"""
Service layer for SiteSettings singleton.
Uses get-or-create pattern; only one row should ever exist.
"""
from dataclasses import dataclass
from typing import Optional
from sqlalchemy import inspect as sa_inspect, select
from sqlalchemy.orm import load_only
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.settings import SiteSettings
from app.schemas.settings import FeatureSettingsUpdate, SiteSettingsUpdate
from app.services.pricing import default_service_pricing, normalize_service_pricing


@dataclass(frozen=True)
class FeatureSettingsSnapshot:
    bookings_enabled: bool = True
    walks_enabled: bool = True
    messages_enabled: bool = True
    two_factor_enabled: bool = True
    audit_history_enabled: bool = True
    experiments_enabled: bool = True


class FeatureSettingsSchemaOutdatedError(RuntimeError):
    """Raised when feature settings are requested against an older schema."""


class ServicePricingSchemaOutdatedError(RuntimeError):
    """Raised when service pricing is requested against an older schema."""


async def _get_site_settings_column_names(db: AsyncSession) -> set[str]:
    connection = await db.connection()

    def _load_columns(sync_connection):
        inspector = sa_inspect(sync_connection)
        return {column["name"] for column in inspector.get_columns("site_settings")}

    return await connection.run_sync(_load_columns)


async def get_settings(db: AsyncSession, *, existing_columns: set[str] | None = None) -> Optional[SiteSettings]:
    column_names = existing_columns or await _get_site_settings_column_names(db)
    loadable_fields = [
        getattr(SiteSettings, column_name)
        for column_name in column_names
        if hasattr(SiteSettings, column_name)
    ]

    statement = select(SiteSettings).limit(1)
    if loadable_fields:
        statement = statement.options(load_only(*loadable_fields))

    result = await db.execute(statement)
    return result.scalars().first()


async def upsert_settings(db: AsyncSession, data: SiteSettingsUpdate) -> SiteSettings:
    settings_row = await get_settings(db)

    if settings_row is None:
        # Create with defaults + provided values
        init_data = {
            "site_name": "",
            "tagline": None,
            "logo_url": None,
            "footer_text": None,
            "social_links": {},
            "automatic_member_notifications_enabled": True,
            "nz_public_holiday_notifications_enabled": True,
            "invoice_reminder_notifications_enabled": True,
            "invoice_day_of_week": 1,
            "admin_notifications_cleared_before": None,
            "bookings_enabled": True,
            "walks_enabled": True,
            "messages_enabled": True,
            "two_factor_enabled": True,
            "audit_history_enabled": True,
            "experiments_enabled": True,
            "service_pricing": default_service_pricing(),
        }
        update_data = data.model_dump(exclude_unset=True)
        init_data.update(update_data)
        settings_row = SiteSettings(**init_data)
        db.add(settings_row)
    else:
        update_data = data.model_dump(exclude_unset=True)
        for field, value in update_data.items():
            setattr(settings_row, field, value)

    await db.flush()
    await db.refresh(settings_row)
    return settings_row


async def get_feature_settings_snapshot(db: AsyncSession) -> FeatureSettingsSnapshot:
    existing_columns = await _get_site_settings_column_names(db)
    row = await get_settings(db, existing_columns=existing_columns)
    if row is None:
        return FeatureSettingsSnapshot()

    return FeatureSettingsSnapshot(
        bookings_enabled=getattr(row, "bookings_enabled", True) if "bookings_enabled" in existing_columns else True,
        walks_enabled=getattr(row, "walks_enabled", True) if "walks_enabled" in existing_columns else True,
        messages_enabled=getattr(row, "messages_enabled", True) if "messages_enabled" in existing_columns else True,
        two_factor_enabled=getattr(row, "two_factor_enabled", True) if "two_factor_enabled" in existing_columns else True,
        audit_history_enabled=getattr(row, "audit_history_enabled", True) if "audit_history_enabled" in existing_columns else True,
        experiments_enabled=getattr(row, "experiments_enabled", True) if "experiments_enabled" in existing_columns else True,
    )


async def update_feature_settings_snapshot(
    db: AsyncSession,
    data: FeatureSettingsUpdate,
) -> FeatureSettingsSnapshot:
    existing_columns = await _get_site_settings_column_names(db)
    requested_fields = set(data.model_dump(exclude_unset=True).keys())
    missing_columns = sorted(field for field in requested_fields if field not in existing_columns)
    if missing_columns:
        raise FeatureSettingsSchemaOutdatedError(
            "Feature toggle columns are missing from site_settings. Run alembic upgrade head."
        )

    row = await get_settings(db, existing_columns=existing_columns)
    if row is None:
        row = SiteSettings(site_name="")
        db.add(row)
        await db.flush()

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

    await db.flush()
    await db.refresh(row)
    return await get_feature_settings_snapshot(db)


async def get_service_pricing_snapshot(db: AsyncSession) -> dict[str, dict[str, float | str]]:
    existing_columns = await _get_site_settings_column_names(db)
    row = await get_settings(db, existing_columns=existing_columns)
    if row is None:
        return default_service_pricing()

    if "service_pricing" not in existing_columns:
        return default_service_pricing()

    return normalize_service_pricing(getattr(row, "service_pricing", None))


async def update_service_pricing_snapshot(
    db: AsyncSession,
    *,
    service_pricing: dict,
) -> dict[str, dict[str, float | str]]:
    existing_columns = await _get_site_settings_column_names(db)
    if "service_pricing" not in existing_columns:
        raise ServicePricingSchemaOutdatedError(
            "Service pricing columns are missing from site_settings. Run alembic upgrade head."
        )

    row = await get_settings(db, existing_columns=existing_columns)
    if row is None:
        row = SiteSettings(site_name="", service_pricing=default_service_pricing())
        db.add(row)
        await db.flush()

    row.service_pricing = normalize_service_pricing(service_pricing)
    await db.flush()
    await db.refresh(row)
    return await get_service_pricing_snapshot(db)