"""Daily log service layer — business logic + DB access (spec §8.1 rules 2–3).

- Log entries reference foods; embedded food data is included in responses.
- sort_order for new entries defaults to end of day: max(sort_order) + 1
  for that date, starting at 1 if no entries exist yet.
- Soft-deleted foods are rejected on create (404 — you can't log what you
  can't search), but still render in historical GET responses (§2.1).

ORM objects never leave this module; functions return Pydantic schemas.
"""

from datetime import date, datetime, timezone

from sqlalchemy import func, select
from sqlalchemy.orm import Session, joinedload

from models import DailyLogEntry, Food
from schemas import (
    DaySummaryNutrition,
    DaySummaryResponse,
    LogEntryCreate,
    LogEntryRead,
    LogEntryUpdate,
)
from services import nutrition
from services import targets as targets_svc


def _now() -> datetime:
    return datetime.now(timezone.utc).replace(tzinfo=None)


def _load_entry_with_food(db: Session, entry_id: int) -> DailyLogEntry | None:
    """Eager-load a single entry with its food relationship."""
    return db.scalar(
        select(DailyLogEntry)
        .where(DailyLogEntry.id == entry_id)
        .options(joinedload(DailyLogEntry.food))
    )


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


def get_log_entries(db: Session, lookup_date: date) -> list[LogEntryRead]:
    """All entries for a date, ordered by sort_order then id, with embedded
    food data eagerly loaded. Soft-deleted foods still render (§2.1)."""
    stmt = (
        select(DailyLogEntry)
        .where(DailyLogEntry.date == lookup_date)
        .options(joinedload(DailyLogEntry.food))
        .order_by(DailyLogEntry.sort_order, DailyLogEntry.id)
    )
    entries = db.scalars(stmt).all()
    return [LogEntryRead.model_validate(e) for e in entries]


def create_log_entry(db: Session, data: LogEntryCreate) -> LogEntryRead:
    """Create a log entry.

    Validates that food_id exists and is not soft-deleted.
    sort_order defaults to end of day for the given date.

    Raises FoodNotAvailableError if food_id is unknown or the food is
    soft-deleted (you can't log what you can't search — spec §2.1).
    """
    food = db.get(Food, data.food_id)
    if food is None or food.deleted_at is not None:
        raise FoodNotAvailableError(data.food_id)

    max_sort = db.scalar(
        select(func.max(DailyLogEntry.sort_order)).where(
            DailyLogEntry.date == data.date
        )
    )
    sort_order = (max_sort or 0) + 1

    entry = DailyLogEntry(
        date=data.date,
        food_id=data.food_id,
        quantity=data.quantity,
        meal_slot=data.meal_slot,
        sort_order=sort_order,
        created_at=_now(),
    )
    db.add(entry)
    db.commit()

    # Re-query with eager-loaded food for the response
    return LogEntryRead.model_validate(_load_entry_with_food(db, entry.id))


def update_log_entry(
    db: Session, entry_id: int, data: LogEntryUpdate
) -> LogEntryRead | None:
    """Update quantity, meal_slot, and/or sort_order.

    Uses model_dump(exclude_unset=True) so only explicitly-provided fields
    are changed. Send {"meal_slot": null} to clear the slot.

    Returns None if the entry is not found.
    """
    entry = db.get(DailyLogEntry, entry_id)
    if entry is None:
        return None

    update_data = data.model_dump(exclude_unset=True)
    for field, value in update_data.items():
        setattr(entry, field, value)

    db.commit()
    return LogEntryRead.model_validate(_load_entry_with_food(db, entry_id))


def delete_log_entry(db: Session, entry_id: int) -> bool:
    """Hard-delete a log entry (§2.3 has no soft-delete).

    Returns True if deleted, False if not found.
    """
    entry = db.get(DailyLogEntry, entry_id)
    if entry is None:
        return False
    db.delete(entry)
    db.commit()
    return True


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


class FoodNotAvailableError(Exception):
    """Raised when a food_id is unknown or the food is soft-deleted."""
    def __init__(self, food_id: int):
        super().__init__(f"Food {food_id} not available for logging")
        self.food_id = food_id


# ── Day Summary (TICKET-004) ─────────────────────────────────────────────────


def get_day_summary(db: Session, lookup_date: date) -> DaySummaryResponse:
    """Compute nutrition totals for a date vs. the applicable target.

    1. Loads all log entries for the date with food data eagerly joined.
    2. For each entry, scales the food's per-unit nutrition to the logged
       quantity via nutrition.entry_nutrition() — weight-type foods get
       (qty/100)× scaling, count-type foods get qty× scaling (§2.1).
    3. Meal entries (is_meal=True) currently contribute 0 because their
       per_unit fields are null per the CHECK constraint.
       TODO: TICKET-007 — replace with recursive component summation.
    4. Looks up the target covering the date via the half-open interval
       lookup from targets.get_target_for_date(). Returns null if none.

    Returns a DaySummaryResponse with summed totals and the applicable
    target (or null).
    """
    entries = db.scalars(
        select(DailyLogEntry)
        .where(DailyLogEntry.date == lookup_date)
        .options(joinedload(DailyLogEntry.food))
    ).all()

    # Sum nutrition across all entries for the date.
    # TODO: TICKET-007 — meal entries currently contribute 0 because their
    # per_unit fields are null per the CHECK constraint. Real meal nutrition
    # will be derived by recursively summing component foods' nutrition.
    # When that lands, replace the flat entry_nutrition() call with a
    # meal-aware sum function from services/nutrition.py.
    totals = {field: 0.0 for field in nutrition.NUTRITION_FIELDS}
    for entry in entries:
        entry_nut = nutrition.entry_nutrition(entry.food, entry.quantity)
        for field, value in entry_nut.items():
            totals[field] += value

    target = targets_svc.get_target_for_date(db, lookup_date)

    return DaySummaryResponse(
        date=lookup_date,
        totals=DaySummaryNutrition(**totals),
        target=target,
    )