from django.db import transaction

from .models import Plan, PlanVarietyChange


class _NoChange:
    pass


NO_CHANGE = _NoChange()


@transaction.atomic
def update_plan_with_variety_tracking(
    plan: Plan,
    *,
    crop=NO_CHANGE,
    variety=NO_CHANGE,
    notes=NO_CHANGE,
    reason: str = '',
):
    old_variety = plan.variety
    updated_fields = []

    if crop is not NO_CHANGE:
        plan.crop = crop
        updated_fields.append('crop')
    if variety is not NO_CHANGE:
        plan.variety = variety
        updated_fields.append('variety')
    if notes is not NO_CHANGE:
        plan.notes = notes
        updated_fields.append('notes')

    if updated_fields:
        plan.save(update_fields=updated_fields)

    if variety is not NO_CHANGE and _get_variety_id(old_variety) != _get_variety_id(plan.variety):
        handle_plan_variety_change(plan, old_variety=old_variety, new_variety=plan.variety, reason=reason)

    return plan


@transaction.atomic
def handle_plan_variety_change(plan: Plan, *, old_variety, new_variety, reason: str = ''):
    if _get_variety_id(old_variety) == _get_variety_id(new_variety):
        return None

    change = PlanVarietyChange.objects.create(
        field=plan.field,
        year=plan.year,
        plan=plan,
        old_variety=old_variety,
        new_variety=new_variety,
        reason=reason,
    )
    process_plan_variety_change(change)
    return change


def process_plan_variety_change(change: PlanVarietyChange):
    from apps.fertilizer.services import move_unspread_entries_for_variety_change

    moved_count = move_unspread_entries_for_variety_change(change)
    if moved_count != change.moved_entry_count:
        change.moved_entry_count = moved_count
        change.save(update_fields=['moved_entry_count'])
    return change


def _get_variety_id(variety):
    return getattr(variety, 'id', None)