"""Helper functions for interacting with spool database objects."""

import json
import logging
from collections.abc import Sequence
from dataclasses import dataclass
from datetime import datetime, timezone

import sqlalchemy
from sqlalchemy import ColumnElement, case, func
from sqlalchemy.exc import NoResultFound
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import contains_eager, joinedload
from sqlalchemy.sql.functions import coalesce

from spoolman.api.v1.models import EventType, Spool, SpoolEvent
from spoolman.database import filament, models
from spoolman.database.extra_field_query import (
    ExtraFieldJoin,
    apply_extra_field_filters_and_sort,
    apply_spool_related_extra_filters,
    extra_field_join,
    extra_field_value_text,
)
from spoolman.database.utils import (
    SortOrder,
    add_where_clause_int,
    add_where_clause_int_opt,
    add_where_clause_str,
    add_where_clause_str_opt,
    parse_nested_field,
)
from spoolman.exceptions import ItemCreateError, ItemNotFoundError, SpoolMeasureError
from spoolman.extra_field_registry import EntityType, ExtraField, ExtraFieldType, get_extra_fields
from spoolman.math import weight_from_length
from spoolman.ws import websocket_manager

logger = logging.getLogger(__name__)


def utc_timezone_naive(dt: datetime) -> datetime:
    """Convert a datetime object to UTC and remove timezone info."""
    return dt.astimezone(tz=timezone.utc).replace(tzinfo=None)


async def create(
    *,
    db: AsyncSession,
    filament_id: int,
    remaining_weight: float | None = None,
    initial_weight: float | None = None,
    spool_weight: float | None = None,
    used_weight: float | None = None,
    first_used: datetime | None = None,
    last_used: datetime | None = None,
    price: float | None = None,
    location: str | None = None,
    lot_nr: str | None = None,
    comment: str | None = None,
    archived: bool = False,
    extra: dict[str, str | None] | None = None,
) -> models.Spool:
    """Add a new spool to the database. Leave weight empty to assume full spool."""
    filament_item = await filament.get_by_id(db, filament_id)

    # Set spool_weight to spool_weight if spool_weight is not null and spool_weight not provided
    if spool_weight is None and filament_item.spool_weight is not None:
        spool_weight = filament_item.spool_weight

    # Calculate initial_weight if not provided
    if initial_weight is None and filament_item.weight is not None:
        initial_weight = filament_item.weight

    if used_weight is None:
        if remaining_weight is not None:
            if initial_weight is None or initial_weight == 0:
                raise ItemCreateError(
                    "remaining_weight can only be used if the initial_weight is "
                    "defined or the filament has a weight set.",
                )
            used_weight = max(initial_weight - remaining_weight, 0)
        else:
            used_weight = 0

    # Convert datetime values to UTC and remove timezone info
    if first_used is not None:
        first_used = utc_timezone_naive(first_used)
    if last_used is not None:
        last_used = utc_timezone_naive(last_used)

    spool = models.Spool(
        filament=filament_item,
        registered=datetime.utcnow().replace(microsecond=0),
        initial_weight=initial_weight,
        spool_weight=spool_weight,
        used_weight=used_weight,
        price=price,
        first_used=first_used,
        last_used=last_used,
        location=location,
        lot_nr=lot_nr,
        comment=comment,
        archived=archived,
        extra=[models.SpoolField(key=k, value=v) for k, v in (extra or {}).items() if v is not None],
    )
    db.add(spool)
    await db.commit()
    await spool_changed(spool, EventType.ADDED)
    return spool


async def get_by_id(db: AsyncSession, spool_id: int) -> models.Spool:
    """Get a spool object from the database by the unique ID."""
    spool = await db.get(
        models.Spool,
        spool_id,
        options=[joinedload("*")],  # Load all nested objects as well
    )
    if spool is None:
        raise ItemNotFoundError(f"No spool with ID {spool_id} found.")
    return spool


async def find(  # noqa: C901, PLR0912
    *,
    db: AsyncSession,
    filament_name: str | None = None,
    filament_id: int | Sequence[int] | None = None,
    filament_material: str | None = None,
    filament_multi_color_direction: str | None = None,
    vendor_name: str | None = None,
    vendor_id: int | Sequence[int] | None = None,
    location: str | None = None,
    lot_nr: str | None = None,
    allow_archived: bool = False,
    extra_field_filters: dict[str, str] | None = None,
    filament_extra_field_filters: dict[str, str] | None = None,
    vendor_extra_field_filters: dict[str, str] | None = None,
    sort_by: dict[str, SortOrder] | None = None,
    limit: int | None = None,
    offset: int = 0,
) -> tuple[list[models.Spool], int]:
    """Find a list of spool objects by search criteria.

    Sort by a field by passing a dict with the field name as key and the sort order as value.
    The field name can contain nested fields, e.g. filament.name.

    Returns a tuple containing the list of items and the total count of matching items.
    """
    stmt = _apply_spool_filters(
        sqlalchemy.select(models.Spool),
        filament_name=filament_name,
        filament_id=filament_id,
        filament_material=filament_material,
        filament_multi_color_direction=filament_multi_color_direction,
        vendor_name=vendor_name,
        vendor_id=vendor_id,
        location=location,
        lot_nr=lot_nr,
        allow_archived=allow_archived,
    ).options(contains_eager(models.Spool.filament).contains_eager(models.Filament.vendor))

    total_count = None

    stmt = await apply_extra_field_filters_and_sort(
        db=db,
        stmt=stmt,
        base_obj=models.Spool,
        entity_type=EntityType.spool,
        extra_field_filters=extra_field_filters,
        sort_by=sort_by,
    )
    stmt = await apply_spool_related_extra_filters(
        db=db,
        stmt=stmt,
        filament_filters=filament_extra_field_filters,
        vendor_filters=vendor_extra_field_filters,
    )

    if sort_by is not None:
        for fieldstr, order in sort_by.items():
            # Check if this is a custom field sort
            if fieldstr.startswith("extra."):
                continue

            sorts = []
            if fieldstr == "remaining_weight":
                sorts.append(
                    coalesce(models.Spool.initial_weight, models.Filament.weight) - models.Spool.used_weight,
                )
            elif fieldstr == "remaining_length":
                # Simplified weight -> length formula. Absolute value is not correct but the proportionality
                # is still kept, which means the sort order is correct.
                sorts.append(
                    (coalesce(models.Spool.initial_weight, models.Filament.weight) - models.Spool.used_weight)
                    / models.Filament.density
                    / (models.Filament.diameter * models.Filament.diameter),
                )
            elif fieldstr == "used_length":
                sorts.append(
                    models.Spool.used_weight
                    / models.Filament.density
                    / (models.Filament.diameter * models.Filament.diameter),
                )
            elif fieldstr == "filament.combined_name":
                sorts.append(models.Vendor.name)
                sorts.append(models.Filament.name)
            elif fieldstr == "price":
                sorts.append(coalesce(models.Spool.price, models.Filament.price))
            else:
                sorts.append(parse_nested_field(models.Spool, fieldstr))

            if order == SortOrder.ASC:
                stmt = stmt.order_by(*(f.asc() for f in sorts))
            elif order == SortOrder.DESC:
                stmt = stmt.order_by(*(f.desc() for f in sorts))

    if limit is not None:
        total_count_stmt = stmt.with_only_columns(func.count(), maintain_column_froms=True).order_by(None)
        total_count = (await db.execute(total_count_stmt)).scalar()
        stmt = stmt.offset(offset).limit(limit)

    rows = await db.execute(
        stmt,
        execution_options={"populate_existing": True},
    )
    result = list(rows.unique().scalars().all())
    if total_count is None:
        total_count = len(result)

    return result, total_count


GROUP_BY_COLUMNS = {
    "filament": models.Spool.filament_id,
    "vendor": models.Filament.vendor_id,
    "material": models.Filament.material,
    "location": models.Spool.location,
}

# Prefix marking a reference to one of the spool's extra fields rather than a built-in column.
EXTRA_FIELD_PREFIX = "extra."

# Mirrors the Spool.location column width, so an over-long rename is a 400 and not a 500.
LOCATION_MAX_LENGTH = 64

# Extra fields whose value is a single plain string, and which can therefore be grouped on and
# renamed by value. Multi-choice is excluded because its value is a JSON *array*: two spools
# with overlapping-but-unequal selections are neither the same value nor cleanly different
# ones, and there is no single value to match or write.
SINGLE_VALUE_EXTRA_FIELD_TYPES = (ExtraFieldType.text, ExtraFieldType.choice)


def _apply_spool_filters(
    stmt: sqlalchemy.Select,
    *,
    filament_name: str | None = None,
    filament_id: int | Sequence[int] | None = None,
    filament_material: str | None = None,
    filament_multi_color_direction: str | None = None,
    vendor_name: str | None = None,
    vendor_id: int | Sequence[int] | None = None,
    location: str | None = None,
    lot_nr: str | None = None,
    allow_archived: bool = False,
) -> sqlalchemy.Select:
    """Apply the standard spool joins and where-clauses shared by find and find_groups."""
    stmt = stmt.join(models.Spool.filament, isouter=True).join(models.Filament.vendor, isouter=True)
    stmt = add_where_clause_int(stmt, models.Spool.filament_id, filament_id)
    stmt = add_where_clause_int_opt(stmt, models.Filament.vendor_id, vendor_id)
    stmt = add_where_clause_str(stmt, models.Vendor.name, vendor_name)
    stmt = add_where_clause_str_opt(stmt, models.Filament.name, filament_name)
    stmt = add_where_clause_str_opt(stmt, models.Filament.material, filament_material)
    stmt = add_where_clause_str_opt(stmt, models.Filament.multi_color_direction, filament_multi_color_direction)
    stmt = add_where_clause_str_opt(stmt, models.Spool.location, location)
    stmt = add_where_clause_str_opt(stmt, models.Spool.lot_nr, lot_nr)
    if not allow_archived:
        # archived is nullable with a default of false, so match both false and null.
        stmt = stmt.where(
            sqlalchemy.or_(
                models.Spool.archived.is_(False),
                models.Spool.archived.is_(None),
            ),
        )
    return stmt


async def _resolve_group_by(
    db: AsyncSession,
    group_by: str,
) -> tuple[ColumnElement, ColumnElement, ExtraFieldJoin | None]:
    """Resolve a group_by into the column to group on, the column to title groups by, and any join.

    Grouping is either on a built-in column or on one of the spool's extra fields. The latter
    lives in its own table, so it comes with a join the caller has to apply once the SELECT exists.
    """
    if group_by.startswith(EXTRA_FIELD_PREFIX):
        field_key = _extra_field_key(await get_extra_fields(db, EntityType.spool), group_by)
        join = extra_field_join(EntityType.spool, field_key)
        # The value is the group's title as well; there is no separate entity to name it.
        return join.value, join.value, join
    if group_by in GROUP_BY_COLUMNS:
        title_col = {
            "filament": models.Filament.name,
            "vendor": models.Vendor.name,
            "material": models.Filament.material,
            "location": models.Spool.location,
        }[group_by]
        return GROUP_BY_COLUMNS[group_by], title_col, None
    raise ValueError(
        f"Invalid group_by field '{group_by}'. Must be one of {sorted(GROUP_BY_COLUMNS)} "
        f"or '{EXTRA_FIELD_PREFIX}<spool extra field key>'.",
    )


def _extra_field_key(spool_fields: Sequence[ExtraField], reference: str) -> str:
    """Resolve an `extra.<key>` reference to its bare key, rejecting fields that can't carry one.

    Shared by grouping and by renaming a value, which need the same guarantee: the field exists,
    and one spool has exactly one plain string in it.
    """
    field_key = reference[len(EXTRA_FIELD_PREFIX) :]
    field = next((f for f in spool_fields if f.key == field_key), None)
    if field is None:
        raise ValueError(f"Unknown spool extra field '{field_key}'.")
    is_multi_choice = field.field_type == ExtraFieldType.choice and field.multi_choice
    if field.field_type not in SINGLE_VALUE_EXTRA_FIELD_TYPES or is_multi_choice:
        raise ValueError(
            f"Spool extra field '{field_key}' does not hold a single plain value. "
            f"Only text and single-choice fields do.",
        )
    return field_key


@dataclass
class SpoolGroupResult:
    """One aggregated spool group, with the grouped entity hydrated for its header."""

    key: object
    spool_count: int
    in_use_count: int
    total_remaining_weight: float
    last_used: datetime | None
    filament: models.Filament | None
    vendor: models.Vendor | None


async def find_groups(
    *,
    db: AsyncSession,
    group_by: str,
    filament_name: str | None = None,
    filament_id: int | Sequence[int] | None = None,
    filament_material: str | None = None,
    filament_multi_color_direction: str | None = None,
    vendor_name: str | None = None,
    vendor_id: int | Sequence[int] | None = None,
    location: str | None = None,
    lot_nr: str | None = None,
    allow_archived: bool = False,
    extra_field_filters: dict[str, str] | None = None,
    filament_extra_field_filters: dict[str, str] | None = None,
    vendor_extra_field_filters: dict[str, str] | None = None,
    sort_by: dict[str, SortOrder] | None = None,
    limit: int | None = None,
    offset: int = 0,
) -> tuple[list[SpoolGroupResult], int]:
    """Group matching spools by one axis and return per-group aggregates.

    Aggregation, group ordering and pagination happen in the database. Pagination is over
    groups, so a group is never split across pages and its aggregates are always complete.

    Returns a tuple of the requested page of groups and the total number of matching groups.
    """
    group_col, title_col, extra_join = await _resolve_group_by(db, group_by)

    # Remaining weight is computed (see Spool.from_db); mirror that formula so the sum is correct.
    # The fallback literal is 0.0 (float, not int): the weights are floats, and CockroachDB rejects
    # a COALESCE that mixes a float expression with an int literal ("incompatible COALESCE expressions").
    remaining_expr = coalesce(
        coalesce(models.Spool.initial_weight, models.Filament.weight) - models.Spool.used_weight,
        0.0,
    )
    # ...including its max(..., 0) clamp, so an over-used spool contributes 0 rather than a
    # negative number and the group total still matches the sum of the per-spool values.
    # CASE, not func.greatest: greatest() is not portable across all four supported databases.
    remaining_expr = case((remaining_expr < 0, 0.0), else_=remaining_expr)
    spool_count = func.count().label("spool_count")
    in_use_count = func.sum(case((models.Spool.used_weight > 0, 1), else_=0)).label("in_use_count")
    total_remaining = func.sum(remaining_expr).label("total_remaining_weight")
    last_used = func.max(models.Spool.last_used).label("last_used")

    stmt = sqlalchemy.select(
        group_col.label("group_key"),
        spool_count,
        in_use_count,
        total_remaining,
        last_used,
    )
    stmt = _apply_spool_filters(
        stmt,
        filament_name=filament_name,
        filament_id=filament_id,
        filament_material=filament_material,
        filament_multi_color_direction=filament_multi_color_direction,
        vendor_name=vendor_name,
        vendor_id=vendor_id,
        location=location,
        lot_nr=lot_nr,
        allow_archived=allow_archived,
    )
    if extra_join is not None:
        stmt = extra_join.apply(stmt, models.Spool.id)
    stmt = await apply_extra_field_filters_and_sort(
        db=db,
        stmt=stmt,
        base_obj=models.Spool,
        entity_type=EntityType.spool,
        extra_field_filters=extra_field_filters,
        sort_by=None,
    )
    stmt = await apply_spool_related_extra_filters(
        db=db,
        stmt=stmt,
        filament_filters=filament_extra_field_filters,
        vendor_filters=vendor_extra_field_filters,
    )
    stmt = stmt.group_by(group_col)

    # Total number of matching groups (before pagination).
    count_stmt = sqlalchemy.select(func.count()).select_from(stmt.order_by(None).subquery())
    total_count = (await db.execute(count_stmt)).scalar_one()

    # Group ordering. Every option is an aggregate (or the grouped column), so no non-grouped
    # bare column is referenced — portable across SQLite, PostgreSQL, MySQL and CockroachDB.
    order_exprs = {
        "group.spool_count": spool_count,
        "group.in_use_count": in_use_count,
        "group.total_remaining": total_remaining,
        "group.last_used": last_used,
        "group.title": func.min(title_col),
    }
    applied_sort = False
    if sort_by:
        for fieldstr, order in sort_by.items():
            expr = order_exprs.get(fieldstr)
            if expr is None:
                continue
            stmt = stmt.order_by(expr.asc() if order == SortOrder.ASC else expr.desc())
            applied_sort = True
    if not applied_sort:
        stmt = stmt.order_by(func.min(title_col).asc())

    if limit is not None:
        stmt = stmt.offset(offset).limit(limit)

    rows = (await db.execute(stmt)).all()

    # Hydrate the grouped entity for the header (filament/vendor). The value-keyed axes —
    # material, location, extra fields — are their own header and need nothing.
    keys = [row.group_key for row in rows if row.group_key is not None]
    filament_map: dict[int, models.Filament] = {}
    vendor_map: dict[int, models.Vendor] = {}
    if group_by == "filament" and keys:
        fstmt = (
            sqlalchemy.select(models.Filament)
            .where(models.Filament.id.in_(keys))
            .options(joinedload(models.Filament.vendor))
        )
        filament_map = {f.id: f for f in (await db.execute(fstmt)).unique().scalars().all()}
    elif group_by == "vendor" and keys:
        vstmt = sqlalchemy.select(models.Vendor).where(models.Vendor.id.in_(keys))
        vendor_map = {v.id: v for v in (await db.execute(vstmt)).unique().scalars().all()}

    return [
        SpoolGroupResult(
            key=row.group_key,
            spool_count=int(row.spool_count or 0),
            in_use_count=int(row.in_use_count or 0),
            total_remaining_weight=float(row.total_remaining_weight or 0),
            last_used=row.last_used,
            filament=filament_map.get(row.group_key) if group_by == "filament" else None,
            vendor=vendor_map.get(row.group_key) if group_by == "vendor" else None,
        )
        for row in rows
    ], total_count


async def update(
    *,
    db: AsyncSession,
    spool_id: int,
    data: dict,
) -> models.Spool:
    """Update the fields of a spool object."""
    spool = await get_by_id(db, spool_id)
    for k, v in data.items():
        if k == "filament_id":
            spool.filament = await filament.get_by_id(db, v)
            # If there is no initial_weight, calculate it from the filament weight
            if spool.initial_weight is None and spool.filament.weight is not None:
                spool.initial_weight = spool.filament.weight

        elif k == "remaining_weight":
            if spool.initial_weight is None:
                raise ItemCreateError("remaining_weight can only be used if initial_weight is set.")
            spool.used_weight = max(spool.initial_weight - v, 0)
        elif isinstance(v, datetime):
            setattr(spool, k, utc_timezone_naive(v))
        elif k == "extra":
            # Merged per key, the same as a filament's and a vendor's: only the keys present
            # in the patch are touched, and a null value means the spool has no value for
            # that field, so its row is dropped and not re-added — that is how a value that
            # has been set gets cleared.
            spool.extra = [f for f in spool.extra if f.key not in v]
            spool.extra.extend([models.SpoolField(key=k, value=v) for k, v in v.items() if v is not None])
        else:
            setattr(spool, k, v)
    await db.commit()
    await spool_changed(spool, EventType.UPDATED)
    return spool


async def delete(db: AsyncSession, spool_id: int) -> None:
    """Delete a spool object."""
    spool = await get_by_id(db, spool_id)
    await db.delete(spool)
    # Commit before notifying so the deletion is durable and visible to subsequent
    # requests; post-commit notification must be the last, infallible step.
    await db.commit()
    await spool_changed(spool, EventType.DELETED)


async def clear_extra_field(db: AsyncSession, key: str) -> None:
    """Delete all extra fields with a specific key."""
    await db.execute(
        sqlalchemy.delete(models.SpoolField).where(models.SpoolField.key == key),
    )
    await db.commit()


async def use_weight_safe(db: AsyncSession, spool_id: int, weight: float) -> None:
    """Consume filament from a spool by weight in a way that is safe against race conditions.

    Args:
        db (AsyncSession): Database session
        spool_id (int): Spool ID
        weight (float): Filament weight to consume, in grams

    """
    await db.execute(
        sqlalchemy.update(models.Spool)
        .where(models.Spool.id == spool_id)
        .values(
            used_weight=case(
                (models.Spool.used_weight + weight >= 0.0, models.Spool.used_weight + weight),
                else_=0.0,  # Set used_weight to 0 if the result would be negative
            ),
        ),
    )


async def use_weight(db: AsyncSession, spool_id: int, weight: float) -> models.Spool:
    """Consume filament from a spool by weight.

    Increases the used_weight attribute of the spool.
    Updates the first_used and last_used attributes where appropriate.

    Args:
        db (AsyncSession): Database session
        spool_id (int): Spool ID
        weight (float): Filament weight to consume, in grams

    Returns:
        models.Spool: Updated spool object

    """
    await use_weight_safe(db, spool_id, weight)

    spool = await get_by_id(db, spool_id)

    if spool.first_used is None:
        spool.first_used = datetime.utcnow().replace(microsecond=0)
    spool.last_used = datetime.utcnow().replace(microsecond=0)

    await db.commit()
    await spool_changed(spool, EventType.UPDATED)
    return spool


async def use_length(db: AsyncSession, spool_id: int, length: float) -> models.Spool:
    """Consume filament from a spool by length.

    Increases the used_weight attribute of the spool.
    Updates the first_used and last_used attributes where appropriate.

    Args:
        db (AsyncSession): Database session
        spool_id (int): Spool ID
        length (float): Length of filament to consume, in mm

    Returns:
        models.Spool: Updated spool object

    """
    # Get filament diameter and density
    result = await db.execute(
        sqlalchemy.select(models.Filament.diameter, models.Filament.density)
        .join(models.Spool, models.Spool.filament_id == models.Filament.id)
        .where(models.Spool.id == spool_id),
    )
    try:
        filament_info = result.one()
    except NoResultFound as exc:
        raise ItemNotFoundError("Filament not found for spool.") from exc

    # Calculate and use weight
    weight = weight_from_length(
        length=length,
        diameter=filament_info[0],
        density=filament_info[1],
    )
    await use_weight_safe(db, spool_id, weight)

    # Get spool with new weight and update first_used and last_used
    spool = await get_by_id(db, spool_id)

    if spool.first_used is None:
        spool.first_used = datetime.utcnow().replace(microsecond=0)
    spool.last_used = datetime.utcnow().replace(microsecond=0)

    await db.commit()
    await spool_changed(spool, EventType.UPDATED)
    return spool


async def measure(db: AsyncSession, spool_id: int, weight: float) -> models.Spool:
    """Record usage based on current gross weight of spool.

    Increases the used_weight attribute of the spool.
    Updates the first_used and last_used attributes where appropriate.

    Args:
        db (AsyncSession): Database session
        spool_id (int): Spool ID
        weight (float): Length of filament to consume, in mm

    Returns:
        models.Spool: Updated spool object

    """
    spool_result = await db.execute(
        sqlalchemy.select(models.Spool.initial_weight, models.Spool.used_weight, models.Spool.spool_weight).where(
            models.Spool.id == spool_id,
        ),
    )

    try:
        spool_info = spool_result.one()
    except NoResultFound as exc:
        raise SpoolMeasureError("Spool not found.") from exc

    initial_weight = spool_info[0]
    spool_weight = spool_info[2]
    if initial_weight is None or initial_weight == 0 or spool_weight is None or spool_weight == 0:
        # Get filament weight and spool_weight
        result = await db.execute(
            sqlalchemy.select(models.Filament.weight, models.Filament.spool_weight)
            .join(models.Spool, models.Spool.filament_id == models.Filament.id)
            .where(models.Spool.id == spool_id),
        )
        try:
            filament_info = result.one()
        except NoResultFound as exc:
            raise ItemNotFoundError("Filament not found for spool.") from exc

        if spool_weight is None or spool_weight == 0:
            spool_weight = filament_info[1]

        if initial_weight is None or initial_weight == 0:
            initial_weight = filament_info[0] if filament_info[0] is not None else 0

    if initial_weight is None or initial_weight == 0:
        raise SpoolMeasureError("Initial weight is not set.")

    initial_gross_weight = initial_weight + spool_weight

    # if the measurement is greater than the initial weight, set the initial weight to the measurement
    if weight > initial_gross_weight:
        return await reset_initial_weight(db, spool_id, weight - spool_weight)

    # Calculate the current net weight
    current_use = initial_gross_weight - spool_info[1]

    # Calculate the weight used since last measure
    weight_to_use = current_use - weight

    # If the measured weight is less than the empty weight, use the rest of the spool
    if (initial_gross_weight - weight_to_use) < spool_weight:
        weight_to_use = current_use - spool_weight

    return await use_weight(db, spool_id, weight_to_use)


async def find_locations(
    *,
    db: AsyncSession,
) -> list[str]:
    """Find a list of spool locations by searching for distinct values in the spool table."""
    stmt = sqlalchemy.select(models.Spool.location).distinct()
    rows = await db.execute(stmt)
    return [row[0] for row in rows.all() if row[0] is not None]


async def find_lot_numbers(
    *,
    db: AsyncSession,
) -> list[str]:
    """Find a list of spool lot numbers by searching for distinct values in the spool table."""
    stmt = sqlalchemy.select(models.Spool.lot_nr).distinct()
    rows = await db.execute(stmt)
    return [row[0] for row in rows.all() if row[0] is not None]


async def spool_changed(spool: models.Spool, typ: EventType) -> None:
    """Notify websocket clients that a spool has changed."""
    try:
        await websocket_manager.send(
            ("spool", str(spool.id)),
            SpoolEvent(
                type=typ,
                resource="spool",
                date=datetime.utcnow(),
                payload=Spool.from_db(spool),
            ),
        )
    except Exception:
        # Important to have a catch-all here since we don't want to stop the call if this fails.
        logger.exception("Failed to send websocket message")


async def reset_initial_weight(db: AsyncSession, spool_id: int, weight: float) -> models.Spool:
    """Reset inital weight to new weight and used_weight to 0."""
    spool = await get_by_id(db, spool_id)

    spool.initial_weight = weight
    spool.used_weight = 0
    await db.commit()
    await spool_changed(spool, EventType.UPDATED)
    return spool


async def rename_location(
    *,
    db: AsyncSession,
    current_name: str,
    new_name: str,
) -> None:
    """Rename all spools with the current location name to the new name."""
    await db.execute(
        sqlalchemy.update(models.Spool).where(models.Spool.location == current_name).values(location=new_name),
    )
    await db.commit()


async def rename_field_value(
    *,
    db: AsyncSession,
    field: str,
    value: str,
    new_value: str,
) -> int:
    """Replace one value of one spool field wherever it occurs, in a single statement.

    rename_location generalised from location to the spool's other string fields, including its
    custom ones. A client that has grouped spools by a field can rename a whole group this way
    without reading out its members and patching them one at a time -- which it could only do
    for the spools it had actually paged in, and not atomically.

    Only fields the SPOOL owns can be renamed. A filament's material or vendor is a property of
    another entity: rewriting it "for these spools" would change filaments other spools share.

    Archived spools are included -- the value is the value, and skipping them would silently
    leave half the spools behind.

    Like rename_location, no spool event is broadcast per row. The change is one statement over
    what may be hundreds of spools, and that fan-out is exactly what the websocket layer avoids
    elsewhere; other clients pick the change up on their next load.

    Returns the number of spools changed.
    """
    if field == "location":
        if len(new_value) > LOCATION_MAX_LENGTH:
            raise ValueError(f"A location can be at most {LOCATION_MAX_LENGTH} characters.")
        stmt = sqlalchemy.update(models.Spool).where(models.Spool.location == value).values(location=new_value)
    elif field.startswith(EXTRA_FIELD_PREFIX):
        field_key = _extra_field_key(await get_extra_fields(db, EntityType.spool), field)
        # Match on the DB-decoded scalar, so which JSON encoding wrote the value doesn't matter;
        # store the new one the way the rest of the API does.
        stmt = (
            sqlalchemy.update(models.SpoolField)
            .where(
                sqlalchemy.and_(
                    models.SpoolField.key == field_key,
                    extra_field_value_text(models.SpoolField.value) == value,
                ),
            )
            .values(value=json.dumps(new_value, ensure_ascii=False))
        )
    else:
        raise ValueError(
            f"Cannot rename values of '{field}'. Only fields the spool itself owns can be renamed: "
            f"location, or '{EXTRA_FIELD_PREFIX}<spool extra field key>'.",
        )

    result = await db.execute(stmt)
    await db.commit()
    return result.rowcount