Connect two models regardless of relationship type

AssociateModels.php

<?php

if (!function_exists('associate_models')) {
    /**
     * @param Model $model
     * @param Model $relatedModel
     * @param string $relationName
     */
    function associate_models(Model $model, Model $relatedModel, string $relationName)
    {
        /** @var Relations\Relation $relation */
        $relation = $model->$relationName();
        $expectedModel = $relation->getModel();

        if (!($relatedModel instanceof $expectedModel)) {
            $relation = get_class($model) . "::$relationName()";
            $expectedModel = get_class($expectedModel);
            $givenModel = get_class($relatedModel);

            throw new UnexpectedValueException("$relation expects the related model to be a $expectedModel."
                . " $givenModel given."
            );
        }

        if ($relation instanceof Relations\BelongsTo) {
            $relation->associate($relatedModel)->save();
        } elseif ($relation instanceof Relations\HasOneOrMany) {
            $relation->save($relatedModel);

            $relationships = $model->relationLoaded($relationName) ? $model->getRelation($relationName)
                : app(EloquentCollection::class);
            $relationships = ($relationships instanceof Model)
                ? app(EloquentCollection::class, ['items' => [$relationships]]) : $relationships;
            $relationships->push($relatedModel);

            $relation->match([$model], $relationships, $relationName);
        } elseif ($relation instanceof Relations\BelongsToMany) {
            $attributes = [];

            if ($relation instanceof Relations\MorphToMany) {
                foreach ($relation->getQuery()->getQuery()->wheres as $where) {
                    $conditionValidAssignment = $where['type'] == 'Basic' && $where['operator'] == '=';
                    $alreadyApplied = $where['column'] == $relation->getTable() . '.' . $relation->getMorphType();
                    $alreadyApplied |= $where['column'] == $relation->getMorphType();
                    $alreadyApplied |= $where['column'] == $relation->getQualifiedForeignPivotKeyName();
                    $alreadyApplied |= $where['column'] == $relation->getForeignPivotKeyName();

                    if ($conditionValidAssignment && !$alreadyApplied) {
                        $attributes[$where['column']] = $where['value'];
                    }
                }
            }

            $relation->attach($relatedModel, $attributes);
        } else {
            throw new UnexpectedValueException('Unsupported relation type ' . get_class($relation));
        }
    }
}