# backend/app/api/shopping.py
import uuid
from datetime import datetime, timezone, date as date_type
from decimal import Decimal
from fastapi import APIRouter, Depends, HTTPException, Query
from fastapi.responses import Response
from sqlalchemy import select, text, or_
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.core.database import get_session
from app.models.shopping import ShoppingList, ListItem, Product, Store
from app.schemas.shopping import (
    ShoppingListCreate, ShoppingListUpdate, ShoppingListResponse,
    ShoppingListDetailResponse, ListItemCreate, ListItemUpdate,
    ListItemResponse, ProductCreate, ProductUpdate, ProductResponse,
    StoreCreate, StoreUpdate, StoreResponse,
)

router = APIRouter()


def _iso_week_label() -> str:
    now = datetime.now(tz=timezone.utc)
    iso = now.isocalendar()
    return f"S{iso[1]} {iso[0]}"


def _item_to_response(item: ListItem) -> ListItemResponse:
    display_name = item.custom_name or (item.product.name if item.product else "Article inconnu")
    return ListItemResponse(
        id=item.id,
        product_id=item.product_id,
        custom_name=item.custom_name,
        display_name=display_name,
        quantity=item.quantity,
        unit=item.unit,
        is_checked=item.is_checked,
        price_recorded=item.price_recorded,
        carried_over=item.carried_over,
        sort_order=item.sort_order,
    )


def _list_to_response(lst: ShoppingList) -> ShoppingListResponse:
    items = lst.items if lst.items is not None else []
    return ShoppingListResponse(
        id=lst.id,
        name=lst.name,
        store_id=lst.store_id,
        week_date=lst.week_date,
        status=lst.status,
        created_at=lst.created_at,
        item_count=len(items),
        checked_count=sum(1 for i in items if i.is_checked),
    )


# ── Stores ────────────────────────────────────────────────────────────────────

@router.get("/stores", response_model=list[StoreResponse])
async def list_stores(session: AsyncSession = Depends(get_session)):
    result = await session.execute(select(Store).order_by(Store.name))
    return result.scalars().all()


@router.post("/stores", response_model=StoreResponse, status_code=201)
async def create_store(payload: StoreCreate, session: AsyncSession = Depends(get_session)):
    store = Store(**payload.model_dump())
    session.add(store)
    await session.commit()
    await session.refresh(store)
    return store


@router.patch("/stores/{store_id}", response_model=StoreResponse)
async def update_store(store_id: uuid.UUID, payload: StoreUpdate, session: AsyncSession = Depends(get_session)):
    store = await session.get(Store, store_id)
    if not store:
        raise HTTPException(404, "Boutique introuvable")
    for field, value in payload.model_dump(exclude_unset=True).items():
        setattr(store, field, value)
    await session.commit()
    await session.refresh(store)
    return store


@router.delete("/stores/{store_id}", status_code=204)
async def delete_store(store_id: uuid.UUID, session: AsyncSession = Depends(get_session)):
    store = await session.get(Store, store_id)
    if not store:
        raise HTTPException(404, "Boutique introuvable")
    await session.delete(store)
    await session.commit()
    return Response(status_code=204)


# ── Products ──────────────────────────────────────────────────────────────────

@router.get("/products", response_model=list[ProductResponse])
async def search_products(
    q: str | None = Query(default=None),
    limit: int = 500,
    session: AsyncSession = Depends(get_session),
):
    stmt = select(Product).order_by(Product.frequency_score.desc(), Product.name)
    if q:
        stmt = stmt.where(or_(Product.name.ilike(f"%{q}%"), Product.brand.ilike(f"%{q}%")))
    stmt = stmt.limit(limit)
    result = await session.execute(stmt)
    return result.scalars().all()


@router.post("/products", response_model=ProductResponse, status_code=201)
async def create_product(payload: ProductCreate, session: AsyncSession = Depends(get_session)):
    product = Product(**payload.model_dump())
    session.add(product)
    await session.commit()
    await session.refresh(product)
    return product


@router.patch("/products/{product_id}", response_model=ProductResponse)
async def update_product(
    product_id: uuid.UUID,
    payload: ProductUpdate,
    session: AsyncSession = Depends(get_session),
):
    product = await session.get(Product, product_id)
    if not product:
        raise HTTPException(404, "Produit introuvable")
    for field, value in payload.model_dump(exclude_unset=True).items():
        setattr(product, field, value)
    await session.commit()
    await session.refresh(product)
    return product


@router.delete("/products/{product_id}", status_code=204)
async def delete_product(product_id: uuid.UUID, session: AsyncSession = Depends(get_session)):
    product = await session.get(Product, product_id)
    if not product:
        raise HTTPException(404, "Produit introuvable")
    await session.delete(product)
    await session.commit()
    return Response(status_code=204)


# ── Lists ─────────────────────────────────────────────────────────────────────

@router.get("/lists", response_model=list[ShoppingListResponse])
async def list_shopping_lists(session: AsyncSession = Depends(get_session)):
    stmt = (
        select(ShoppingList)
        .options(selectinload(ShoppingList.items))
        .order_by(ShoppingList.created_at.desc())
    )
    result = await session.execute(stmt)
    lists = result.scalars().all()
    return [_list_to_response(lst) for lst in lists]


@router.post("/lists", response_model=ShoppingListDetailResponse, status_code=201)
async def create_shopping_list(
    payload: ShoppingListCreate,
    session: AsyncSession = Depends(get_session),
):
    data = payload.model_dump()
    if not data.get('name'):
        data['name'] = _iso_week_label()
    lst = ShoppingList(**data)
    session.add(lst)
    await session.commit()
    await session.refresh(lst, ["items"])
    return ShoppingListDetailResponse(
        **_list_to_response(lst).model_dump(),
        items=[],
    )


@router.get("/lists/{list_id}", response_model=ShoppingListDetailResponse)
async def get_shopping_list(list_id: uuid.UUID, session: AsyncSession = Depends(get_session)):
    stmt = (
        select(ShoppingList)
        .where(ShoppingList.id == list_id)
        .options(selectinload(ShoppingList.items).selectinload(ListItem.product))
    )
    result = await session.execute(stmt)
    lst = result.scalar_one_or_none()
    if not lst:
        raise HTTPException(404, "Liste introuvable")
    sorted_items = sorted(lst.items, key=lambda i: (i.sort_order or 999, str(i.id)))
    return ShoppingListDetailResponse(
        **_list_to_response(lst).model_dump(),
        items=[_item_to_response(i) for i in sorted_items],
    )


@router.patch("/lists/{list_id}", response_model=ShoppingListDetailResponse)
async def update_shopping_list(
    list_id: uuid.UUID,
    payload: ShoppingListUpdate,
    session: AsyncSession = Depends(get_session),
):
    stmt = (
        select(ShoppingList)
        .where(ShoppingList.id == list_id)
        .options(selectinload(ShoppingList.items).selectinload(ListItem.product))
    )
    result = await session.execute(stmt)
    lst = result.scalar_one_or_none()
    if not lst:
        raise HTTPException(404, "Liste introuvable")
    for field, value in payload.model_dump(exclude_unset=True).items():
        setattr(lst, field, value)
    await session.commit()
    sorted_items = sorted(lst.items, key=lambda i: (i.sort_order or 999, str(i.id)))
    return ShoppingListDetailResponse(
        **_list_to_response(lst).model_dump(),
        items=[_item_to_response(i) for i in sorted_items],
    )


@router.delete("/lists/{list_id}", status_code=204)
async def delete_shopping_list(list_id: uuid.UUID, session: AsyncSession = Depends(get_session)):
    lst = await session.get(ShoppingList, list_id)
    if not lst:
        raise HTTPException(404, "Liste introuvable")
    await session.delete(lst)
    await session.commit()
    return Response(status_code=204)


# ── Items ─────────────────────────────────────────────────────────────────────

@router.post("/lists/{list_id}/items", response_model=ListItemResponse, status_code=201)
async def add_item(
    list_id: uuid.UUID,
    payload: ListItemCreate,
    session: AsyncSession = Depends(get_session),
):
    lst = await session.get(ShoppingList, list_id)
    if not lst:
        raise HTTPException(404, "Liste introuvable")
    item = ListItem(list_id=list_id, **payload.model_dump())
    session.add(item)
    await session.commit()
    stmt = (
        select(ListItem)
        .where(ListItem.id == item.id)
        .options(selectinload(ListItem.product))
    )
    result = await session.execute(stmt)
    item = result.scalar_one()
    return _item_to_response(item)


@router.patch("/lists/{list_id}/items/{item_id}", response_model=ListItemResponse)
async def update_item(
    list_id: uuid.UUID,
    item_id: uuid.UUID,
    payload: ListItemUpdate,
    session: AsyncSession = Depends(get_session),
):
    stmt = (
        select(ListItem)
        .where(ListItem.id == item_id, ListItem.list_id == list_id)
        .options(selectinload(ListItem.product))
    )
    result = await session.execute(stmt)
    item = result.scalar_one_or_none()
    if not item:
        raise HTTPException(404, "Article introuvable")

    was_checked = item.is_checked
    for field, value in payload.model_dump(exclude_unset=True).items():
        setattr(item, field, value)

    # Mise à jour des stats produit lors du premier cochage
    if not was_checked and item.is_checked and item.product_id:
        product = await session.get(Product, item.product_id)
        if product:
            today = date_type.today()
            if product.last_purchased_at and product.last_purchased_at < today:
                days = (today - product.last_purchased_at).days
                if product.avg_interval_days is None:
                    product.avg_interval_days = Decimal(str(days))
                else:
                    # Moyenne mobile exponentielle (70 % passé, 30 % nouvel intervalle)
                    product.avg_interval_days = Decimal(str(
                        round(float(product.avg_interval_days) * 0.7 + days * 0.3, 1)
                    ))
            product.last_purchased_at = today
            product.frequency_score += 1

    await session.commit()
    await session.refresh(item, ["product"])
    return _item_to_response(item)


@router.delete("/lists/{list_id}/items/{item_id}", status_code=204)
async def delete_item(
    list_id: uuid.UUID,
    item_id: uuid.UUID,
    session: AsyncSession = Depends(get_session),
):
    stmt = select(ListItem).where(ListItem.id == item_id, ListItem.list_id == list_id)
    result = await session.execute(stmt)
    item = result.scalar_one_or_none()
    if not item:
        raise HTTPException(404, "Article introuvable")
    await session.delete(item)
    await session.commit()
    return Response(status_code=204)


@router.post("/lists/generate", response_model=ShoppingListDetailResponse, status_code=201)
async def generate_magic_list(session: AsyncSession = Depends(get_session)):
    """Génère une liste à partir du score de fréquence (retard / intervalle moyen)."""

    query = text("""
        WITH achats AS (
            SELECT
                COALESCE(li.custom_name, p.name) AS nom,
                li.product_id,
                li.custom_name,
                p.default_unit,
                sl.created_at::date AS date_achat
            FROM shopping.list_items li
            JOIN shopping.lists sl ON sl.id = li.list_id
            LEFT JOIN shopping.products p ON p.id = li.product_id
            WHERE li.is_checked = true
        ),
        achats_with_lag AS (
            SELECT
                nom,
                product_id,
                custom_name,
                default_unit,
                date_achat,
                date_achat - LAG(date_achat) OVER (PARTITION BY nom ORDER BY date_achat) AS interval_days
            FROM achats
        ),
        stats AS (
            SELECT
                nom,
                product_id,
                custom_name,
                default_unit,
                MAX(date_achat) AS last_purchased,
                COUNT(*) AS nb_achats,
                AVG(interval_days) AS avg_interval_days
            FROM achats_with_lag
            GROUP BY nom, product_id, custom_name, default_unit
        )
        SELECT
            nom,
            product_id,
            custom_name,
            default_unit,
            last_purchased,
            nb_achats,
            COALESCE(avg_interval_days, 30) AS avg_interval_days,
            (CURRENT_DATE - last_purchased)::float
                / NULLIF(COALESCE(avg_interval_days, 30), 0) AS score
        FROM stats
        WHERE (CURRENT_DATE - last_purchased)::float
              / NULLIF(COALESCE(avg_interval_days, 30), 0) >= 0.7
        ORDER BY score DESC
        LIMIT 50
    """)

    result = await session.execute(query)
    rows = result.mappings().all()

    new_list = ShoppingList(name=_iso_week_label(), status="draft")
    session.add(new_list)
    await session.flush()

    for row in rows:
        session.add(ListItem(
            list_id=new_list.id,
            product_id=row["product_id"],
            custom_name=row["custom_name"],
            unit=row["default_unit"],
        ))

    await session.commit()

    stmt = (
        select(ShoppingList)
        .where(ShoppingList.id == new_list.id)
        .options(selectinload(ShoppingList.items).selectinload(ListItem.product))
    )
    result2 = await session.execute(stmt)
    new_list = result2.scalar_one()
    sorted_items = sorted(new_list.items, key=lambda i: (i.sort_order or 999, str(i.id)))

    return ShoppingListDetailResponse(
        **_list_to_response(new_list).model_dump(),
        items=[_item_to_response(i) for i in sorted_items],
    )


@router.post("/lists/{list_id}/finish", response_model=ShoppingListDetailResponse)
async def finish_shopping(list_id: uuid.UUID, session: AsyncSession = Depends(get_session)):
    stmt = (
        select(ShoppingList)
        .where(ShoppingList.id == list_id)
        .options(selectinload(ShoppingList.items).selectinload(ListItem.product))
    )
    result = await session.execute(stmt)
    lst = result.scalar_one_or_none()
    if not lst:
        raise HTTPException(404, "Liste introuvable")

    lst.status = "done"

    unchecked = [i for i in lst.items if not i.is_checked]
    if unchecked:
        new_list = ShoppingList(store_id=lst.store_id, status="draft", name=_iso_week_label())
        session.add(new_list)
        await session.flush()
        for item in unchecked:
            session.add(ListItem(
                list_id=new_list.id,
                product_id=item.product_id,
                custom_name=item.custom_name,
                quantity=item.quantity,
                unit=item.unit,
                sort_order=item.sort_order,
                carried_over=True,
            ))

    await session.commit()
    sorted_items = sorted(lst.items, key=lambda i: (i.sort_order or 999, str(i.id)))
    return ShoppingListDetailResponse(
        **_list_to_response(lst).model_dump(),
        items=[_item_to_response(i) for i in sorted_items],
    )