"""Foods service layer — business logic + DB access (spec §8.1 rules 2–3, 7).

ORM objects never leave this module; functions return Pydantic schemas.
Handlers stay thin (~15 lines) by calling into these functions.
"""

from datetime import datetime, timezone

from sqlalchemy import select
from sqlalchemy.orm import Session

from models import Food
from schemas import FoodCreate, FoodRead, FoodUpdate


# ── Shared query helpers (§8.1 rule 7) ───────────────────────────────────────


def _not_deleted():
    """Shared filter: exclude soft-deleted foods. Use everywhere search/recent
    queries filter — never copy-paste per-endpoint."""
    return Food.deleted_at.is_(None)


def _base_search_stmt(db: Session, include_deleted: bool = False):
    """Base statement for food queries. Applies soft-delete filter unless
    include_deleted is True."""
    stmt = select(Food)
    if not include_deleted:
        stmt = stmt.where(_not_deleted())
    return stmt


# ── CRUD ─────────────────────────────────────────────────────────────────────


def list_foods(
    db: Session,
    q: str | None = None,
    barcode: str | None = None,
    limit: int = 50,
    offset: int = 0,
    include_deleted: bool = False,
) -> list[FoodRead]:
    """Search foods. Supports q (matches name AND brand), barcode (exact match),
    limit/offset pagination, and include_deleted toggle."""
    stmt = _base_search_stmt(db, include_deleted=include_deleted)

    if q:
        stmt = stmt.where(Food.name.contains(q) | Food.brand.contains(q))
    if barcode:
        stmt = stmt.where(Food.barcode == barcode)

    stmt = stmt.limit(limit).offset(offset)
    foods = db.scalars(stmt).all()
    return [FoodRead.model_validate(f) for f in foods]


def get_food(db: Session, food_id: int) -> FoodRead | None:
    """Get a single food by id. INCLUDES soft-deleted foods (historical log
    rendering depends on this — spec §2.1). Returns None for unknown id."""
    food = db.get(Food, food_id)
    if food is None:
        return None
    return FoodRead.model_validate(food)


def create_food(db: Session, data: FoodCreate) -> FoodRead:
    """Create a food. Checks barcode uniqueness on live foods (409).
    SQLite treats NULL barcodes as distinct, so multiple barcode-less foods
    are fine."""
    if data.barcode is not None:
        existing = db.scalar(
            select(Food).where(Food.barcode == data.barcode)
        )
        if existing is not None:
            raise BarcodeConflictError(data.barcode)

    now = datetime.now(timezone.utc).replace(tzinfo=None)
    food = Food(
        name=data.name,
        brand=data.brand,
        barcode=data.barcode,
        source=data.source,
        is_meal=data.is_meal,
        unit_type=data.unit_type,
        calories_per_unit=data.calories_per_unit,
        protein_per_unit=data.protein_per_unit,
        carbs_per_unit=data.carbs_per_unit,
        fat_per_unit=data.fat_per_unit,
        fiber_per_unit=data.fiber_per_unit,
        saturated_fat_per_unit=data.saturated_fat_per_unit,
        sugars_per_unit=data.sugars_per_unit,
        sodium_per_unit=data.sodium_per_unit,
        serving_size_g=data.serving_size_g,
        serving_name=data.serving_name,
        off_data=data.off_data,
        created_at=now,
        updated_at=now,
    )
    db.add(food)
    db.commit()
    db.refresh(food)
    return FoodRead.model_validate(food)


def update_food(db: Session, food_id: int, data: FoodUpdate) -> FoodRead | None:
    """Update editable fields on a food. Only supplied (non-None) fields are
    changed. Returns None if food not found."""
    food = db.get(Food, food_id)
    if food is None:
        return None

    update_data = data.model_dump(exclude_unset=True)

    # Check barcode uniqueness if barcode is being changed to a non-None value
    if "barcode" in update_data and update_data["barcode"] is not None:
        new_bc = update_data["barcode"]
        existing = db.scalar(
            select(Food).where(Food.barcode == new_bc, Food.id != food_id)
        )
        if existing is not None:
            raise BarcodeConflictError(new_bc)

    for field, value in update_data.items():
        setattr(food, field, value)

    food.updated_at = datetime.now(timezone.utc).replace(tzinfo=None)
    db.commit()
    db.refresh(food)
    return FoodRead.model_validate(food)


def delete_food(db: Session, food_id: int) -> FoodRead | None:
    """Soft-delete a food: sets deleted_at timestamp. Returns None if not found."""
    food = db.get(Food, food_id)
    if food is None:
        return None

    food.deleted_at = datetime.now(timezone.utc).replace(tzinfo=None)
    food.updated_at = datetime.now(timezone.utc).replace(tzinfo=None)
    db.commit()
    db.refresh(food)
    return FoodRead.model_validate(food)


# ── Errors ───────────────────────────────────────────────────────────────────


class BarcodeConflictError(Exception):
    """Raised when a barcode already exists on another food."""
    def __init__(self, barcode: str):
        super().__init__(f"Barcode '{barcode}' already exists")
        self.barcode = barcode