = None) -> set[str]:
    query = db.query(Category.slug)
    if exclude_id is not None:
        query = query.filter(Category.id != exclude_id)
    return {row[0] for row in query.all()}


def _name_taken(db: Session, name: str, exclude_id: int | None = None) -> bool:
    query = db.query(Category.name)
    if exclude_id is not None:
        query = query.filter(Category.id != exclude_id)
    target = name.casefold()
    return any(row[0].casefold() == target for row in query.all())


def _serialize(db: Session, category: Category, counts: dict[int, int]) -> dict:
    return {
        "id": category.id,
        "name": category.name,
        "slug": category.slug,
        "sort_order": category.sort_order,
        "channel_count": counts.get(category.id, 0),
    }


@router.get("/categories")
def list_categories(db: Session = Depends(get_db)) -> list[dict]:
    categories = db.query(Category).order_by(Category.sort_order.asc(), Category.id.asc()).all()
    count_rows = (
        db.query(channel_categories.c.category_id, func.count(channel_categories.c.channel_id))
        .group_by(channel_categories.c.category_id)
        .all()
    )
    counts = dict(count_rows)
    return [_serialize(db, c, counts) for c in categories]


@router.post("/categories", status_code=201)
def create_category(payload: CategoryCreate, db: Session = Depends(get_db)) -> dict:
    name = payload.name.strip()
    if not name:
        raise HTTPException(status_code=400, detail="Category name must not be empty")

    if _name_taken(db, name):
        raise HTTPException(status_code=409, detail="Category with this name already exists")

    slug = unique_slugify(name, _existing_slugs(db))
    max_sort_order = db.query(func.max(Category.sort_order)).scalar() or 0

    category = Category(name=name, slug=slug, sort_order=max_sort_order + 1)
    db.add(category)
    try:
        db.commit()
    except IntegrityError:
        db.rollback()
        raise HTTPException(status_code=409, detail="Category with this name already exists")

    return _serialize(db, category, {})


@router.patch("/categories/{category_id}")
def update_category(category_id: int, payload: CategoryUpdate, db: Session = Depends(get_db)) -> dict:
    category = db.get(Category, category_id)
    if category is None:
        raise HTTPException(status_code=404, detail="Category not found")

    name = payload.name.strip()
    if not name:
        raise HTTPException(status_code=400, detail="Category name must not be empty")

    if _name_taken(db, name, exclude_id=category_id):
        raise HTTPException(status_code=409, detail="Category with this name already exists")

    category.name = name
    category.slug = unique_slugify(name, _existing_slugs(db, exclude_id=category_id))
    try:
        db.commit()
    except IntegrityError:
        db.rollback()
        raise HTTPException(status_code=409, detail="Category with this name already exists")

    return _serialize(db, category, {})


@router.delete("/categories/{category_id}", status_code=204)
def delete_category(category_id: int, db: Session = Depends(get_db)) -> None:
    category = db.get(Category, category_id)
    if category is None:
        raise HTTPException(status_code=404, detail="Category not found")
    db.delete(category)
    db.commit()


@router.post("/categories/reorder")
def reorder_categories(payload: CategoryReorder, db: Session = Depends(get_db)) -> list[dict]:
    categories = {c.id: c for c in db.query(Category).all()}

    if set(payload.category_ids) != set(categories.keys()):
        raise HTTPException(status_code=400, detail="category_ids must contain exactly all existing category ids")

    for index, category_id in enumerate(payload.category_ids):
        categories[category_id].sort_order = index

    db.commit()

    ordered = db.query(Category).order_by(Category.sort_order.asc(), Category.id.asc()).all()
    return [_serialize(db, c, {}) for c in ordered]